T. Stratford et al., Abnormal anteroposterior and dorsoventral patterning of the limb bud in the absence of retinoids, MECH DEVEL, 81(1-2), 1999, pp. 115-125
We describe here how the early limb bud of the quail embryo develops in the
absence of retinoids, including retinoic acid. Retinoid-deficient embryos
develop to about stage 20/21, thus allowing patterns of early gene activity
in the limb bud to be readily examined. Genes representing different aspec
ts of limb polarity were analysed. Concerning the anteroposterior axis, Hox
b-8 was up-regulated and its border was shifted anteriorly whereas shh and
the mesodermal expression of bmp-2 were down-regulated in the absence of re
tinoids. Concerning the apical ectodermal genes, fgf-4 was down-regulated w
hereas fgf-8 and the ectodermal domain of bmp-a were unaffected. Genes invo
lved in dorsoventral polarity were all disrupted. Wnt-7a, normally confined
to the dorsal ectoderm, was ectopically expressed in the ventral ectoderm
and the corresponding dorsal mesodermal gene Lmx-1 spread into the ventral
mesoderm. En-1 was partially or completely absent from the ventral ectoderm
, These dorsoventral patterns of expression resemble those seen in En-l kno
ckout mouse limb buds. Overall, the patterns of gene expression are also si
milar to the Japanese limbless mutant. These experiments demonstrate that t
he retinoid-deficient embryo is a valuable tool for dissecting pathways of
gene activity in the limb bud and reveal for the first time a role for reti
noic acid in the organisation of the dorsoventral axis. (C) 1999 Elsevier S
cience Ireland Ltd. All rights reserved.