The limb defect in the mouse Hypodactyly (Hd) affects only the distal
structures. Heterozygotes (Hd/+) lack all or part of the distal phalan
x and the terminal claw of digit I on the hindlimbs; mice homozygous (
Hd/Hd) for the mutation have lust one digit on each of the four limbs.
Early limb development in the mutant appears normal and a change in m
orphology can only be detected later. Limb buds of Hd/+ and Hd/Hd embr
yos become reduced in width, with Hd/Hd buds becoming very pointed ins
tead of rounded. This change in bud shape is correlated with an increa
se in cell death anteriorly in Hd/+ hindlimbs and both anteriorly and
posteriorly in Hd/Hd fore- and hindlimb buds. The apical ectodermal ri
dge is very pronounced in pointed Hd/Hd limb buds. Mesenchyme cells fr
om the Hd/Hd mutant in culture show a cell-autonomous change in behavi
our and less cartilage differentiates. (C) 1996 Wiley-Liss, Inc.