Vasopressin and oxytocin gene expression in rat testis

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.