FEBS Letters 582 (2008) 3757–3764

Hypothesis

TPPP orthologs are ciliary proteins

Ferenc Orosz*, Judit Ovadi

Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, H-1113 Budapest, Hungary

Received 1 August 2008; revised 1 October 2008; accepted 2 October 2008

Available online 16 October 2008

Edited by Michael R. Bubb

Abstract Tubulin polymerization promoting protein, (TPPP/p25), was identified as a brain-specific protein. The potentialfunction of this protein resembled that of MAPs. It is mainly ex-pressed in oligodendrocytes; however, immunopositivity was alsodetected in glial and neuronal inclusions in synucleinopathies.Here, we show that TPPP gene(s) are conserved in the genomesof ciliated organisms, but are lacking from the nonciliated ones.This recognition is based upon homologous gene sequence anal-ysis, in silico comparative genomic studies, bioinformatic searchand experimental evidence. Cilia (flagella) are microtubule-basedcellular extensions of sensory and/or motile function. TPPPorthologs are among the only 16 genes that can be found in allciliated organisms, suggesting that TPPP orthologs may beassociated with a basic function of cilia.� 2008 Federation of European Biochemical Societies.Published by Elsevier B.V. All rights reserved.

Keywords: TPPP/p25; TPPP ortholog; Cilia; Flagella;Microtubule; Synucleinopathy

1. Introduction

The research on eukaryotic cilium/flagellum has come to a

renaissance of interest, which was triggered by the recognition

that defects of this organelle are at the centre of several hu-

man disorders, including most importantly polycystic kidney

disease, the most common inherited disease in the US [1,2].

The cilium evolved very early in the development of eukary-

otes. This organelle, virtually in its present form, had been

present in the last common ancestor of eukaryotes [3,4].

However, it has been lost secondarily in multiple lineages as

red algae, cellular slime molds and in the majority of land

plants or fungi [5,6]. However, gametes and sperms of several

fungi and ancient plants such as mosses, ferns or Ginkgo pos-

sess flagella/cilia [6,7]. There are two main types of cilia, mo-

tile and non-motile or sensory. Their axonemes consist of

nine doublet microtubules; motile cilia (named also flagella)

contain an additional central pair of microtubules. The axo-

nemal microtubules of all cilia nucleate and extend from a ba-

sal body, a centriolar structure. Most cilia are assembled in a

Abbreviations: TPPP, tubulin polymerization promoting protein; IFT,intraflagellar transport; PSC, photoreceptor sensory cilium; CCV,clathrin-coated vesicle; SV, synaptic vesicle

*Corresponding author. Fax: +36 1 4665465.E-mail address: orosz@enzim.hu (F. Orosz).

0014-5793/$34.00 � 2008 Federation of European Biochemical Societies. Pu

doi:10.1016/j.febslet.2008.10.011

compartment separate from the cytoplasm via a process

called intraflagellar transport (IFT), mediated by the IFT

multiprotein complex (IFT particle) and IFT motors [8].

However, Plasmodium cilia and Drosophila sperm flagella

are assembled in the cytoplasm by a process that does not ap-

pear to require IFT [4,5]. The molecular makeup of motile

and non-motile cilia is likely to overlap substantially,

although each type will boast components required accommo-

dating their specific functions. For example, non-motile cilia

lack motility-associated proteins (e.g. outer and inner dynein

arm and radial spoke proteins, microtubule central pair-asso-

ciated proteins) but can be enriched for proteins related to

sensory perception [9].

Recently, we isolated a partially unfolded protein from bo-

vine brain [10] and named it tubulin polymerization promot-

ing protein/p25, (TPPP/p25), which has no well-defined

structure [11,12]. It was first identified by co-purification to-

gether with the tau protein kinase, Cdk5, in the bovine brain

[13], which probably causes its phosphorylation, together with

other kinases, ERK2 and PKA [14]. We have shown that it

promotes tubulin polymerization into normal and double

walled tubules and polymorph aggregates; its binding to pac-

litaxel-stabilized microtubules induces their bundling [14,15].

It exhibits microtubule associated proteins-like functions sta-

bilizing the microtubular network both in vitro and in trans-

fected HeLa and rat kidney cells [14,16]. The physiological

role of TPPP/p25 is unknown, although our data strongly

suggest that TPPP/p25 may take part in the stabilization of

the microtubular network. Under pathological conditions,

TPPP/p25 is enriched in filamentous a-synuclein bearing

Lewy bodies of Parkinson�s and diffuse Lewy body diseases,

as well as in glial inclusions of multiple system atrophy, as

demonstrated by immunohistochemistry and confocal micros-

copy [11,12,17,18]. TPPP/p25 promotes the fibrillization of a-

synuclein in vitro [19].

2. Phyletic distribution of TPPP proteins

TPPP/p25 is the first member of a new protein family, the

primary sequence of which differs from that of other known

proteins, but shows homology with TPPP-like hypothetical

proteins [15] sought via BLAST. There are two homologous

gene sequences in the human genome encoding two shorter

proteins, TPPP2/p18 and TPPP3/p20. Only the latter one

was isolated from bovine brain which displays similar micro-

tubule bundling activity as TPPP/p25 [20]. The paralogous

genes can be found only in vertebrates but not in other

blished by Elsevier B.V. All rights reserved.

Hs1

MA

DK

AK

PA

KA

AN

RT

PP

KS

PG

DP

SK

DR

AA

KR

LS

LE

SE

GA

GE

GA

AA

SP

EL

SA

LE

EA

Hs3

MA

AS

TD

MA

GL

EE

SC

iM

GD

KE

LE

AA

Nv

MS

DD

QL

QA

KM

bC

rM

SD

AL

KN

A

Hs1

FR

RF

AV

HG

DA

RA

TG

RE

MH

GK

NW

SK

LC

KD

CQ

VI

DG

RN

VT

VT

DV

DI

VF

SK

IK

GK

SC

Hs3

FR

KF

AI

HG

DP

KA

SG

QE

MN

GK

NW

AK

LC

KD

CK

VA

DG

KS

VT

GT

DV

DI

VF

SK

VK

GK

SA

Ci

YK

KF

MV

MG

NS

KA

TK

MT

GK

NF

AK

CL

KD

CK

VL

GP

KE

ST

NS

VD

II

FS

TL

KP

NS

EN

vF

ES

FC

AF

GA

GA

KG

AQ

PL

MD

NA

KF

GK

MF

RD

LH

LY

DQ

KF

TS

TD

TD

II

FS

RT

EV

KP

KT

EM

bE

LD

SA

KF

TK

LC

KE

TK

LI

SK

SL

TT

TD

AD

LI

FT

RV

KA

KG

QC

rF

IA

FA

SY

GK

GQ

MM

KQ

DM

DN

KN

FS

KC

IK

DS

GI

LD

KV

IT

ST

EV

DI

TF

MK

VK

AK

TD

Hs1

R

TI

TF

EQ

FQ

EA

LE

EL

AK

KR

FK

DK

SS

EE

AV

RE

VH

RL

IE

GK

AP

II

SG

VT

KA

IS

SP

TV

SR

Hs3

R

VI

NY

EE

FK

KA

LE

EL

AT

KR

FQ

GK

SK

EE

AF

DA

IC

QL

VA

GK

EP

AN

VG

VT

KA

KT

GG

AV

DR

Ci

KT

ID

FK

QF

KV

GL

EK

VA

AE

KK

IN

KE

DV

FN

KV

IN

GG

GP

VM

VG

VT

KT

SK

SG

GV

RK

Nv

RK

IN

FN

QF

KV

AL

GL

CA

EK

KF

GS

KD

QV

GK

LT

EK

IC

KG

KG

PA

TS

GA

TK

AV

KV

GG

VE

RM

bR

KI

GF

AE

FR

SA

LE

EV

AK

KT

GQ

DV

SA

VE

AK

VT

RA

GG

PQ

SS

GT

QA

DS

GG

VL

DR

Cr

RT

IN

FA

QF

CT

AL

EH

FA

AK

RG

VS

VD

SL

HA

KV

EA

AS

PT

SN

AT

QA

EA

VK

F

Hs1

L

TD

TT

KF

TG

SH

KE

RF

DP

SG

KG

KG

KA

GR

VD

LV

DE

SG

YV

SG

YK

HA

GT

YD

QK

VQ

GG

K21

9H

s3

LT

DT

SR

YT

GS

HK

ER

FD

ES

GK

GK

GI

AG

RQ

DI

LD

DS

GY

VS

AY

KN

AG

TY

DA

KV

KK

176

Ci

MT

DT

SQ

YT

GS

HK

ER

FG

AD

GK

GK

GL

DG

RV

DK

VD

AS

GY

VG

NY

KG

DG

TY

DQ

KV

SK

164

Nv

LT

DT

KC

YT

GS

HK

ER

FD

KS

GK

GK

GI

EG

RV

DR

DD

KA

AQ

GY

VG

NY

KG

EG

TY

DK

TH

172

Mb

MT

DT

SQ

YT

GS

HK

ER

FD

SE

GK

HK

GL

AG

ED

SR

AK

GT

GH

IP

A12

8C

rH

DD

KN

LY

TG

VY

KN

GG

PT

NI

DK

QA

AG

GL

AG

HL

DR

SP

AD

VR

GV

KF

151

Fig

.1.

Mu

ltip

lese

qu

ence

ali

gn

men

to

fse

ver

al

mem

ber

so

fth

eT

PP

Pfa

mil

yb

yC

lust

alW

[51

].T

he

ali

gn

men

tw

as

refi

ned

man

uall

y.

Hs1

,H

om

osa

pie

ns

TP

PP

/p2

5(N

P_

00

89

61

);H

s3,

Ho

mo

sap

ien

sT

PP

P3

/p2

0(N

P_

05

70

48

);C

i,C

ion

ain

test

ina

lis

(BW

358

08

3);

Nv

,N

ema

tost

ella

vect

ensi

s(X

P_

00

16

287

51

);M

b,

Monosi

ga

bre

vico

llis

(XP

_0

01

74

31

31

);C

r,C

hla

my

do

mo

na

sre

inh

ard

tii

FA

P2

65

(XP

_0

016

95

01

6).

Res

idu

esid

enti

cal

an

dsi

mil

ar

ina

tle

ast

all

bu

to

ne

spec

ies

are

ind

icate

db

yb

lack

an

dg

ray

ba

ckg

rou

nd

s,re

spec

tiv

ely.

Th

eso

-ca

lled

Pfa

m0

55

17

do

main

(2–

4li

nes

of

the

am

ino

aci

dse

qu

ence

s)in

vo

lves

the

majo

rp

art

of

the

pro

tein

sex

cep

tth

eN

-ter

min

al

tail

spec

ific

for

TP

PP

/p25s.

3758 F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764

organisms. BLASTP or TBLASTN analysis [21] was per-

formed on complete genome sequences and EST collections

available at the NCBI website using the sequences of human

TPPP proteins. Fig. 1 shows the sequence homology of sev-

eral TPPP proteins from unicellular organism to vertebrates.

Similarity can be seen in all parts of the proteins except the

N-terminal tail of TPPP/p25s, which is missing in other

homologs. A standard and simple method for determining

orthology is the reciprocal best hit approach. It helped to re-

veal 1:1 orthology also in cases when the BLAST E score was

higher than 1e�10. Our search has shown that such proteins/

genes can be found throughout the animal kingdom from

protists to vertebrates but not in prokaryotes, land plants

and fungi (Table 1). Thus they cannot be found in the com-

pleted genomes of Arabidopsis thaliana, Oryza sativa or Sac-

charomyces cerevisiae etc. No evidence for TPPP orthologs

was found either in bacteria or archaea. The species in Table

1 are only representative examples. (The only possible excep-

tion was the moss, Physcomitrella patens, which has a best-re-

ciprocal-hit protein, although the similarity is very low, and

probably it cannot be considered as a TPPP ortholog. The

very recent establishment of the draft genome sequence of

this model species and the comparison of its features with

those of flowering plants and the unicellular green algae re-

vealed genomic changes concomitant with the evolutionary

movement from aquatic environment to land, including loss

of some but not all flagellar components for gametic motility

as proteins of the outer dynein arms of flagella [22]. However,

we guess that it would be premature to make a final conclu-

sion concerning the occurrence of TPPP gene/protein in land

plants with ciliated sperm and we should wait until more gen-

omes will be available.) TPPP is also absent in the slime

mold, Dictyostelium discoideum. Interestingly, it occurs in

the biflagellated green alga, Chlamydomonas reinhardtii but

not in the red alga, Cyanidioschyzon merolae, which does

not have cilia/flagella. A detailed investigation of protists re-

vealed that a TPPP ortholog occurs in many species, however

it is absent from some of them. It can be found in Alveolates

including Apicomplexa (e.g. Plasmodium falciparum) and Cili-

ophora (e.g. Tetrahymena thermophila), in Euglenozoa (e.g.

Trypanosoma brucei) and in Diplomonadida (Giardia lamblia)

but not in Entamoeba histolytica (Entamoebidae) and Acan-

thamoeba castellanii (Acanthamoebidae).

The data listed in Table 1 show a tight parallel between the

phyletic distribution of cilia and the TPPP proteins, which sug-

gests that the TPPP gene is conserved in the genomes of cili-

ated organisms but is absent from those that are non-

ciliated. TPPP genes can be found in all organisms possessing

these organelles, independently of the type of the cilium: (i) in

organisms with motile cilia (most of the ciliated organisms); (ii)

in organisms with non-motile cilia only (e.g. C. elegans); (iii) in

organisms with compartmentalized (but not cytosol-assem-

bled) cilia (most of the ciliated organisms); (iv) and in organ-

isms with cytosol-assembled cilia (e.g. P. falciparum).

There are only two unicellular green algae, Ostreococcus

lucimarinus and Ostreococcus tauri, whose genomes contain

genes that can be considered as TPPP orthologs but these

species do not have cilia (cf. Table 1). Ostreococcus belonging

to the Prasinophyceae, an early-diverging class within the

green plant lineage, are the smallest known eukaryotes. They

have a very simple cellular organization, with no cell wall or

flagella, and with a single chloroplast and mitochondrion. In

Table 1Phyletic distribution of TPPP proteins.

Species Clade Group GenBank gi (Hypothetical) Protein *EST E-value Reciproc-al E-value Identitiy (%) Cilia/flagella

Mus musculus Opisthokonts Metazoa 33469051 NP_878259 2e�96 7e�101 91 YesMonodelphis domestica Opisthokonts Metazoa 126320804 XP_001363210 8e�97 4e�98 87 YesOrnithorhynchus anatinus Opisthokonts Metazoa 149443502 XP_001505656 3e�92 1e�99 82 YesGallus gallus Opisthokonts Metazoa 118086293 XP_001231864 2e�90 5e�99 80 YesXenopus tropicalis Opisthokonts Metazoa 156717851 NP_001096466 4e�76 1e�70 77 YesDanio rerio Opisthokonts Metazoa 41152061 NP_958492 3e�69 3e�64 70 YesCiona intestinalis Opisthokonts Metazoa 47769884 BW358083* (Ci0100135725) 2e�35 9e�35 47 YesBranchiostoma floridae Opisthokonts Metazoa 66297093 BW710519* 2e�55 3e�55 63 YesStrongylocentrotus purpuratus Opisthokonts Metazoa 115634898 XP_782492 1e�33 5e�29 48 YesDrosophila melanogaster Opisthokonts Metazoa 21357209 NP_648881 (CG4893) 5e�27 1e�17 38 YesCrassostrea virginica Opisthokonts Metazoa 31903501 AUF_101_G19_TJ* 2e�19 1e�18 32 YesCaenorhabditis elegans Opisthokonts Metazoa 17505795 NP_491219 (C32E8.3) 6e�28 1e�23 39 YesSchistosoma japonicum Opisthokonts Metazoa 29841410 AAP06442 4e�19 2e�17 36 YesNematostella vectensis Opisthokonts Metazoa 156371398 XP_001628751 4e�28 3e�32 48 YesSaccharomyces cerevisiae Opisthokonts Fungi No reciprocal best hit 3.5 – – NoMonosiga brevicollis Opisthokonts Choanoflagellida 163778230 XP_001743131 3e�23 3e�25 45 YesTetrahymena thermophila Alveolata Ciliophora 146181921 XP_001023601 2e�11 6e�2 23 YesCryptosporidium hominis Alveolata Apicomplexa 126649214 XP_001388280 3e�6 1e�3 16 YesPlasmodium falciparum Alveolata Apicomplexa 124806570 XP_001350760 2e�7 1e�6 20 YesTheileria parva Alveolata Apicomplexa 71028521 XP_763904 8e�8 2e�5 13 YesTrypanosoma brucei Euglenozoa Kinetoplastida 72387999 XP_844424 4e�11 1e�11 28 YesGiardia lamblia Diplomonadida Diplomonadida 159110571 XP_001705540 2e�8 4e�6 25 YesChlamydomonas reinhardtii Viridiplantae Chlorophyta 159473789 XP_001695016 (FAP265) 3e�15 2e�11 33 YesOstreococcus lucimarinus Viridiplantae Chlorophyta 145353793 XP_001421186 2e�6 0.028 17 NoOstreococcus tauri Viridiplantae Chlorophyta 116056988 CAL51415 (Unnamed protein) 6e�6 0.021 15 NoPhyscomitrella patens Viridiplantae Streptophyta 168035642 XP_001770318a 0.41 2.2 7 Yes (in sperm only)Arabidopsis thaliana Viridiplantae Streptophyta No reciprocal best hit 9.6 – – NoCyanidioschyzon merolae Rhodophyta Bangiophyceae No hit – – – NoDictyostelium discoideum Mycetozoa Dictyosteliida No reciprocal best hit 2.6 – – NoAcanthamoeba castellani Acanthamoebidae Acanthamoeba No hit – – – NoEntamoeba histolytica Entamoebidae Entamoeba No reciprocal best hit 1.8 – – NoEscherichia coli Proteobacteria Gammaproteobacteria No hit – – – Flagellin basedSalmonella typhimurium Proteobacteria Gammaproteobacteria No reciprocal best hit 1.1 – – Flagellin basedMethanococcus aeolicus Euryarchaeota Methanococci No reciprocal best hit 0.46 – – Flagellin based

The presence of orthologous TPPP proteins in different species was established using BLAST searches [21] and the reciprocal best hit approach. Protein and nucleotide sequences were searched usingBLASTP and TBLASTN, respectively, at http://www.ncbi.nlm.nih.gov/BLAST/, using the sequences of human TPPP proteins. Sequence identities were determined using CLUSTALW [51]. Asterisksstand for ESTs.aThis protein cannot be considered as a TPPP ortholog since no best-reciprocal-hit was found except between Homo sapiens and Physcomitrella patens. However, the Chlamydomonas reinhardtiiortholog has a different reciprocal best hit in Physcomitrella patens (XP_001761224) with higher similarity than the human (E-values are 0.14 and 0.37).

F.

Oro

sz,J

.O

vad

i/

FE

BS

Letters

58

2(

20

08

)3

75

7–

37

64

37

59

3760 F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764

the evolution of its small size, Ostreococcus have lost a num-

ber of genes involved in flagellum biosynthesis that are found

in Chlamydomonas, the flagellar unicellular green alga [23].

The TPPP orthologs we found in Ostreococcus are the most

divergent members of the family, with the far highest E-val-

ues. Even the Chlamydomonas reinhardtii ortholog, FAP265

protein, are more similar to the human TPPPs than to the

Ostreococcus homologs. FAP265 is identical in 31–33% with

the three human TPPPs but only in 21–23% with the Ostreo-

coccus orthologs. Taking into account that the phylogenetic

distance is much smaller between the two green alga families

than between mammals and algae, it can be hypothesized that

although the Ostreococcus ‘‘TPPPs’’ have not disappeared

from their genomes but they might lose their original func-

tions.

3. In silico studies suggest that TPPPs are ciliary proteins

The availability of numerous sequenced genomes from cili-

ated and non-ciliated eukaryotes has recently set the stage

for powerful comparative genomic studies. In silico subtrac-

tion of homologous genes found in non-ciliated organisms

from a ciliated genomic data set should enrich for genes that

have unique, cilium-specific functions. Li et al. [24] applied

such an approach by using a panel of genomes from different

organisms. The non-ciliated Arabidopsis genome was sub-

tracted from the genomic intersection between the ciliated hu-

man and Chlamydomonas genomes. The result was defined as

the so-called flagellar apparatus-basal body (FABB) proteome

containing 688 proteins, including TPPPs. The same ‘‘calcula-

tion’’ was carried out using other ciliated organism genomes

(M. musculus, C. intestinalis, C. elegans and D. melanogaster)

instead of the human genome, which resulted in data sets that

overlapped to a large degree with the FABB proteome. A

smaller amount of overlap was found in the case of C. elegans,

probably due to the lack of motile cilia in the nematode.

A similar study by Avidor-Reiss et al. [25] involved six cili-

ated organisms (D. melanogaster, H. sapiens, C. elegans, C.

reinhardtii, P. falciparum and T. brucei) and three non-ciliated

organisms (A. thaliana, S. cerevisiae and D. discoideum). Fol-

lowing genome subtractions, 187 ‘‘ciliary’’ genes were identi-

fied in total, which were divided into four classes, based on

the occurrence of the different type of cilia in the species.

Namely, genes conserved in organisms: (i) with motile cilia

(all ciliated organisms except C. elegans; 18 genes); (ii) with

compartmentalized cilia (all ciliated organisms except P. falci-

parum; 103 genes); (iii) with compartmentalized and motile ci-

lia (i.e. Homo sapiens, Chlamydomonas, Trypanosoma and

Drosophila but not C. elegans or Plasmodium; 50 genes); and

(iv) those are present in all ciliated organisms (16 genes).

These comparative genomic studies can identify cell body or

basal body proteins as well that support cilia function but are

not specifically localized to the organelle (e.g. cannot be de-

tected in proteomic analysis of isolated cilia). In other words,

they identify genes/proteins related specifically to cilia func-

tion. Importantly, TPPP homologs were found among the only

16 genes, which can be found in all ciliated organisms. This

finding suggests that they are connected to not a specific but

some kind of basic function of cilia.

Bioinformatic search supported further the possible ciliary

function of TPPPs. The study by Svoboda et al. [26] revealed

that the expression of C. elegans genes required for cilium bio-

genesis is controlled by the regulatory factor X (RFX)-type

transcription factor, DAF-19, which binds to a conserved pro-

moter element termed the ‘‘X-box’’. This indicated that C. ele-

gans X-box-containing genes, expressed exclusively in ciliated

cells, are likely to encode proteins with ciliary functions. Nota-

bly, human RFX3 and at least one of the two Drosophila RFX

transcription factors also regulate proper cilium assembly and

function. These findings prompted genome-wide searches for

such genes in C. elegans. Because the conserved C. elegans

X-boxes are typically �100-bp upstream of start codons [26],

X-boxes within 250-bp from start codon were searched using

different algorithms and X-box consensus sequences [27,28].

X-boxes positioned in this region were found in 164 [28] or

293 [27] of these gene promoters, including the X-box of TPPP

ortholog (C32e8.3, 87-bp from start codon) in the latter study

[27]. This finding was corroborated in [25] as well. These genes

can be considered as potential ciliogenic or ciliary genes,

although the two complementary data sets only overlap par-

tially.

4. Experimental support

Amputation of the flagella in Chlamydomonas strongly in-

duces expression of flagellar genes. A 3- to 12-fold upregula-

tion of the mRNAs for structural components of the flagella,

the IFT particle, and its molecular motors was observed

30 min after deflagellation, whereas genes encoding non-flagel-

lar proteins were not induced [29]. Proteins that function in

both the flagellum and the cell body usually were only weakly

induced. Therefore, several groups used the deflagellation of C.

reinhardtii to identify further flagellar genes. DNA oligonu-

cleotide microarray [30] or real-time PCR [30,31] were used

to measure changes in transcript level during flagellar regener-

ation. Indeed, a substantial fraction of the genes was upregu-

lated. The TPPP ortholog was also induced, more than two-

fold [31]. It should be noted that in addition to revealing genes

that encode flagellar/ciliary components, this approach also

identifies genes whose products are involved in regulating fla-

gellar assembly or function but are themselves not components

of cilia or flagella. However, proteomic analysis after isolation

of flagella/cilia and basal body can differentiate among these

possibilities.

The very few proteomic studies have been carried out mostly

on unicellular organisms, and, except a pioneering one in 2002

[32], have been published in the last two years. In these works

the cilia were isolated, and peptides were generated by proteo-

lytic digestion either directly or following 1D and/or 2D gel

electrophoresis separations of the proteins, which was followed

by liquid chromatography (LC)–mass spectrometric (MS)

analyses of the peptides. Generally, proteins represented by

at least two (but preferentially more) peptides are considered

as potential ciliary ones.

The most detailed investigations involved the quasi model

organism of ciliary/flagellar species, the biflagellated green

alga, Chlamydomonas reinhardtii. Not only the flagellum but

also its sub-organellar parts (axoneme, membrane, matrix)

[31] and the basal bodies [33] were isolated and studied sepa-

rately. Six hundred fifty-two proteins were represented by at

least two peptides in the flagella preparation and 45 proteins

F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764 3761

were validated as basal body candidate proteins. The TPPP

ortholog (XP_001695016 or FAP265) was found exclusively

in the flagella, in the matrix preparation. The matrix contains

components that are not tightly associated with either the axo-

neme or the membrane such as IFT proteins. However, it is

questionable whether FAP265 protein itself is an IFT protein.

It was not found in the isolated IFT particle of C. reinhardtii

[8] and the TPPP orthologous gene can be found in each Plas-

modium species, the cilia of which are assembled in the cyto-

plasm by a process that does not require IFT.

Recently, the ciliary proteome of the uniflagellated parasite,

Tripanosoma brucei [34], and the ciliated Tetrahymena thermo-

phila [35] was also established. Although both protists are

known to possess a TPPP orthologous gene (thus probably

the protein as well), the TPPP protein has not been found in

these studies. In the latter case [35] the reason may have been

the loss of extremely basic proteins, such as TPPP during 2D

electrophoresis. In general, biochemical fractionation might re-

move ciliary components therefore proteins of low abundance

might not be identified by at least two peptides. For example,

although all the so-called Bardet–Biedl syndrome (a ciliary dis-

order) proteins studied in C. elegans have been shown to be

components of the IFT machinery, none of the homologous

proteins from humans, Chlamydomonas or Tetrahymena were

identified in the proteomic studies [9].

The first attempt to identify a mammalian ciliary axoneme

proteome, using cilia released from human bronchial epithelial

tissue culture cells as starting material, was described by

Ostrowski et al. [32]. A total of 214 proteins were identifiable

on the basis of one or more peptide match(es). Sixty-five of

them were identified as known or likely ciliary components,

including TPPP3/p20. (TPPP3/p20 was identified on the basis

of a single peptide only. The results of more recent proteomic

studies usually involve only proteins identified on more

matches. In addition, the peptides, which the identifications

were based on, were not given, in contrast to recent studies.

Thus data provided in this early paper showing that TPPP3/

p20 is a ciliary protein would not be satisfactory according

to the present-day standards of proteomic works).

All the studies mentioned above analyzed motile cilia/fla-

gella. The first proteomic study of non-motile (sensory) cilia

is a very recent one by Liu et al. [36]. Specialized versions of

non-motile cilia are involved in many aspects of sensation.

The single photoreceptor sensory cilium (PSC) or outer seg-

ment elaborated by each rod and cone photoreceptor cell of

the retina is a classic example.

The PSC complex comprises the outer segment and its cyto-

skeleton, including the axoneme, basal body and ciliary rootlet

extending into the inner segment of photoreceptor cells. A de-

tailed analysis of the mouse PSC complex proteome revealed

mammalian cilia to be several times more complex than the ci-

lia of unicellular organisms. The PSC complex contains 1968

proteins represented by three or more unique peptides, includ-

ing �1500 proteins not detected in cilia from lower organisms.

1185 of them are derived from the outer segment (i.e. cilium

and basal body), including TPPP/p25, represented by six pep-

tides.

This year proteomic analysis of a membrane preparation from

rat olfactory sensory cilia was also published; however, this

study has not intended to identify the entire set of ciliary proteins

but only that of the ciliary membrane [37]. Two hundred sixty-

eight proteins, the half of which was membrane proteins, were

identified, with significant amount of contaminating material.

TPPP/p25 was not found in this preparation. It is in accordance

with the data of [31] where the TPPP ortholog was found in the

matrix but not in the membrane fraction.

The mammalian proteomic reports identified TPPP/p25 in

the modified sensory cilia of photoreceptor cells [36] and

TPPP3/p20 in the motile cilia of bronchial epithelial tissue cells

[32]. Further studies will enlighten whether the two paralogs

really share in the roles: are TPPP/p25 and TPPP3/p20 present

in non-motile and motile cilia, respectively?

5. Potential role of TPPPs in ciliary function

The combination of the results of the different complemen-

tary studies suggests that TPPP orthologs are ciliary proteins

and they are integral part of cilia/flagella. The TPPP orthologs

were found among the only 16 genes, which can be found in all

ciliated organisms. This finding suggests that they are con-

nected to a basic function of cilia. The most general feature of

eukaryotic cilium is that its axoneme consisting of nine dou-

blets of microtubules serves as its ‘‘skeleton’’. Beside microtu-

bules, the axoneme contains many other proteins and protein

complexes necessary for its function. TPPP proteins can stabi-

lize microtubules via their high bundling activity. Experiments

with isolated TPPP proteins and with human cell lines have

shown that TPPP/p25 and TPPP3/p20, in addition to their

tubulin polymerization promoting activities, cross-link micro-

tubules making them resistant against the effects of anti-micro-

tubular agents such as vinblastine [16,20]. Such stabilizing effect

of TPPP proteins might manifest itself at the ultrastructural

organization of both the axonemal and the axonal microtu-

bules.

Another, almost universally cilia-associated characteristic is

that their assembly relies on IFT except Plasmodium cilia and

Drosophila sperm flagella, which are assembled in the cyto-

plasm by a process that does not appear to require IFT. IFT

is characterized by a bidirectional movement of protein parti-

cles in cilia between the microtubular axoneme and the outer

membrane [38]. The movement of IFT particles is microtubule

dependent and driven by motor proteins kinesin and dynein.

The IFT particle can be isolated as a multiprotein complex

[8]. Electron microscopic studies indicate that the IFT complex

is linked to the ciliary membrane but the mechanism of associ-

ation is unknown. As suggested by Jekely and Arendt [4], the

IFT probably evolved as a special form of clathrin-coated ves-

icle (CCV) transport. CCVs are postulated to be responsible

for the recycling of synaptic vesicles (SVs) during neurotrans-

mission (For review see Ref. [39]). After exocytosis, SVs are re-

trieved by clathrin-dependent endocytosis to restore the

primed vesicle pool and are locally recycled to regenerate exo-

cytosis-competent vesicles. CCVs retrieve SV membranes from

the plasma membrane after SVs collapse, concomitant with

neurotransmitter release. Very recently, it has been suggested

[39] on the basis of proteomic analysis of SVs and CCVs that

TPPP/p25, as a protein transiently associated with the SV/CCV

membrane during the SV life cycle, may have a role in the

organelle transport and interaction of the vesicles with the

nerve terminal cytoskeleton. TPPPs are not integral part of

either SVs/CCVs or IFT particle but TPPP/p25 was identified

as a vesicle membrane-associated protein that attaches and

3762 F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764

detaches during the vesicle cycle in a time-dependent manner.

One can hypothesize a similar role for TPPPs in IFT as well.

As it was suggested in [4] the eukaryotic cilium/flagellum

probably is an autogenous innovation of eukaryotes. This is

likely true for the IFT machinery as well, and the hypothesis

is also supported by the evolutionary history of ciliary axo-

neme proteins, including first of all tubulin. The fact that an-

other ciliary protein, TPPP, has no homologs in prokaryotes

possessing flagellin based flagellum fits to this view. However,

it does not exclude the other explanations, as the endosymbi-

otic [40] or the viral invasion [41] hypothesis.

Until very recently [42] TPPP/p25 has been considered as a

brain-specific protein since it was identified in oligodendro-

cytes and in the neuropil [11,43], and was studied in brain tis-

sues by immunohistochemistry up to now. A study of the

spatial and temporal distribution of TPPP/p25 in the develop-

ing rat brain showed that the protein appeared only in differ-

entiating oligodendrocytes and co-localized with bIV-tubulin

when the cells reached the myelinating state [44]. (This tubulin

isoform appears in myelinating oligodendrocytes but not in

oligodendrocyte progenitor cells). Our recent data [45] ob-

tained with oligodendrocyte progenitor cells from rat brain

also revealed that TPPP/p25 is virtually not present in progen-

itor cells but strongly up-regulated in differentiating oligoden-

drocytes and was co-immunostained with bIV-tubulin. Very

recently, genome-wide transcriptional profiling comparing oli-

godendrocytes from developing and mature mouse forebrain

have revealed gene expression changes during oligodendrocyte

specification and differentiation [46]. Not only TPPP but also

TPPP3 gene was found among the genes whose expression was

significantly (more than 10-times) enriched in myelinating oli-

godendrocytes compared to oligodendrocyte progenitor cells.

Myelin basic protein, a marker protein of the differentiated

oligodendrocytes, was shown to interact with TPPP/p25 [18].

The formation of an adequate microtubule network by devel-

oping oligodendrocytes is essential for normal myelination of

axons. TPPP/p25, having high affinity for microtubules, may

denote an important part of the microtubule-based transport-

ing network needed for myelin formation in the developing

brain and renewal in the adult brain.

The expression of TPPP/p25 during differentiation resembles

to the phenomenon that cilia are only assembled when cells

exit the cell-cycle from mitosis into a stationary or quiescent

and/or differentiated state, and vice versa, entry into the cell cy-

cle is preceded by ciliary resorption [47]. Several ciliary assem-

bly proteins are known to influence cell-cycle progression

[48,49]. We showed that TPPP/p25 inhibited cell division [16]

and its accumulation increased the number of cells in the phase

of cytokinesis [45]. One can hypothesize that TPPP was an an-

cient ciliary-regulatory protein that diverged to function more

generally in differentiation. The analogy is further supported

by our recent data which showed that TPPP/p25 is expressed

in non-neoplastic differentiated oligodendrocytes but not in

rapidly proliferating oligodendroglioma cells [50]. On the other

hand, one can not exclude the possibility that, during the pro-

cess of neoplastic transformation, oligodendrocytes lose their

ability to express TPPP/p25, or this feature is suppressed by

other, yet unidentified, genetic or epigenetic factors. This idea

is compatible with the ‘‘anti-mitotic activity’’ of TPPP/p25

shown in Drosophila embryos [15].

The data presented here support that the TPPP orthologs oc-

cur both in cilia and in the cell body. The relative low upregu-

lation (roughly two-fold) of the TPPP ortholog gene in

deflagellated C. reinhardtii [31] also suggests this dual localiza-

tion. Their functions can be similar in both cellular environ-

ments: stabilization of microtubules and/or participation in

cytoskeleton based transport processes. These functions can

be only analogous and manifest themselves depending on the

cell type. However, we are intrigued by the possibility of a more

intimate relationship between TPPP/p25, cilia and cell cycle

progression: the genesis and disassembly of the cilia is con-

trolled by cell cycle, and vice versa, which is affected by

TPPP/p25 via modulation of the reorganization of microtubule

ultrastructures.

Acknowledgements: The authors are grateful to Laszlo Patthy for hiscomments on the manuscript. This work was supported by FP6–2003-LIFESCIHEALTH-I: BioSim to J.O.; and by the HungarianNational Scientific Research Fund Grants Nos. OTKA T-046071and T-67963 to J.O. and T-049247 to F.O., respectively.

References

[1] Pan, J., Wang, Q. and Snell, W. (2005) Cilium-generated signalingand cilia-related disorders. Lab. Invest. 85, 452–463.

[2] Fliegauf, M., Benzing, T. and Omran, H. (2007) When cilia gobad: cilia defects and ciliopathies. Nat. Rev. Mol. Cell. Biol. 8,880–893.

[3] Cavalier-Smith, T. (2002) The phagotrophic origin of eukaryotesand phylogenetic classification of Protozoa. Int. J. Syst. Evol.Microbiol. 52, 297–354.

[4] Jekely, G. and Arendt, D. (2006) Evolution of intraflagellartransport from coated vesicles and autogenous origin of theeukaryotic cilium. BioEssays 28, 191–198.

[5] Pazour, G.J. (2004) Comparative genomics: prediction of theciliary and basal body proteome. Curr. Biol. 14, R575–R577.

[6] Silflow, C.D. and Lefebvre, P.A. (2001) Assembly and motility ofeukaryotic cilia and flagella. Lessons from Chlamydomonasreinhardtii. Plant Physiol. 127, 1500–1507.

[7] Dick, M.W. (1997) Fungi flagella and phylogeny. Mycol. Res.101, 385–394.

[8] Cole, D.G. (2003) The intraflagellar transport machinery ofChlamydomonas reinhardtii. Traffic 4, 435–442.

[9] Inglis, P.N., Boroevich, K.A. and Leroux, M.R. (2006) Piecingtogether a ciliome. Trend Genet. 22, 491–500.

[10] Hlavanda, E., Kovacs, J., Olah, J., Orosz, F., Medzihradszky,K.F. and Ovadi, J. (2002) Brain-specific p25 protein binds totubulin and microtubule and induces aberrant microtuble assem-blies at substoichiometreic concentration. Biochemistry 41, 8657–8664.

[11] Kovacs, G.G., Laszlo, L., Kovacs, J., Jensen, P.H., Lindersson,E., Botond, G., Molnar, T., Perczel, A., Hudecz, F., Mezo, G.,Erdei, A., Tirian, L., Lehotzky, A., Gelpi, E., Budka, H. andOvadi, J. (2004) Natively unfolded tubulin polymerization pro-moting protein TPPP/p25 is a common marker of alpha-synuc-leinopathies. Neurobiol. Dis. 17, 155–162.

[12] Orosz, F., Kovacs, G.G., Lehotzky, A., Olah, J., Vincze, O. andOvadi, J. (2004) TPPP/p25: from unfolded protein to misfoldingdisease. Prediction and experiments. Biol. Cell 96, 701–711.

[13] Takahashi, M., Tomizawa, K., Ishiguro, K., Sato, K., Omori, A.,Sato, S., Shiratsuchi, A., Uchida, T. and Imahori, K. (1991) Anovel brain-specific 25 kDa protein (p25) is phosphorylated by aSer/Thr-Pro kinase (TPK II) from tau protein kinase fractions.FEBS Lett. 289, 37–43.

[14] Hlavanda, E., Klement, E., Kokai, E., Kovacs, J., Vincze, O.,Tokesi, N., Orosz, F., Medzihradszky, K.F., Dombradi, V. andOvadi, J. (2007) Phosphorylation blocks the activity of tubulinpolymerization promoting protein (TPPP): identification of sitestargeted by different kinases. J. Biol. Chem. 282, 29531–29539.

[15] Tirian, L., Hlavanda, E., Olah, J., Horvath, I., Orosz, F., Szabo,B., Kovacs, J., Szabad, J. and Ovadi, J. (2003) TPPP/p25promotes tubulin assemblies and blocks mitotic spindle forma-tion. Proc. Natl. Acad. Sci. USA 100, 13976–13981.

F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764 3763

[16] Lehotzky, A., Tirian, L., T}okesi, N., Lenart, P., Szabo, B.,Kovacs, J. and Ovadi, J. (2004) Dynamic targeting of microtu-bules by TPPP/p25 affects cell survival. J. Cell Sci. 117, 6249–6259.

[17] Kovacs, G.G., Gelpi, E., Lehotzky, A., Hoftberger, R., Erdei, A.,Budka, H. and Ovadi, J. (2007) The brain-specific protein TPPP/p25 in pathological protein deposits of neurodegenerative dis-eases. Acta Neuropathol. 113, 153–161.

[18] Song, Y.J.C., Lundvig, D.M.S., Huang, Y., Gai, W.P., Blum-bergs, P.C., Højrup, P., Otzen, D., Halliday, G.M. and Jensen,P.H. (2007) P25 alpha relocalizes in oligodendroglia from myelinto cytoplasmic inclusions in multiple system atrophy. Am. J.Pathol. 171, 1291–1303.

[19] Lindersson, E., Lundvig, D., Petersen, C., Madsen, P., Nyeng-aard, J.R., Højrup, P., Moos, T., Otzen, D., Gai, W.P.,Blumbergs, P.C. and Jensen, P.H. (2005) P25alpha Stimulatesalpha-synuclein aggregation and is co-localized with aggregatedalpha-synuclein in alpha-synucleinopathies. J. Biol. Chem. 280,5703–5715.

[20] Vincze, O., T}okesi, N., Olah, J., Hlavanda, E., Zotter, A.,Horvath, I., Lehotzky, A., Tirian, L., Medzihradszky, K.F.,Kovacs, J., Orosz, F. and Ovadi, J. (2006) TPPP proteins:members of a new family with distinct structures and functions.Biochemistry 45, 13818–13826.

[21] Altschul, S.F., Madden, T.L., Schaffer, A.A., Zhang, J., Zhang,Z., Miller, W. and Lipman, D.J. (1997) Gapped BLAST and PSI-BLAST: a new generation of protein database search programs.Nucl. Acid Res. 25, 3389–3402.

[22] Rensing, S.A., Lang, D., Zimmer, A.D., Terry, A., Salamov, A.,Shapiro, H., Nishiyama, T., Perroud, P.F., Lindquist, E.A.,Kamisugi, Y., Tanahashi, T., Sakakibara, K., Fujita, T., Oishi,K., Shin-I, T., Kuroki, Y., Toyoda, A., Suzuki, Y., Hashimoto,S., Yamaguchi, K., Sugano, S., Kohara, Y., Fujiyama, A.,Anterola, A., Aoki, S., Ashton, N., Barbazuk, W.B., Barker, E.,Bennetzen, J.L., Blankenship, R., Cho, S.H., Dutcher, S.K.,Estelle, M., Fawcett, J.A., Gundlach, H., Hanada, K., Heyl, A.,Hicks, K.A., Hughes, J., Lohr, M., Mayer, K., Melkozernov, A.,Murata, T., Nelson, D.R., Pils, B., Prigge, M., Reiss, B., Renner,T., Rombauts, S., Rushton, P.J., Sanderfoot, A., Schween, G.,Shiu, S.H., Stueber, K., Theodoulou, F.L., Tu, H., Van de Peer,Y., Verrier, P.J., Waters, E., Wood, A., Yang, L., Cove, D.,Cuming, A.C., Hasebe, M., Lucas, S., Mishler, B.D., Reski, R.,Grigoriev, I.V., Quatrano, R.S. and Boore, J.L. (2008) ThePhyscomitrella genome reveals evolutionary insights into theconquest of land by plants. Science 319, 64–69.

[23] Palenik, B., Grimwood, J., Aerts, A., Rouze, P., Salamov, A.,Putnam, N., Dupont, C., Jorgensen, R., Derelle, E., Rombauts,S., Zhou, K., Otillar, R., Merchant, S.S., Podell, S., Gaasterland,T., Napoli, C., Gendler, K., Manuell, A., Tai, V., Vallon, O.,Piganeau, G., Jancek, S., Heijde, M., Jabbari, K., Bowler, C.,Lohr, M., Robbens, S., Werner, G., Dubchak, I., Pazour, G.J.,Ren, Q., Paulsen, I., Delwiche, C., Schmutz, J., Rokhsar, D., Vande Peer, Y., Moreau, H. and Grigoriev, I.V. (2007) The tinyeukaryote Ostreococcus provides genomic insights into theparadox of plankton speciation. Proc. Natl. Acad. Sci. USA104, 7705–7710.

[24] Li, J.B., Gerdes, J.M., Haycraft, C.J., Fan, Y., Teslovich, T.M.,May-Simera, H., Li, H., Blacque, O.E., Li, L., Leitch, C.C.,Lewis, R.A., Green, J.S., Parfrey, P.S., Leroux, M.R., Davidson,W.S., Beales, P.L., Guay-Woodford, L.M., Yoder, B.K., Stormo,G.D., Katsanis, N. and Dutcher, S.K. (2004) Comparativegenomics identifies a flagellar and basal body proteome thatincludes the BBS5 human disease gene. Cell 117, 541–552.

[25] Avidor-Reiss, T., Maer, A.M., Koundakjian, E., Polyanovsky,A., Keil, T., Subramaniam, S. and Zuker, C.S. (2004) Decodingcilia function: defining specialized genes required for compart-mentalized cilia biogenesis. Cell 117, 527–539.

[26] Svoboda, P., Adler, H.T. and Thomas, J.H. (2000) The RFX-typetranscription factor DAF-19 regulates sensory neuron ciliumformation in C. elegans. Mol. Cell 5, 411–421.

[27] Blacque, O.E., Perens, E.A., Boroevich, K.A., Inglis, P.N., Li, C.,Warner, A., Khattra, J., Holt, R.A., Ou, G., Mah, A.K., McKay,S.J., Huang, P., Swoboda, P., Jones, S.J., Marra, M.A., Baillie,D.L., Moerman, D.G., Shaham, S. and Leroux, M.R. (2005)

Functional genomics of the cilium, a sensory organelle. Curr.Biol. 15, 935–941.

[28] Efimenko, E., Bubb, K., Mak, H.Y., Holzman, T., Leroux, M.R.,Ruvkun, G., Thomas, J.H. and Swoboda, P. (2005) Analysis ofxbx genes in C. elegans. Development 132, 1923–1934.

[29] Lefebvre, P.A. and Rosenbaum, J.L. (1986) Regulation of thesynthesis and assembly of ciliary and flagellar proteins duringregeneration. Annu. Rev. Cell Biol. 2, 517–546.

[30] Stolc, V., Samanta, M.P., Togprasit, W. and Marshall, F.W.(2005) Genome-wide transcriptional analysis of flagellar regener-ation in Chlamydomonas reinhardtii identifies orthologs of ciliary-disease genes. Proc. Natl. Acad. Sci. USA 102, 3703–3707.

[31] Pazour, G.J., Agrin, N., Leszyk, J. and Witman, G.B. (2005)Proteomic analysis of a eukaryotic cilium. J. Cell Biol. 170, 103–113.

[32] Ostrowski, L.E., Blackburn, K., Radde, K.M., Moyer, M.B.,Schlatzer, D.M., Moseley, A. and Boucher, R.C. (2002) Aproteomic analysis of human cilia: identification of novelcomponents. Mol. Cell. Proteom. 1, 451–465.

[33] Keller, L.C., Romijn, E.P., Zamora, I., Yates 3rd, J.R. andMarshall, W.F. (2005) Proteomic analysis of isolated chlamydo-monas centrioles reveals orthologs of ciliary-disease genes. Curr.Biol. 15, 1090–1098.

[34] Broadhead, R., Dawe, H.R., Farr, H., Griffiths, S., Hart, S.R.,Portman, N., Shaw, M.K., Ginger, M.L., Gaskell, S.J., McKean,P.G. and Gull, K. (2006) Flagellar motility is required for theviability of the bloodstream trypanosome. Nature 440, 224–227.

[35] Smith, J.C., Northey, J.G., Garg, J., Pearlman, R.E. and Siu,K.W. (2005) Robust method for proteome analysis by MS/MSusing an entire translated genome: demonstration on the ciliomeof Tetrahymena thermophila. J. Proteome Res. 4, 909–919.

[36] Liu, Q., Tan, G., Levenkova, N., Li, T., Pugh Jr, E.N., Rux, J.J.,Speicher, D.W. and Pierce, E.A. (2007) The proteome of themouse photoreceptor sensory cilium complex. Mol. Cell Proteom.6, 1299–1317.

[37] Mayer, U., Ungerer, N., Klimmeck, D., Warnken, U., Schnolzer,M., Frings, S. and Mohrlen, F. (2008) Proteomic analysis of amembrane preparation from rat olfactory sensory cilia. Chem.Senses 33, 145–162.

[38] Scholey, J.M. (2003) Intraflagellar transport. Annu. Rev. CellDev. Biol. 19, 423–443.

[39] Burre, J. and Volknandt, W. (2007) The synaptic vesicle prote-ome. J. Neurochem. 101, 1448–1462.

[40] Margulis, L., Chapman, M., Guerrero, R. and Hall, J. (2006) Thelast eukaryotic common ancestor (LECA): acquisition of cyto-skeletal motility from aerotolerant spirochetes in the ProterozoicEon. Proc. Natl. Acad. Sci. USA 103, 13080–13085.

[41] Satir, P., Guerra, C. and Bell, A.J. (2007) Evolution andpersistence of the cilium. Cell Motil. Cytoskel. 64, 906–913.

[42] Acevedo, K., Li, R., Soo, P., Suryadinata, R., Sarcevic, B.,Valova, V.A., Graham, M.E., Robinson, P.J. and Bernard, O.(2007) The phosphorylation of p25/TPPP by LIM kinase 1inhibits its ability to assemble microtubules. Exp. Cell Res. 313,4091–4106.

[43] Takahashi, M., Tomizawa, K., Fujita, S.C., Sato, K., Uchida, T.and Imahori, K. (1993) A brain-specific protein p25 is localizedand associated with oligodendrocytes, neuropil, and fiber-likestructures of the CA3 hippocampal region in the rat brain. J.Neurochem. 60, 228–235.

[44] Skjoerringe, T., Lundvig, D.M., Jensen, P.H. and Moos, T. (2006)P25a/tubulin polymerization promoting protein expression bymyelinating oligodendrocytes of the developing rat brain. J.Neurochem. 99, 333–342.

[45] Lehotzky, A., T}okesi, N., Gonzalez-Alvarez, I., Merino, V.,Bermejo, M., Orosz, F., Lau, P., Kovacs, G.G. and Ovadi, J.(2008) Progress in the development of early diagnosis and a drugwith unique pharmacology to improve cancer therapy. Phil.Trans. A: Math. Phys. Eng. Sci. 366, 3599–3617.

[46] Cahoy, J.D., Emery, B., Kaushal, A., Foo, L.C., Zamanian, J.L.,Christopherson, K.S., Xing, Y., Lubischer, J.L., Krieg, P.A.,Krupenko, S.A., Thompson, W.J. and Barres, B.A. (2008) Atranscriptome database for astrocytes, neurons, and oligodendro-cytes: a new resource for understanding brain development andfunction. J. Neurosci. 28, 264–278.

3764 F. Orosz, J. Ovadi / FEBS Letters 582 (2008) 3757–3764

[47] Quarmby, L.M. and Parker, D.K. (2005) Cilia and the cell cycle?J. Cell Biol. 169, 707–710.

[48] Pugacheva, E.N., Jablonski, S.A., Hartman, T.R., Henske, E.P.and Golemis, E.A. (2007) HEF1-dependent Aurora A activationinduces disassembly of the primary cilium. Cell 129, 1351–1363.

[49] Pan, J. and Snell, W. (2007) The primary cilium: keeper of the keyto cell division. Cell 129, 1255–1257.

[50] Preusser, M., Lehotzky, A., Budka, H., Ovadi, J. and Kovacs,G.G. (2007) TPPP/p25 in brain tumours: expression in non-neoplastic oligodendrocytes but not in oligodendroglioma cells.Acta Neuropathol. 113, 213–215.

[51] Pearson, W.R. (1990) Rapid and sensitive sequence comparisonwith FASTP and FASTA. Meth. Enzymol. 183, 63–98.