Expression of chicken zygote arrest 1 (Zar1) and Zar1-like genes during sexual maturation and embryogenesis

Maternal mRNAs, which are expressed in oocytes, play an important role in the success of early embryo development, as they allow the first cleavages to occur. Zygote arrest 1 (Zar1) is an oocyte-specific maternal-effect gene that functions at the oocyte-to-embryo transition in many vertebrate species including human, pig, cattle, sheep, mouse, rat, frog and zebrafish. Recently, through in silico studies, a gene structurally related to Zar1, called Zar1-like has been identified in many vertebrates, including the chicken. The objectives of this study were to investigate the expression of the chicken Zar1 and Zar1-like genes in chicken tissues and embryos and to determine whether sexual maturation affects their mRNA abundance. RNA was extracted from various organs of chickens aged from one month up to two years old and from chicken embryos until day ten of embryonic development. Expression analysis of the genes was performed using RT-PCR and real-time PCR. RT-PCR analysis revealed that both genes were preferentially expressed in chicken oocytes, ovary and testes and in embryos during embryonic development. Quantitative real-time PCR analysis revealed a significant up regulation of Zar1 in the mature ovary, and also a significant up regulation of Zar1 and Zar1-like genes in the testes of sexually mature roosters, suggesting a key role of these genes in the chicken fertility. In contrast, expression of Zar1-like was not affected by age in the chicken ovary. Our results indicate that the chicken Zar1 and Zar1-like transcripts are co-expressed in high levels in the chicken gonads. In addition their expression beyond the stage of embryonic genome activation suggests an embryonic and not only a maternal origin of these transcripts.