Isolation and characterisation of a cDNA encoding a zona pellucida protein(ZPB) from the marsupial Trichosurus vulpecula (brushtail possum)

We have cloned a cDNA containing the entire coding sequence of a marsupial (the brushtail possum, Trichosurus vulpecula) zona pellucida protein (ZPB). The open reading frame of 1,581 nt is predicted to encode a ZPB polypeptid e of 527 amino acids which contains 20 cysteine residues, 7 potential N-lin ked glycosylation sites, a potential N-terminal signal peptide and a potent ial C-terminal trans-membrane domain, preceded by a furin proteolytic proce ssing signal. Sequence comparisons between possum ZPB and orthologous polyp eptides from 7 eutherian species and from Xenopus laevis, reveal the existe nce of a high degree of sequence similarity, particularly in the central po rtion of the molecule. Cysteine residues are highly conserved, and all nine species possess potential N-terminal signal peptide sequences and C-termin al transmembrane domains of approximately the same length. In situ hybridis ation revealed that expression of ZPB was restricted to oocytes of primordi al and primary follicles of adult possums; no expression was detected in th e surrounding granulosa cells. The broad conservation of ZPB sequence, stru cture and expression over a wide range of mammalian species, revealed by ou r studies, makes it unlikely that these features account far the different properties of the marsupial and eutherian zona pellucidae. Mol. Reprod. Dev . 52:174-182, 1999. (C) 1999 Wiley-Liss, Inc.