In situ localization of two prolactin-related messenger ribonucleic acids to binucleate cells of bovine placentomes.

The bovine fetal placenta expresses a family of PRL-related genes, consisting of the gene encoding bovine placental lactogen (bPL), and a diverse group of related genes, exemplified by bovine PRL-related cDNA I (bPRCI). bPL and the protein encoded by bPRCI are quite distinct from one another, predicting proteins only about 36% similar in amino acid sequence. To identify the cells responsible for the expression of bPL and bPRCI, in situ hybridization experiments were performed. 35S-Labeled RNA probes were prepared from the 3' regions of bPL and bPRCI and allowed to hybridize to frozen sections of bovine placentomes. Transcripts corresponding to bPL and bPRCI colocalized to fetal binucleate cells, which is consistent with the immunocytochemical localization of bPL. Signal from radiolabeled antisense strand probe was blocked by pretreatment of the sections with a 150-fold excess of unlabeled probe, but not by an excess of unlabeled probe prepared using the other cDNA as a template. This demonstrated that the signals observed were specific for bPL and bPRCI and that the two probes did not cross-hybridize at the stringency of our conditions. Radiolabeled sense strand probes yielded no signal. We conclude that the binucleate cells of the bovine placenta transcribe at least two members of the PRL gene family that may influence fetal development and maternal adaptation to pregnancy.