PATTERNS OF GENE-EXPRESSION IN THE CORE OF SPEMANNS ORGANIZER AND ACTIVIN-TREATED ECTODERM IN CYNOPS-PYRRHOGASTER

The presumptive pharyngeal endoderm region of the Cynops early gastrul a induces head or trunk-tail structures in sandwich culture. Activin-t reated ectoderm can mimic this phenomenon at least at the histological level. The patterns of expression of organizer-specific genes were ex amined to compare these two inductive materials at the molecular level . A chordin cDNA clone from Cynops pyrrhogaster (Cychd) was isolated b y reverse transcription-polymerase chain reaction (RT-PCR). Cychd mRNA was first detected in the presumptive pharyngeal endoderm and prechor dal plate regions oi stage 11 embryos, and was expressed continuously until stage 20. The spatiotemporal expression pattern of Cychd was sim ilar to that of Xenopus chordin. The patterns of expression of organiz er-related genes in the pharyngeal endoderm and activin-treated ectode rm were compared by RT-PCR analysis. Expression of Cychd in these two materials peaked at the time when they can induce head structures in s andwich culture. Expression of fork head and goosecoid did not change in the presumptive pharyngeal endoderm over this period. Cychd may pla y a key role in head formation in the Cychd embryo.