EXPRESSION OF TRANSCRIPTION FACTOR HNF-4 IN THE EXTRAEMBRYONIC ENDODERM, GUT, AND NEPHROGENIC TISSUE OF THE DEVELOPING MOUSE EMBRYO - HNF-4IS A MARKER FOR PRIMARY ENDODERM IN THE IMPLANTING BLASTOCYST

The expression of HNF-4 (hepatocyte nuclear factor 4) mRNA in postimpl antation mouse embryos was analyzed by in situ hybridization. Expressi on was found in the primary endoderm at embryonic day 4.5 and was rest ricted to the columnar visceral endoderm cells of the yolk sac from da y 5.5 to day 8.5. HNF-4 mRNA was first detected in embryonic tissues a t day 8.5, in the liver diverticulum and the hindgut. At later times H NF-4 transcripts were observed in the mesonephric tubules, pancreas, s tomach, and intestine and, still later, in the metanephric tubules of the developing kidney. This expression pattern suggests that HNF-4 has a role in the earliest stages of murine postimplantation development as well as in organogenesis.