Effect of the point mutation in growth differentiation factor 9 gene in awassi sheep oocytes on sterility and fertility

Abstract

Growth differentiation factor 9 (GDF9) is play a critical role in ovarian follicular development and ovulation rate. The present research was performed to investigate the correlation between single nucleotide polymorphism (SNP) of GDF9 gene and reproductive performance such as fertility, sterility and follicles condition in Awassi breed. Forty pairs of ovaries from total 40 slaughtered Iraqi Awassi ewes were used in this study. Ovaries (20 n) were picked up from sterile ewes and another 20 gathered from fertile ewes. Genomic DNA was extracted from each ovary of the two groups and PCR-sequencing was applied to detect GDF9 gene polymorphism. Follicles and oocytes evaluation of samples (40 n) were done in each ovary and then compared with the genotyping. Furthermore, the histological and microscopic evaluations were performed for 40 ovarian tissues of the two groups. The sequence analysis revealed that there exist three SNPs in exon I; T(114)C, G(129)R and G(199)A, the 1st two were silent mutation and the last mutation was missense responsible for a glutamic acid →lysine substitution at position 67. In sterile ewes, the current study appeared higher significant increased (P<0.01) in GG genotypes at G(129)R locus and AA at locus G(199)A and significant increased (P<0.05) in CC genotype in T(114)C locus. Likewise, GA in G(129)R locus, GG genotypes in locus G(199)A reported higher significant increment (P<0.01), TT genotype in locus T(114)C recorded significantly increased (P<0.05) in fertile ewes. The GA and GG genotypes were recorded significant increased (P<0.05) in percentage of follicles (4-8mm) and oocytes number for G(129)R and G(199)A locus as compared with wild GG and mutant AA respectively, while non-significant differences were recorded between CC and TT genotype at T(114)C locus. The histological examination revealed a hypoplasia in ovarian tissue of sterile ewes accompanied with fibrous connective tissue invasion with follicles degeneration, whilst in fertile ewes; the ovarian tissues was normal with a presence of numerous corpus albicans and degenerative corpus leutium. This study concluded that the homozygote mutation is reported to be in fertile and minimizing number of follicles and oocyte (sterility), whilst the heterozygote mutation shows strong association with fertile Awassi ewes.