Effect of Point Mutation in the Growth Differentiation Factor ۹ Gene of Oocytes on the Sterility and Fertility of Awassi Sheep

Growth differentiation factor ۹ (GDF۹) plays a critical role in ovarian follicular development and ovulation rate. The present study aimed to investigate the correlation between the single-nucleotide polymorphism (SNP) of the GDF۹ gene and reproductive performance variables, such as fertility and sterility in Awassi sheep. Forty pairs of ovaries from a total of ۴۰ slaughtered Iraqi Awassi ewes were used in this study. Twenty of the ovaries were collected from sterile ewes and the other ۲۰ ovaries were taken from fertile ewes for genomic DNA extraction, polymerase chain reaction, and sequencing to detect GDF۹ gene polymorphism. Follicles and oocytes of all the ۴۰ ovaries were evaluated and compared with the results of genotyping. Furthermore, histopathological and microscopic evaluations were performed for ۴۰ ovarian tissues of the two groups. The sequence analysis revealed that exon I had three SNPs, including T(۱۱۴)C, G(۱۲۹)R, and G(۱۹۹)A. The first two SNPs were silent mutations and the last mutation was missense responsible for the substitution of glutamic acid with lysine at position ۶۷. The current study showed a significant increase (P≤۰.۰۱) in GG, AA, CC, GA, and GG genotypes at G(۱۲۹)R,  G(۱۹۹)A, T(۱۱۴)C, G(۱۲۹)R, and  G(۱۹۹)A loci, respectively. Moreover, the TT genotype in locus T(۱۱۴)C was recorded to significantly augment (P≤۰.۰۵) in the fertile ewes. Mutant GA genotype of the G(۱۲۹)R locus led to a significant (P≤۰.۰۵) increase in the percentage of follicles (۴-۸ mm) and oocytes number, compared to wild GG. On the other hand, a significant decrease was recorded in the mutant AA genotype in G(۱۹۹)A, compared to wild GG. Differences between CC and TT genotypes at T(۱۱۴)C locus were not significant. Histopathological examination revealed hypoplasia in the ovarian tissue of sterile ewes accompanied by fibrous connective tissue invasion and follicles degeneration. However, in the fertile ewes, the ovarian tissues were normal with the presence of numerous corpus albicans and degenerative corpus luteum. According to the findings of this study, the homozygote mutation in fertile ewes minimized the number of follicles and oocytes leading to sterility, while the heterozygote mutation was reported in the fertile Awassi ewes.

Keywords:

fertility , Heterozygote , Homozygote , Infertility