Gene Expression and Antioxidant Characteristics of Rainbow Trout (Oncorhynchus mykiss) Eggs Used for Meiotic Gynogenesis

Gynogenesis is a reproductive mode where offspring inherit exclusively maternal chromosomes. Gynogenetic development in fish may be induced intentionally by activating eggs with the UV-irradiated, inactive spermatozoa. In the meiotic variant of gynogenesis, the resultant haploid gynogenetic zygote is then exposed to a physical shock to inhibit the release of the 2nd polar body and to reconstitute the diploid state of the embryo. Here, meiotic gynogenesis was induced in the rainbow trout eggs from different clutches to find any differences in terms of gene expression and antioxidant enzyme activity between eggs with high and low ability for gynogenetic development. The survival rates of the gynogenotes after hatching from the eggs originating from five females varied from 16.6 ± 4.3% to 53.8 ± 9.8%. Biochemical and molecular examination revealed that eggs with higher developmental potential for meiotic gynogenesis exhibited significantly greater glutathione peroxidase (GPx) activity than eggs with lower efficiency of gynogenesis. Moreover, eggs exhibiting the highest ability for gynogenetic development showed increased transcription of the keratin 8 gene and decreased abundance of keratin 18 and tubulin β mRNA transcripts. Since keratins protect oocytes from physical stress after ovulation, the high abundance of keratin 8 in the rainbow trout eggs may increase their resilience to the physical shock applied for the zygote diploidization during gynogenesis. On the other hand, a low level of tubulin-building microtubules may increase the efficiency of high hydrostatic pressure (HHP) shock used for diploidization of the gynogenetic zygotes.