Expression of alternate growth hormone receptor messenger RNA in ovary and uterus of cattle

Growth hormone (GH) receptor mRNA is found within the corpus luteum and endometrium of cattle. However, binding sites for placental lactogen (PL) but not GH are found within these tissues. The objectives were to isolate cDNA for the GH receptor within the reproductive tissues of cattle and to examine these cDNA as potential variants of the GH receptor that bind PL. Ten cDNA clones were isolated from a bovine endometrial cDNA library with a ³²P- labeled cDNA of the GH receptor extracellular domain. On the basis of restriction enzyme digestion, 2 of the 10 cDNA clones contained exon 1. The DNA sequence of these clones was determined by dideoxy nucleotide sequencing. The exon I DNA sequence of each clone (exon 1B) was different from the previously reported exon I for the bovine GH receptor cDNA isolated from liver (exon 1A). Analyses of these cDNA sequences showed that exon lB contained significant homology with placental forms of the GH receptor found in mouse and human. Unlike the human cDNA, the bovine cDNA isolated from endometrium contained an intact third exon. Amplification of GH receptor mRNA by reverse transcriptase polymerase chain reaction, with exon 1A- and 1B- specific forward primers, showed that exon lB was expressed in liver, corpus luteum, ovary, endometrium, and myometrium. Exon 1A was found almost exclusively in liver, and little was found in reproductive tissues. The predicted initiation of protein coding for the GH receptor was within the second exon and was not changed by the splicing of the alternate first exon. This suggests that the alternate mRNA results in the expression of intact GH receptor protein that is similar to that found within liver. Alternative promoters (1B) may control the expression of the receptor outside the liver. Furthermore, mechanisms other than the differential splicing of GH receptor protein may dictate the specificity of PL binding within the endometrium and corpus luteum.