Identification and spatial distribution of the mRNA encoding an egg envelope component of the Cyprinid zebrafish, Danio rerio, homologous to the mammalian ZP3(ZPC)

Using degenerate reverse transcription polymerase chain reaction (RT-PCR) t echniques we have isolated a cDNA encoding a putative component of the zebr afish Danio rerio egg chorion, homologous to the mammalian ZP3 (ZPC). The p redicted protein (zfZPC) has a calculated molecular mass of 58.4 kDa and co ntains a signal peptide (located in the N-terminal region) composed of 11 h ydrophobic amino acid residues followed by a signal peptide cleavage site. The zfZPC contains the ZP domain, a characteristic amino acid sequence shar ed by all ZP proteins of the mammalian zona pellucida and of both amphibian and bird egg envelope components. The zfZPC also exhibits certain unique f eatures including five N-terminal Q-rich tandem repeats presumably involved in the hardening of the chorion after the fertilization of the egg and a l ong C-terminal tail containing two potential sites of N-linked type glycosy lation, RT-PCR and in situ hybridization revealed a restricted pattern of t issue distribution: the gene encoding zfZPC is transcribed only in the grow ing oocyte of sexually mature female fish.