cDNA sequence analysis, gene expression and protein localisation of the inhibin α-subunit of Australian brushtail possum (Trichosurus vulpecula)

Abstract

An inhibin α-subunit cDNA sequence from the Australian brushtail possum (Trichosurus vulpecula) has been identified and analysed. The cDNA includes an open reading frame encoding a predicted precursor protein of 361 amino acids. The predicted protein sequence includes four possible proteolytic cleavage sites, 12 evolutionarily conserved cysteine residues and three potential N-linked glycosylation sites. The mature α-subunit is the carboxyl terminal fragment (αC) consisting of 131 amino acids. The full-length precursor protein shows a mean identify with eutherian homologues of 69.8%. The homology is not evenly distributed, with the putative αC fragment showing the highest level (79.7%). Using Northern hybridisation, an α- subunit transcript of approximately 1.6 kb was detected in adult possum ovary. Using in situ hybridisation and immunocytochemistry, inhibin α- subunit was localised exclusively to the granulosa cell layers of follicles. Hybridisation and immunostaining for the inhibin α-subunit were first observed in granulosa cells of primary follicles and the expression continued throughout all stages of follicular growth. Inhibin α-subunit mRNA and protein were also detected in cells of the corpus luteum. In summary, results indicate considerable conservation of the structure and possible function of the inhibin α-subunit protein since the divergence of the marsupial and eutherian mammalian lineages. The expression data suggest that, in the adult possum, inhibin may have a role in ovarian follicular growth from the primary stage of development.