| The objective of this study was to identify essential factors of the oocyte surface which altered sperm-egg binding in subfertile hens among growth-selected lines of chicken. The central biological basis of this project not only addressed the identification of factors involved in sperm-egg binding, but specifically targeted those factors associated with genes influencing growth by utilizing populations generated from a double divergent selection program. This program consisted of meat-type, or broiler, chickens that were divergently selected for growth rates at two early periods of development. As a result, four lines were produced exhibiting different developmental patterns of growth, which had associated with them unique reproductive characteristics. Birds selected for increased rate of growth between hatch and 42 days of age (42H) became sexually mature earlier and at a larger body weight than other lines. However, birds selected for slow growth during this period (42L) became sexually mature later and at a lower body weight than other lines. The weight and age at sexual maturity did not appear to be affected by selection for growth between hatch and fourteen days of age (14H, 14L), suggesting that factors involved in initiating ovulation were associated with growth factors during this critical period between 14 and 42 days of age. Birds selected for slow growth at fourteen days of age (14L) exhibited severely reduced fertility while other lines appeared unaffected. An in vitro sperm binding assay using heat-solubilized egg membrane proteins (HS-EM) from individual females of each line also revealed that eggs from 14L birds were considerably reduced in their ability to bind sperm compared to the other selected lines.;Gel electrophoresis of heat-solubilized egg membrane extractions revealed the presence of a 22 kD protein in over 60% of individuals from the 14L line compared to less than 5% in subsequent lines. Tryptic digestion of the isolated protein revealed several internal peptides with over 60% homology to zona pellucida protein type-3 (ZP3) from bovine, human and mouse. These sequences were nearly identical to a cDNA-derived ZP3-like protein from chicken reported in the Genbank database (Accession No. D89097). However, amino-terminus sequencing revealed a 23 amino acid sequence with 64% identity to mouse zona pellucida protein type-1 (ZP1). In addition, antibodies raised against the 22 kD peptide in rabbits appear to be associated with similar antigenic properties as antibodies made against several mammalian ZP epitopes. |
