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The nucleotide sequence of chicken Mx cDNA was reported earlier using the White Leghorn breed in Germany, but it showed no enhanced resistance to viruses. In this study, the nucleotide sequences of chicken Mx cDNA were determined in many breeds. A total of 25 nucleotide substitutions, of which 14 were deduced to cause amino acid exchanges, were detected, suggesting that the chicken Mx gene is very polymorphic. Transfected cell clones expressing chicken Mx mRNA were established after the Mx cDNA was constructed with an expression vector and introduced into mouse 3T3 cells, and the Mx genes from some breeds were demonstrated to confer positive antiviral responses to influenza virus and vesicular stomatitis virus. On the basis of the comparison among the antiviral activities associated with many Mx variations, a specific amino acid substitution at position 631 (Ser to Asn) was considered to determine the antivirally positive or negative Mx gene. Thus, a single amino acid substitution influences the antiviral activity of Mx in domesticated chickens

The molecular mechanism by which sperm triggers Ca 2C oscillation, oocyte activation, and early embryonic development has not been clarified. Recently, oocyte activation has been shown to be induced by sperm-specific phospholipase Cz (PLCz). The ability of PLCz to induce oocyte activation is highly conserved across vertebrates. In the present study, porcine PLCz cDNA was identified and the nucleotide sequence was determined. The expression pattern of porcine PLCz mRNA during the period of postnatal testicular development was shown to be similar to that of mouse PLCz. PLCz mRNA expression in the pig and mouse was detected only in the testes when the elongated spermatids had differentiated, and was detected from day 96 after birth in the pig. Histological examination of porcine testis during the period of postnatal development revealed the presence of spermatozoa from day 110 after birth. These findings suggest that the synthesis of PLCz mRNA starts when spermiogenesis is initiated. Microinjection of porcine PLCz complementary RNA into porcine oocytes demonstrated that porcine PLCz has the ability to trigger repetitive Ca 2C transients in porcine oocytes similar to that observed during fertilization. It was also found that porcine PLCz cRNA has the potential to induce oocyte activation and initiate embryonic development up to the blastocyst stage.

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An attempt was made to determine whether amino acid variation at position 631 in the chicken Mx protein definitely influences antiviral specificity, using an artificial mutation technique by which a single amino acid was reciprocally substituted between Ser (AGT) and Asn (AAT) at position 631 of the negative and positive chicken Mx, respectively. Using permanently transfected 3T3 cell lines, the antiviral potential of chicken Mx against vesicular stomatitis virus infection was analysed. The results indicated that the phenotype of antiviral activity depends on the amino acid difference at position 631; that is, the genotype coding Asn at position 631 corresponds to the positive antiviral phenotype, and the genotype coding Ser corresponds to the negative phenotype. The present study has confirmed that the antiviral specificity of chicken Mx protein is determined by an amino acid substitution at the carboxy terminus.