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 an d endometrium of cattle. However, binding sites for placental lactogen (PL) but not GH an found within these tissues. The objectives were to isolate cDNA for the GH receptor within the reproductive tissues of c attle and to examine these cDNA as potential variants of the GH recept or that bind FL. Ten cDNA clones were isolated from a bovine endometri al cDNA library with a P-32-labeled cDNA of the GH receptor extracellu lar domain. On the basis of restriction enzyme digestion, 2 of the 10 cDNA clones contained exon 1. The DNA sequence of these clones was det ermined by dideoxy nucleotide sequencing. The exon 1 DNA sequence of e ach clone (exon 1B) was different from the previously reported exon 1 for the bovine CH receptor cDNA isolated from liver (exon 1A). Analyse s of these cDNA sequences showed that exon IB contained significant ho mology with placental forms of the GH receptor found in mouse and huma n. Unlike the human cDNA, the bovine cDNA isolated from endometrium co ntained an intact third exon. Amplification of GH receptor mRNA by rev erse transcriptase polymerase chain reaction, with exon 1A- and 1B-spe cific forward primers, showed that exon 1B was expressed in liver, cor pus luteum, ovary, endometrium, and myometrium. Exon 1A was found almo st exclusively in liver, and little was found in reproductive tissues. The predicted initiation of protein coding for the GH receptor was wi thin the second exon and was not changed by the splicing of the altern ate first exon. This suggests that the alternate mRNA results in the e xpression 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 th e differential splicing of GH receptor protein may dictate the specifi city of PL binding within the endometrium and corpus luteum.