CHARACTERIZATION OF GERM CELL-SPECIFIC EXPRESSION OF THE ORPHAN NUCLEAR RECEPTOR, GERM-CELL NUCLEAR FACTOR

Nuclear receptors, such as those for androgens, estrogens, and progest erones, control many reproductive processes. Proteins with structures similar to these receptors, but for which ligands have not yet been id entified, have been termed orphan nuclear receptors. One of these orph ans, germ cell nuclear factor (GCNF), has been shown to be germ cell s pecific in the adult and, therefore, may also participate in the regul ation of reproductive functions. In this paper, we examine more closel y the expression patterns of GCNF in germ cells to begin to define spa tio-temporal domains of its activity. lit situ hybridization showed th at GCNF messenger RNA (mRNA) is lacking in the testis of hypogonadal m utant mice, which lack developed spermatids, but is present in the wil d-type testis. Thus, GCNF is, indeed, germ cell specific in the adult male. Quantitation of the specific in situ hybridization signal in wil d-type testis reveals that GCNF mRNA is most abundant in stage VII rou nd spermatids. Similarly, Northern analysis and specific in situ hybri dization show that GCNF expression first occurs in testis of 20-day-ol d mice, when round spermatids first emerge. Therefore, in the male, GC NF expression occurs postneiotically and may participate in the morpho logical changes of the maturing spermatids. In contrast, female expres sion of GCNF is shown in growing oocytes that have not completed the f irst meiotic division. Thus, GCNF in the female is expressed before th e completion of meiosis. Finally, the nature of the two different mRNA s that hybridize to the GCNF complementary DNA was studied. Although b oth messages contain the DNA binding domain, only the larger message i s recognized by a probe from the extreme 3' untranslated region. In si tu hybridization with these differential probes demonstrates that both messages are present in growing oocytes. In addition, the coding regi on and portions of the 3' untranslated region of the GCNF complementar y DNA are conserved in the rat.