Homeobox genes are important in the regulation of outgrowth and pattern formation during limb development. It is likely that homeobox genes play an equally important role during limb regeneration. We have isolated and identified 17 different homeobox-containing genes expressed by cells of regenerating axolotl limbs. Of these, nearly half of the clones represent genes belonging to the HoxA complex, which are thought to be involved in pattern formation along the proximal-distal limb axis. In this paper we report on the expression patterns of two 5′ members of this complex, HoxA13 and HoxA9. These genes are expressed in cells of developing limb buds and regenerating blastemas. The pattern of expression in developing axolotl limb buds is comparable to that in mouse and chick limb buds; the expression domain of HoxA13 is more distally restricted than that of HoxA9. As in developing mouse and chick limbs, HoxA13 likely functions in the specification of distal limb structures, and HoxA9 in the specification of more proximal structures. In contrast, during regeneration, HoxA13 and HoxA9 do not follow the rule of spatial colinearity observed in developing limbs. Instead, both genes are initially expressed in the same population of stump cells, giving them a distal Hox code regardless of the level of amputation. In addition, both are reexpressed within 24 hours after amputation, suggesting that reexpression may be synchronous rather than temporally colinear. Treatment with retinoic acid alters this Hox code to that of a more proximal region by the rapid and differential downregulation of HoxA13, at the same time that expression of HoxA9 is unaffected. HoxA reexpression occurs prior to blastema formation, 24–48 hours after amputation, and is an early molecular marker for dedifferentiation.

Reference

Auffray
C.
,
Rougeon
F.
(
1980
)
Purification of mouse immunoglobulin heavy-chain messenger RNAs from total myeloma tumor RNA.
Eur. J. Biochem
107
,
303
314
Blumberg
B.
,
Wright
C. V. E.
,
De Robertis
E. M.
,
Cho
K. W. Y.
(
1991
)
Organizer-specific homeobox genes in Xenopus laevis embryos.
Science
253
,
194
196
Brown
R.
,
Brockes
J. P.
(
1991
)
Identification and expression of a regeneration-specific homeobox gene in the newt limb blastema.
Development
111
,
489
496
Bryant
S. V.
,
Gardiner
D. M.
(
1992
)
Retinoic acid, local cell-cell interactions, and pattern formation in vertebrate limbs.
Dev. Biol
152
,
1
25
Burglin
T. R.
,
Finney
M.
,
Coulson
A.
,
Ruvkun
G.
(
1989
)
Caenorhabditis elegans has scores of homoeobox-containing genes.
Nature
341
,
239
243
Charite
J.
,
de Graaff
W.
,
Shen
S.
,
Deschamps
J.
(
1994
)
Ectopic expression of Hoxb-8 causes duplication of the ZPA in the forelimb and homeotic transformation of axial structures.
Cell
78
,
589
601
Davis
A. P.
,
Capecchi
M. R.
(
1994
)
Axial homeosis and appendicular skeleton defects in mice with a targeted disruption of Hoxd-11.
Development
120
,
2187
2198
Dolle
P.
,
Dierich
A.
,
LeMeur
M.
,
Schimmang
T.
,
Schuhbaur
B.
,
Chambon
P.
,
Duboule
D.
(
1993
)
Disruption of Hoxd-13 gene induces localized heterochrony leading to mice with neotenic limbs.
Cell
75
,
431
441
Dolle
P.
,
Izpisúa-Belmonte
J.-C.
,
Falkenstein
H.
,
Renucci
A.
,
Duboule
D.
(
1989
)
Coordinate expression of the murine Hox-5 complex homoeobox-containing genes during limb pattern formation.
Nature
342
,
767
772
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
Gehring
W. J.
,
Affolter
M.
,
Burglin
T.
(
1994
)
Homeodomain proteins.
Ann. Rev. Biochem
63
,
487
526
Graham
A.
,
Papalopulu
N.
,
Krumlauf
R.
(
1989
)
The murine and Drosophila homeobox gene complexes have common features of organization and expression.
Cell
57
,
367
378
Haack
H.
,
Gruss
P.
(
1993
)
The establishment of murine Hox-1 expression domains during patterning of the limb.
Dev. Biol
157
,
410
422
Hayamizu
T. F.
,
Bryant
S. V.
(
1994
)
Reciprocal changes in Hox D13 and RAR-2 expression in response to retinoic acid in chick limb buds.
Dev. Biol
166
,
123
132
Izpisúa-Belmonte
J.-C.
,
Duboule
D.
(
1992
)
Homeobox genes and pattern formation in the vertebrate limb.
Dev. Biol
152
,
26
36
Izpisúa-Belmonte
J.-C.
,
Tickle
C.
,
Dolle
P.
,
Wolpert
L.
,
Duboule
D.
(
1991
)
Expression of the homeobox Hox-4 genes and the specification of position in chick wing development.
Nature
350
,
585
589
Kessel
M.
,
Gruss
P.
(
1991
)
Homeotic transformations of murine vertebrae and concomitant alteration of Hox codes induced by retinoic acid.
Cell
67
,
89
104
Krumlauf
R.
(
1993
)
Mouse Hox genetic functions.
Curr. Opin. Genet. Dev
3
,
621
625
Krumlauf
R.
(
1994
)
Hox genes in vertebrate development.
Cell
78
,
191
201
Lamb
T. M.
,
Knecht
A. K.
,
Smith
W. C.
,
Stachel
S. E.
,
Economides
A. N.
,
Stahl
N.
,
Yancopolous
G. D.
,
Harland
R. M.
(
1993
)
Neural induction by the secreted polypeptide noggin.
Science
262
,
713
718
Maden
M.
(
1982
)
Vitamin A and pattern formation in the regenerating limb.
Nature
295
,
672
675
Mavilio
F.
(
1993
)
Regulation of vertebrate homeobox-containing genes by morphogens.
Europ. J. Biochem
212
,
273
288
Morgan
B. A.
,
Izpisúa-Belmonte
J.-C.
,
Duboule
D.
,
Tabin
C. J.
(
1992
).
Targeted misexpression of Hox-4.6 in the avian limb bud causes apparent homeotic transformations.
Nature
358
,
236
239
Muneoka
K.
,
Sassoon
D.
(
1992
)
Limb development and regeneration.
Dev. Biol
152
,
37
49
Nohno
T.
,
Noji
S.
,
Koyama
E.
,
Ohyama
K.
,
Myokai
F.
,
Kuroiwa
A.
,
Saito
T.
,
Taniguchi
S.
(
1991
)
Involvement of the Chox-4 chicken homeobox genes in determination of anteroposterior axial polarity during limb development.
Cell
64
,
1197
1205
Savard
P.
,
Gates
P. B.
,
Brockes
J. P.
(
1988
)
Position dependent expression of a homeobox gene transcript in relation to amphibian limb regeneration.
EMBO J
7
,
4275
4282
Simeone
A.
,
Acampora
D.
,
Nigro
V.
,
Faiella
A.
,
D'Esposito
M.
,
Stornaiuolo
A.
,
Mavilio
F.
,
Boncinelli
E.
(
1991
)
Differential regulation by retinoic acid of the homeobox genes of the four HOX loci in human embryonal carcinoma cells.
Mech. Dev
33
,
215
228
Simon
H.-G.
,
Tabin
C. J.
(
1993
).
Analysis of Hox-4.5 and Hox-3.6 expression during newt limb regeneration: differential regulation of paralagous Hox genes suggest different roles for members of different Hox clusters.
Development
117
,
1397
1407
Small
K. M.
,
Potter
S. S.
(
1993
)
Homeotic transformations and limb defects in Hox A11 mutant mice.
Genes Dev
7
,
2318
2328
Tabin
C. J.
(
1989
)
Isolation of potential vertebrate limb-identity genes.
Development
105
,
813
820
Yokouchi
Y.
,
Sasaki
H.
,
Kuroiwa
A.
(
1991
)
Homeobox gene expression correlated with the bifurcation process of limb cartilage development.
Nature
353
,
443
445
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