DIFFERENTIAL EXPRESSION OF BMP RECEPTORS IN EARLY MOUSE DEVELOPMENT

Bone morphogenetic proteins (BMPs) are members of the transforming gro wth factor-beta family of polypeptide signaling molecules. They functi on via binding to two types of transmembrane serine/threonine kinase r eceptors, type I and type II receptors, that are both necessary for si gnaling. The expression patterns of the type II BMP receptor (BMPR-II) and three type I BMP receptors (ActR-I, BMPR-IA and BMPR-IB) were exa mined in preimplantation embryos by means of heminested reverse transc ription-polymerase chain reaction (RT-PCR). BMPR-II mRNA was detected in one-cell, two-cell and blastocyst stage embryos. ActR-I exhibited a similar expression pattern. BMPR-IA mRNA however was only detected in blastocysts, whereas BMPR-IB transcripts were detected at all stages from the one-cell zygote to the uncompacted morula, but not in the com pacted morula and blastocyst. If translated into proteins, this sugges ts that different receptor complexes can be formed at different develo pmental stages. Transcripts for BM Ps were not detected in preimplanta tion embryos, but were detected in the maternal tissues surrounding th e embryos. BMPR-II, BMPR-IA and BMPR-IB mRNAs were also detected in un differentiated and differentiated embryonal carcinoma and embryonic st em cells. In postimplantation embryos BMPR-II transcripts were first d etected from 6.0 days post coitum. In situ hybridization analysis reve aled that BMPR-II mRNA is ubiquitously expressed in the entire embryo at least until midgestation.