Formation of extra digits in the interdigital spaces of the chick leg bud is not preceded by changes in the expression of theMsxandHoxdgenes

摘要

By in situ hybridization we studied the expression patterns ofMsxandHoxdgenes during the late development of the chick leg autopodium (foot) and compared them to patterns during the experimental development of interdigital extra digits. Extra digits are induced in the third interdigital space after various experimental manipulations, such as transient isolation of the interdigit, or removal of the interdigital marginal ectoderm and mesoderm.Msx1andMsx2are normally expressed in the interdigital tissue programmed to die. Our experiment changes the fate of the interdigital tissue from cell death to chondrogenesis and provides a good model for studyingMsxinvolvement in defining areas of programmed cell death. Among the proposed roles forHoxdgenes is their involvement in the specification of digit identity early in development. The induction of extra digits allows us to examine whether this new morphogenetic commitment of the interdigital tissue involves changes in the domains of expression ofHoxdgenes. Our results show that extra digits develop without a previous modification of the normal pattern of expression ofMsxorHoxdgenes. This observation does not support the correlation between the expression ofMsxgenes and programmed cell death and suggests a role for these genes in maintaining the interdigital tissue in an undifferentiated state. Our results show that an increased number of digits can be formed without modifications in the pattern of expression of the 5′-locatedHoxdgenes and suggest the existence of latent or residual digit organization mechanisms past the time when digits are normally determined, independent ofHoxdgene expressio