Differential expression ofcSmad1 andcSmad5 in the primitive streak during chick embryo gastrulation

Whole mount in situ hybridization was performed to determine the expression patterns of cSmad1 and cSmad5 during gastrulation stages (Hamburger-Hamilton 2-6) of chicken embryogenesis. It was revealed that cSmads 1 and 5 mRNAs are prominently expressed in the developing primitive streak. As determined from cross-sectional analysis of stage 4 embryos, most transcripts were associated with the ingressing mesoderm. However, whereas cSmad5 was expressed throughout the streak at all stages examined, the strongest expression of cSmad1 was confined to the posterior half of the streak.