Entactin and laminin gamma 1-chain gene expression in the early chick embryo

The expression patterns of entactin and laminin gamma1 chain genes were examined by in situ hybridization of their mRNAs in the early chick embryo from stage X (morula) to stage HH10-11 (10-somites). The entactin and laminin gamma1 transcripts were found in abundance in the embryo at stage X. Entactin polypeptides were detected in embryos at stage X by immunoprecipitation. The expression of the laminin transcripts was intense and of entactin milder in the epiblast and in the hypoblast of embryos at stage XIII (blastula). During gastrulation (stage HH3-4), the laminin gamma1 and entactin cRNAs gave strong signals in the cells ingressing through the primitive streak, in the migrating mesenchymal cells and the cells of the lower layer. At the neurula stage (stage HH5-6), punctate groups of cells expressed laminin gamma1 strongly in the neural ectoderm, while the signal of expression was milder and more uniform in chordamesoderm. The entactin cRNAs gave a strong punctate pattern of mRNA expression in the neural ectoderm, in mesoderm and in endoderm in embryos at the late gastrula stage (HH4), but mRNA expression was mild in the neural plate and in mesoderm and gave no signal in endoderm and lateral ectoderm in embryos at stage HH6 (neurula). At the 10-somite stage, the laminin gamma1 cRNAs gave strong signals in the neural tube and in neural crest cells migrating along the neural tube ventrally and low signals in ectoderm, intense signals in the myotome and milder signals in the dermatome and sclerotome of somites and intense signals in the mesonephric tubules. The punctate pattern of entactin expression was notable in cells at all stages studied. Ubiquitous expression of laminin gamma1 and entactin genes during the morula and blastula stages becomes restricted to specific cell populations as the first cell commitments start.