Variation in gene transcript profiles of two V1a-type arginine vasotocin receptors among sexual phases of bluehead wrasse (Thalassoma bifasciatum).

The neurohypophyseal hormone arginine vasotocin (AVT) mediates behavioral and reproductive plasticity in vertebrates, and has been linked to the behavioral changes associated with protogyny in the bluehead wrasse (Thalassoma bifasciatum). In this study, we sequenced full-length cDNAs encoding two distinct V1a-type AVT receptors (v1a1 and v1a2) from the bluehead wrasse, and examined variation in brain and gonadal abundance of these receptor transcripts among sexual phases. End point RT-PCR revealed that v1a1 and v1a2 transcripts varied in tissue distribution, with v1a1 receptor mRNAs at greatest levels in the telencephalon, hypothalamus, optic tectum, cerebellum and testis, and v1a2 receptor transcripts most abundant in the hypothalamus, cerebellum and gills. In the brain, v1a1 and v1a2 mRNAs both localized by in situ hybridization to the dorsal and ventral telencephalon, the preoptic area of the hypothalamus, the ventral hypothalamus and lateral recess of the third ventricle. Quantitative real-time RT-PCR revealed that relative abundance of these two receptor mRNAs varied significantly in brain and gonad with sexual phase. Relative levels of v1a2 mRNAs were greater in whole brain and isolated hypothalamus of terminal phase (TP) male wrasse compared to initial phase (IP) males or females. In the gonad, v1a1 mRNAs were at levels 2.5-fold greater in the testes of IP males - and 4-5-fold greater in the testes of TP males - compared to the ovaries of females. These results provide evidence that V1a-type AVT receptor transcript abundance in the hypothalamus and gonads of bluehead wrasse varies in patterns linked to sexual phase, and bestow a foundation for future studies investigating how differential expression of v1a1 and v1a2 teleost AVT receptors links to behavioral status and gonadal function in fish more broadly.