Coordinated expression of 3 ' Hox genes during murine embryonal gut development: An enteric Hox code

Background & Aims: Hox genes are highly conserved developmental control gen es that may be organized and expressed in the form of a code required for c orrect morphogenesis, Little is known about their control of the embryonal gut. However, Hox paralogues 4 and 5, which are expressed at the sites of o rigin of vagal neural crest cells and splanchnic mesoderm, are likely to be important. We have studied the expression domains of these genes in the gu t both spatially and temporally, Methods: CD1 mice embryos of embryonic day s E8.5-E17.5 were studied. The spatial and temporal expression patterns of messenger RNA of Hoxa4, b4, c4, d4, a5, c5, and b5 homeoprotein were determ ined by in situ hybridization and immunohistochemistry in whole embryos, wh ole gastrointestinal tracts, and vibratome sections. Results: There were di fferent spatial, temporal, and combinatorial expression patterns in differe nt morphological regions: foregut, prececal gut, cecum, and postcecal gut. Two dynamic gradients, rostral and caudal, were coordinated with nested exp ression domains along the gut primordium, Region-specific domains were pres ent in the stomach and cecum, Conclusions: The expression patterns of genes in paralogous groups 4 and 5 suggest that they are organized to form a spe cific enteric Hox code required for correct enteric development.