197 MOLECULAR CLONING AND EXPRESSION OF THE CASHMERE GOAT IZUMO GENE

Abstract

During the fertilization process, complex events are involved in the fusion between the reacted spermatozoa and the mature oocyte. Fusion implies that many proteins are present on the cell membrane of the gametes. Recently, a new protein, Izumo, has been shown to play a role in the sperm–egg fusion. Izumo was identified through the generation of a monoclonal antibody that inhibits this fusion. This protein belongs to the immunoglobulin superfamily type I transmembrane protein. Izumo can be detected only after acrosome reaction at the spermatozoal surface. The cashmere goat Izumo gene was identified and cloned by 3′ and 5′ rapid amplification of cDNA ends-PCR. The expression of cashmere goat Izumo was examined by RT-PCR and Northern blotting. The full-length cDNA of cashmere goat Izumo contains 1536 bp and an open reading frame of 1035 bp, encoding a polypeptide of 344 amino acids with a calculated molecular mass of 38.76 kDa and a theoretical isoelectric point of 8.18. This predicted amino acid sequence showed 89.82% amino acid identity with the bovine Izumo. The deduced amino acid sequence contained 3 conserved domains of the signal peptide, immunoglobulin-like domain, and transmembrane region. Reverse transcription-PCR and Northern blotting analysis showed that cashmere goat Izumo transcripts were highly expressed in the testis, caput, corpus, cauda epididymis. Cashmere goat Izumo may play a role in the biological process of fertilization.