CDNA SEQUENCE-ANALYSIS, GENE-EXPRESSION AND PROTEIN LOCALIZATION OF THE INHIBIN ALPHA-SUBUNIT OF AUSTRALIAN BRUSHTAIL POSSUM (TRICHOSURUS-VULPECULA)

An inhibin alpha-subunit cDNA sequence from the Australian brushtail p ossum (Trichosurus vulpecula) has been identified and analysed. The cD NA includes an open reading frame encoding a predicted precursor prote in of 361 amino acids. The predicted protein sequence includes four po ssible proteolytic cleavage sites, 12 evolutionarily conserved cystein e residues and three potential N-linked glycosylation sites. The matur e alpha-subunit is the carboxyl terminal fragment (alpha C) consisting of 131 amino acids. The full-length precursor protein shows a mean id entity with eutherian homologues of 69.8%. The homology is not evenly distributed, with the putative alpha C fragment showing the highest le vel (79.7%). Using Northern hybridisation, an alpha-subunit transcript of approximately 1.6 kb was detected in adult possum ovary. Using in situ hybridisation and immunocytochemistry, inhibin alpha-subunit was localised exclusively to the granulosa cell layers of follicles. Hybri disation and immunostaining for the inhibin alpha-subunit were first o bserved in granulosa cells of primary follicles and the expression con tinued throughout all stages of follicular growth. Inhibin alpha-subun it mRNA and protein were also detected in cells of the corpus luteum. In summary, results indicate considerable conservation of the structur e and possible function of the inhibin alpha-subunit protein since the divergence of the marsupial and eutherian mammalian lineages. The exp ression data suggest that, in the adult possum, inhibin may have a rol e in ovarian follicular growth from the primary stage of development.