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Abstract
The inner perivitelline layer (IPVL), the avian equivalent of the mammalian zona pellucida, is an extracellular glycoprotein coat that surrounds the hens ovulated oocyte. In order for syngamy to occur, sperm must bind and subsequently penetrate through the IPVL. In the chicken, three different glycoprotein components of the IPVL (ZPC, ZPB1, ZPD) have been suggested as being the avian sperm receptor. In addition to these ZP proteins, three other ZP genes have been characterized in the chicken genome (ZPA, ZPB2, and ZPX). The disparity in research reports concerning the avian ZP proteins necessitates additional research concerning the expression and regulation of avian ZP proteins. The mRNA expression of all six ZP genes was tested between two genetic lines of turkey hens that differ in fertility. Hepatic ZPB1 mRNA expression was significantly greater in the high fertility line (E line) than in the lower fertility line (F line). In addition, due to the prevalence of sperm penetrations of the IPVL overlying the germinal disc (GD) of the oocyte, the mRNA expression for granulosa derived ZP genes was compared between GD and non germinal disc (NGD) granulosa cells. ZPC mRNA expression was significantly higher in the NGD region of F line hens; however, ZPB2 mRNA expression was significantly greater in the GD region of both lines. The mRNA expression of the ZPC and ZPD was analyzed in broiler breeder F1, F3 and small yellow (SY) follicle granulosa cells cultured with steroid hormones (estrogen and testosterone) and gonadotropins (LH and FSH). Expression of both ZPC and ZPD mRNA was induced in SY granulosa cell cultured with T, LH, and FSH. F3 granulosa cells cultured with E2 and T had increased ZPD mRNA expression while FSH stimulated both ZPC and ZPD mRNA expression in F3 granulosa cells. The results suggest that the lower rates of fertility for the F line versus the E line may be related to the lower expression of ZPB1, and lower expression of ZPC in the GD region. Key Words: Zona Pellucida Proteins, Inner Perivitelline Layer, Turkeys, Fertility, Germinal Disc, Granulosa, Genetic Lines, Broiler Breeder Hens