The vasopressin (VP) gene is expressed as three different transcripts in the rat testis. Using polymerase chain reaction (PCR) analysis we have been able to identify a VP RNA that is identical in exonic structure to that found in the hypothalamus. However, the abundance of this form is very low, and it cannot be detected by Northern blotting. Two VP RNAs with a novel structure, as shown using exon-specific probes, are present in higher abundance. By differential hybridization, sequencing of a cDNA clone, and PCR we have deduced the structure of these novel transcripts. Both of the novel testicular VP RNA species share two exons with the classical hypothalamic RNA. However, the testicular VP gene-derived RNA lacks the first exon of the hypothalamic transcript, the exon that contains the sequence information for the VP nonopeptide hormone. Instead, it has novel sequence that are derived from at least two unique testis-specific exons, one of which is located 7-10 kilobase up-stream of the brain-specific start of transcription. These two unusual transcripts are probably derived by alternative splicing of at least two up-stream exons. Sequence and polysome analyses indicate that the testicular VP RNAs are probably not translated. Northern blotting revealed that the VP gene-derived RNA species are tightly regulated during postnatal development, becoming apparent by 40 days of age, although they subsequently fail to respond to a variety of physiological perturbations. Oxytocin gene transcripts are not detectable by Northern hybridization, but the authentic hypothalamic-type RNA can be detected in the rat testis using PCR analysis.

We are using transgenic mice to study the regulation of the bovine vasopressin (VP) and oxytocin (OT) genes. Prompted by the observation that mice bearing a bovine OT transgene express bovine OT RNA in their testes, we investigated the expression of the VP-OT locus in normal mice and cattle. Normal wild-type mice do not have detectable levels of either VP or OT RNA in their testes. Normal cattle are also devoid of detectable VP transcripts, but have relatively high levels of testicular OT RNA. Additionally, OT, but not VP, peptide is detectable by HPLC. In situ hybridization to RNA in bovine testicular tissue sections localized OT transcripts to seminiferous tubules, with a distribution similar to that of alpha-inhibin, suggesting expression in Sertoli cells. Interestingly, the bovine OT RNAs in the transgenic mouse testes were also shown by in situ hybridization to have the same distribution. These data suggest that the cis-acting regulatory sequences responsible for expression of the OT gene in bovine Sertoli testis reside within the limits of the transgene used in this study. Further, the trans-acting factors present in murine testicular cells are able to recognize these elements, although they do not express the endogenous mouse OT gene in this tissue.

Fibrosing cholestatic hepatitis (FCH) is a rapidly progressive form of viral hepatitis B that occurs in severely immunosuppressed patients. Pathologically, the liver in FCH is characterized by widespread hepatocyte vacuolization and apoptosis, which, in contrast to more common forms of hepatitis B, is only rarely associated with significant inflammation. Therefore, it has been proposed that, in FCH, hepatocytes may be injured by a direct cytopathic effect of the virus rather than by the host immune response. In support of this hypothesis, we present evidence that cultured hepatoma cells that had been transfected with a plasmid selectively expressing the viral large surface protein form numerous large vacuoles and undergo apoptosis. The similarity of the cytopathology in FCH in vivo and in these transfected cells in vitro strongly implicates the large surface protein as the direct cause of this acute liver disease. This conclusion is further supported by the published demonstration that hepatocytes tend to accumulate large surface protein in FCH, which may reflect its overexpression by the virus. In conclusion, our data implicate the large surface protein as a major cause of hepatocyte injury in fibrosing cholestatic hepatitis.