Identification of a New Gene Expressed Specifically in Early Mouse Embryos: mouse embryo/gene expression/e5.5.

To identify genes involved in retinoic acid signaling during early embryogenesis, specifically during implantation and early postimplantation, cDNA libraries constructed from mouse embryos at e4.5 and e5.5, respectively, have been screened. Based upon DNA sequence homology, one clone has been isolated by using mouse retinoic acid receptor α (RAR_α) as the probe. This clone, designated as 80.3, is expressed in the embryonic portion at early egg cylinder stage, and is highly expressed in the entire embryo at e6.5. Its expression decreases in embryos older than e9.5 and can not be detected in any adult tissues. In vitro transcription/translation of this cDNA has produced a protein product with a molecular weight of approximately 50 kDa. The central to C‐terminal portion of this gene is highly homologous to a human orphan receptor, TR‐2. This homologous region contains a potential zinc‐finger DNA binding motif followed by a putative ligand‐binding domain. However, this gene is very different from TR2 in the N‐terminal region and appears to be a newly identified gene with a specific pattern of expression during early embryogenesis.