A subfamily of bovine prolactin-related transcripts distinct from placental lactogen in the fetal placenta.

The placentae of many species express genes homologous to the pituitary hormones. In the bovine, two transcripts distinct from the pituitary hormones have been previously described: bovine placental lactogen (bPL) and bovine prolactin-related cDNA I (bPRCI). Here we provide evidence for a subfamily of prolactin-related transcripts quite different from bPL and the rodent placental homologues, which include proliferin and rat prolactin-related proteins. Bovine prolactin-related cDNAs II and III (bPRCII and bPRCIII) are about 75% similar in nucleotide sequence to one another and bPRCI, but only 56% similar to bPL, and about 45% to the rodent placental transcripts. The deduced amino acid sequences follow a similar pattern: they are about 60% similar to one another, but only about 35% similar to bPL as well as the predicted rodent placental proteins. mRNA levels corresponding to bPL, bPRCI, and bPRCIII in the fetal placenta show distinct patterns. The role of these predicted hormones during pregnancy remains to be determined.