Differential distribution of mRNA for the α- and β-subunits of chorionic gonadotrophin in the implantation stage blastocyst of the marmoset monkey

Abstract

We studied the expression of mRNA encoding the a- and β-subunts of marmoset chrrionic gonadotrophin (mCG) in implantation stage blastocysts and in a tropho-blastic cell line derived from such blastocysts. In this investigation in situ hybridization was carried out using digoxygenin-labelled riboprobes to localize the subunit transcripts. The trophoblastic cell line, known to secrete bioactive mCG, was used as a positive control. Marmoset uterine embryos were cultured to hatched blastocysts and following growth on Matrigel or plastic were processed for in situ hybridization at developmental stages ranging from 13–15 days post-conception. In serial sections mCG-β mRNA was detected mainly in polar, trophoblast. The mRNA for mCG-a was expressed more uniformly in polar and mural trophoblast. Transcripts for the β-subunit were not expressed, or present as weak signals, in the inner cell mass (ICM) and endoderm. However, low levels of mRNA for mCG-a were detected in the ICM and visceral endoderm. We have concluded that mRNA for mCG-β was primarily localized to patches of syncytiotrophoblast at the embryonic pole and sparsely distributed in mural trophoblast, while the transcripts for mCG-a were distributed more uniformly in differentiating cytotrophoblast and syncytium, and at much lower levels in ICM and early endoderm.