Expression and function of the chicken W chromosome gene MIER3 in embryonic gonads

Abstract Background The sex chromosomes of birds are designated Z and W. The male is homogamous (ZZ), and the female is heterogamous (ZW). The chicken W chromosome is a degenerate version of the Z chromosome and harbors only 28 protein-coding genes. We studied the expression pattern of the W chromosome gene MIER3 (showing differential expression during gonadogenesis) in chicken embryonic gonads and its potential role in gonadal development. Results The W copy of MIER3 (MIER3-W) showed a gonad-baised expression in chicken embryonic tissues which was different with its Z copy. The conbined expression of MIER3 mRNA and protein were correlated with the gonadal phenotype, being higher in female gonads than in male gonads or female-to-male sex reversed gonads. Chicken MIER3 protein was highly expressed in the nucleus, with relatively lower expression in the cytoplasm. Overexpression of MIER3-W in male gonad cells suggested its effcet on GnRH signaling pathway (potentially through EGR1 and αGSU), cell proliferation and cell apoptosis. However, at the in vivo level, MIER3 overexpression did not change the sex phenotype of chicken embryos. Conclusions MIER3 expression was associated with the gonadal phenotype. It affected multiple signaling pathways and inhibited cell apoptosis. MIER3 may promote female gonadal development by regulating EGR1 and αGSU genes; however, it does not determine the sex differentiation of gonads. These findings enrich our knowledge of chicken W chromosome genes and support a more systematic and in-depth understanding of sex determination and gonadal development in chickens.