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Pit-1/Growth Hormone Factor 1 Splice Variant Expression in the Rhesus Monkey Pituitary Gland and the Rhesus and Human Placenta¹

Department of Obstetrics and Gynecology (T.G.G.), University of Wisconsin Medical School; and Wisconsin Regional Primate Research Center (J.T.S., C.M.C., M.D., J.M.F., T.G.G.), University of Wisconsin, Madison, Wisconsin 53715-1299

Address correspondence and requests for reprints to: Dr. Thaddeus G. Golos, Ph.D., Wisconsin Regional Primate Research Center, 1223 Capitol Court, University of Wisconsin, Madison, Wisconsin 53715-1299. E-mail: golos{at}primate.wisc.edu

We have examined the expression of Pit-1 messenger RNA (mRNA) splice variants in the nonhuman primate pituitary and in rhesus and human placenta. Full-length complementary DNAs (cDNAs) representing Pit-1 and the Pit-1ß splice variants were cloned from a rhesus monkey pituitary cDNA library and were readily detectable by RT-PCR with rhesus pituitary gland RNA. The Pit-1T variant previously reported in mouse pituitary tumor cell lines was not detectable in normal rhesus pituitary tissue, although two novel splice variants were detected. A cDNA approximating the rat Pit-1 4 variant was cloned but coded for a truncated and presumably nonfunctional protein. Only by using a nested RT-PCR approach were Pit-1 and Pit-1ß variants consistently detectable in both human and rhesus placental tissue. The Pit-1ß variant mRNA was not detectable in JEG-3 choriocarcinoma cells unless the cells were stimulated with 8-Br-cAMP. Immunoblot studies with nuclear extracts from primary rhesus syncytiotrophoblast cultures or JEG-3 choriocarcinoma cells indicated that although mRNA levels were very low, Pit-1 protein was detectable in differentiated cytotrophoblasts, and levels increased after treatment with 8-Br-cAMP. Two major species of Pit-1 protein were detected that corresponded to the two major bands in rat pituitary GH3 cell nuclear extracts. Low levels of slightly larger bands also were seen, which may represent Pit-1ß protein or phosphorylated species. We conclude that Pit-1 splice variants expressed in the primate pituitary gland differ from those in the rodent gland and that the Pit-1 and Pit-1ß mRNAs expressed in the placenta give rise to a pattern of protein expression similar to that seen in pituitary cells, which is inducible by treatment with 8-Br-cAMP.

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