Hox genes play a fundamental role in the establishment of chordate body plan, especially in the anteroposterior patterning of the nervous system. Particularly interesting are the anterior groups of Hox genes (Hox1-Hox4) since their expression is coupled to the control of regional identity in the anterior regions of the nervous system, where the highest structural diversity is observed. Ascidians, among chordates, are considered a good model to investigate evolution of Hox gene, organisation, regulation and function. We report here the cloning and the expression pattern of CiHox3, a Ciona intestinalis anterior Hox gene homologous to the paralogy group 3 genes. In situ hybridization at the larva stage revealed that CiHox3 expression was restricted to the visceral ganglion of the central nervous system. The presence of a sharp posterior boundary and the absence of transcript in mesodermal tissues are distinctive features of CiHox3 expression when compared to the paralogy group 3 in other chordates. We have investigated the regulatory elements underlying CiHox3 neural-specific expression and, using transgenic analysis, we were able to isolate an 80 bp enhancer responsible of CiHox3 activation in the central nervous system (CNS). A comparative study between mouse and Ciona Hox3 promoters demonstrated that divergent mechanisms are involved in the regulation of these genes in vertebrates and ascidians.

Reference

Amores
A.
,
Force
A.
,
Yan
Y. L.
,
Joly
L.
,
Amemiya
C.
,
Fritz
A.
,
Ho
R.
,
Langeland
J.
,
Prince
V.
,
Wang
Y. L.
,
Westerfield
M.
,
Ekker
M.
,
Postlehwait
J.
(
1998
)
Zebrafish hox cluster and vertebrate genome evolution.
Science
282
,
1711
1714
Aparicio
S.
,
Hawker
K.
,
Cottage
A.
,
Mikawa
Y.
,
Zuo
L.
,
Chen
E.
,
Krumlauf
R.
,
Brenner
S.
(
1997
)
Organization of the Fugu rubripes Hox clusters, evidence for continuing evolution of vertebrate Hox complexes.
Nature Genetics
16
,
79
84
Barnes
S. N.
(
1971
)
Fine structure of the photoreceptor and cerebral ganglion of the tadpole larva of Amaroucium constellatum (Verrill) (Subphylum: Urochordata; Class: Ascidiacea).
Z. Zellforsch
117
,
1
16
Beachy
P. A.
,
Helfand
S. L.
,
Hogness
D. S.
(
1985
)
Segmental distribution of bithorax complex proteins during Drosophila development.
Nature
313
,
545
551
Boncinelli
E.
,
Somma
R.
,
Acampora
D.
,
Pannese
M.
,
D'Esposito
M.
,
Faiella
A.
,
Simeone
A.
(
1988
)
Organization of human homeobox genes.
Human Reprod
3
,
880
886
Burgtorf
C.
,
Welzel
K.
,
Hasenbank
R.
,
Zehetner
G.
,
Weis
S.
,
Lehrach
H.
(
1998
)
Gridded genomic libraries of different chordate species: a reference library system for basic and comparative genetic studies of chordate genomes.
Genomics
52
,
230
232
Caracciolo
A.
,
Gesualdo
I.
,
Branno
M.
,
Aniello
F.
,
Di Lauro
R.
,
Palumbo
A.
(
1997
)
Specific cellular localization of tyrosinase mRNA during Ciona intestinalis larval development.
Dev. Growth Differ
39
,
437
444
Carpenter
E. M.
,
Goddard
J. M.
,
Chisaka
O.
,
Manley
N. R.
,
Capecchi
M. R.
(
1993
).
Loss of Hoxa-1 (Hox-1.6) function results in the reorganization of the murine hindbrain.
Development
118
,
1063
1075
Chomczynski
P.
,
Sacchi
N.
(
1987
)
Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.
Anal. Biochem
162
,
156
159
Corbo
J. C.
,
Erives
A.
,
Di Gregorio
A.
,
Chang
A.
,
Levine
M.
(
1997
)
Dorsoventral patterning of the vertebrate neural tube is conserved in a protochordate.
Development
124
,
2335
2344
Corbo
J. C.
,
Levine
M.
,
Zeller
R. W.
(
1997
)
Characterization of a notochord-specific enhancer from the Brachyury promoter region of the ascidian, Cionaintestinalis.
Development
124
,
589
602
Di Gregorio
A.
,
Spagnuolo
A.
,
Ristoratore
F.
,
Pischetola
M.
,
Aniello
F.
,
Branno
M.
,
Cariello
L.
,
Di Lauro
R.
(
1995
)
Cloning of ascidian homeobox genes provides evidence for a primordial chordate cluster.
Gene
156
,
253
257
Di Gregorio
A.
,
Villani
M. G.
,
Locascio
A.
,
Ristoratore
F.
,
Aniello
F.
,
Branno
M.
(
1998
)
Developmental regulation and tissue-specific localization of calmodulin mRNA in the protochordate Ciona intestinalis.
Dev. Growth Diff
40
,
387
394
Duboule
D.
(
1993
)
The function of Hox genes in the morphogenesis of the vertebrate limb.
Ann. Genet
36
,
24
9
Duboule
D.
,
Dolle
P.
(
1989
)
The structural and functional organization of the murine Hox gene family resembles that of Drosophila homeotic genes.
EMBO J
8
,
1497
1505
Field
K. G.
,
Olsen
G. J.
,
Lane
D. J.
,
Giovannoni
S. J.
,
Ghiselin
M. T.
,
Raff
E. C.
,
Pace
N. R.
,
Raff
R. A.
(
1988
)
Molecular phylogeny of the animal kingdom.
Science
239
,
748
753
Gellon
G.
,
McGinnis
W.
(
1998
)
Shaping animal body plans in development and evolution by modulation of Hox expression patterns.
BioEssays
20
,
116
125
Glardon
S.
,
Callaerts
P.
,
Halder
G.
,
Gehring
W. J.
(
1997
)
Conservation of Pax −6 in a lower chordate, the ascidian Phallusia mammillata.
Development
124
,
817
825
Gould
A.
,
Morrison
A.
,
Sproat
G.
,
White
R.
,
Krumlauf
R.
(
1997
)
Positive cross-regulation and enhancer sharing: two mechanisms for specifying overlapping Hox expression patterns.
Genes Dev
11
,
900
913
Graham
A.
,
Papalopulu
N.
,
Krumlauf
R.
(
1989
)
The murine and Drosophila homeobox clusters have common features of organisation and expression.
Cell
57
,
367
378
Holland
P. W. H.
(
1992
)
Homeobox genes in vertebrate evolution.
BioEssays
14
,
267
273
Holland
P. W. H.
,
Garcia-Fernandez
J.
,
Williams
N. A.
,
Sidow
A.
(
1994
)
Gene duplications and the origins of vertebrate development.
Development
1994
,
125
133
Holland
P. W. H.
,
Holland
L. Z.
,
Williams
N. A.
,
Holland
N. D.
(
1992
)
An amphioxus homeobox gene: sequence conservation, spatialexpression during development and insights into vertebrate evolution.
Development
116
,
653
661
Hunt
P.
,
Gulisano
M.
,
Cook
M.
,
Sham
M.
,
Faiella
A.
,
Wilkinson
D.
,
Boncinelli
E.
,
Krumlauf
R.
(
1991
)
A distinct Hox code for the branchial region of the head.
Nature
353
,
861
864
Katsuyama
Y.
,
Wada
S.
,
Yasugi
S.
,
Saiga
H.
(
1995
)
Expression of the labial group Hox gene HrHox- 1 and its alteration induced by retinoic acid in development of the ascidian Halocynthia roretzi.
Development
121
,
3197
3205
Keynes
R.
,
Krumlauf
R.
(
1994
)
Hox genes and regionalization of the nervous system.
Ann. Rev. Neurosci
17
,
109
132
Krumlauf
R.
(
1994
)
Hox genes in vertebrate development.
Cell
78
,
191
201
Lewis
E. B.
(
1978
)
A gene complex controlling segmentation in Drosophila.
Nature
276
,
565
570
Lufkin
T.
(
1996
)
Transcriptional control of Hox genes in the vertebrate nervous system.
Curr. Opin. Gen. Dev
6
,
575
580
Lumsden
A.
(
1990
)
The cellular basis of segmentation in the developing hindbrain.
Trends Neurosci
13
,
329
335
Lumsden
A.
,
Krumlauf
R.
(
1996
)
Patterning the vertebrate neuraxis.
Science
274
,
1109
1115
Maconochie
M. K.
,
Nonchev
S.
,
Morrison
A.
,
Krumlauf
R.
(
1996
)
Paralogous Hox Genes: Function and Regulation.
Annu. Rev. Genet
30
,
529
556
Manzanares
M.
,
Cordes
S.
,
Ariza-McNaughton
L.
,
Sadl
V.
,
Maruthainer
K.
,
Barsh
G.
,
Krumlauf
R.
(
1999
)
Conserved and divergent roles of kreisler in regulation of the paralogous Hoxa3 and Hoxb3 genes.
Development
126
,
759
769
Manzanares
M.
,
Cordes
S.
,
Kwan
C.-T.
,
Sham
M. H.
,
Barsh
G. S.
,
Krumlauf
R.
(
1997
)
Segmental regulation of Hoxb-3 by kreisler.
Nature
387
,
191
195
Mark
M.
,
Lufkin
T.
,
Vonesch
J.-L.
,
Ruberte
E.
,
Olivo
J.-C.
,
Dolle
P.
,
Gorry
P.
,
Lumsden
A.
,
Chambon
P.
(
1993
)
Two rhombomeres are altered in Hoxa-1 mutant mice.
Development
119
,
319
338
Marshall
H.
,
Nonchev
S.
,
Sham
M. H.
,
Muchamore
I.
,
Lumsden
A.
,
Krumlauf
R.
(
1992
)
Retinoic acid alters hindbrain Hox code and induces transformation of rhombomeres 2/3 into a 4/5 identity.
Nature
360
,
737
741
McGinnis
W.
,
Krumlauf
R.
(
1992
)
Homeobox genes and axial patterning.
Cell
68
,
283
302
Nicol
D.
,
Meinertzhagen
I. A.
(
1991
)
Cell counts and maps in the larval central nervous system of the ascidian Ciona intestinalis (L).
J. Comp. Neurol
309
,
415
429
Popperl
H.
,
Bienz
M.
,
Studer
M.
,
Chan
S.-K.
,
Aparicio
S.
,
Brenner
S.
,
Mann
R. S.
,
Krumlauf
R.
(
1995
)
Segmental expression of Hoxb-1 is controlled by a highly conserved autoregulatory loop dependent upon exd/pbx.
Cell
81
,
1031
1042
Rubenstein
J. L.
,
Puelles
L.
(
1994
)
Homeobox gene expression during development of the vertebrate brain.
Curr. Top. Dev. Biol
29
,
1
63
Schugart
K.
,
Kappen
C.
,
Ruddle
F. H.
(
1988
)
Mammalian homeobox-containing genes: genome organization, structure, expression and evolution.
Br. J. Cancer
58
,
9
13
Sham
M. H.
,
Hunt
P.
,
Nonchev
S.
,
Papalopulu
N.
,
Graham
A.
,
Boncinelli
E.
,
Krumlauf
R.
(
1992
).
Analysis of the murine Hox 2.7 gene: conserved alternative transcripts with differential distribution in the nervous system and the potential for shared regulatory regions.
EMBO J
11
,
1825
1836
Studer
M.
,
Gavalas
A.
,
Marshall
H.
,
Ariza-McNaughton
L.
,
Rijli
F.
,
Chambon
P.
,
Krumlauf
R.
(
1998
)
Genetic interaction between Hoxa1 and Hoxb1 reveal new roles in regulation of early hindbrain patterning.
Development
125
,
1025
1036
Studer
M.
,
Lumsden
A.
,
Ariza-McNaughton
L.
,
Bradley
A.
,
Krumlauf
R.
(
1996
)
Altered segmental identity and abnormal migration of motor neurons in mice lacking Hox b-1.
Nature
384
,
630
635
Tiret
L.
,
Le Mouelic
H.
,
Maury
M.
,
Brulet
P.
(
1998
)
Increased apoptosis of motoneurons and altered somatotopic maps in the branchial spinal cord of Hox c8-deficient mice.
Development
125
,
279
291
Tomlinson
C. R.
,
Kozlowski
M. T.
,
Krein
W. H.
(
1990
)
Ectoderm nuclei from sea urchin embryos contain a spec-DNA binding protein similar to the vertebrate transcription factor USF.
Development
110
,
259
272
Wada
H.
,
Holland
P. W. H.
,
Sato
S.
,
Yamamoto
H.
,
Satoh
N.
(
1997
)
Neural tube is partially dorsalized by overexpression of HrPax −37: the ascidian homologue of Pax −3 and Pax −7.
Dev. Biol
187
,
240
252
Wada
H.
,
Saiga
H.
,
Satoh
N.
,
Holland
P. W. H.
(
1998
)
Tripartite organization of the ancestral chordate brain and the antiquity of placodes: insights from ascidian Pax −2/5/8, Hox and Otx genes.
Development
125
,
1113
1122
Whiting
J.
,
Marshall
H.
,
Cook
M.
,
Krumlauf
R.
,
Rigby
P. W. J.
,
Stott
D.
,
Allemann
R. K.
(
1991
).
Multiple spatially specific enhancers arerequired to reconstruct the pattern of Hox-2.6 gene expression.
Genes Dev
5
,
2048
2059
Yee
S.-P.
,
Rigby
P. W. J.
(
1993
)
The regulation of myogenin gene expression during the embryonic development of the mouse.
Genes Dev
7
,
1277
1289
Yuh
C.-H.
,
Ransick
A.
,
Martinez
P.
,
Britten
R. J.
,
Davidson
E. H.
(
1994
)
Complexity and organization of DNA-protein interactions in the 5′-regulatory region of an endoderm-specific marker gene in the sea urchin embryo.
Mech. Dev
47
,
165
186
This content is only available via PDF.