Winter hibernation and UCHL1-p34cdc2 association in toad oocyte maturation competence

Multi-omics analysis reveals that natural hibernation is crucial for oocyte maturation in the female Chinese alligator

BACKGROUND

Hibernation in an appropriate environment not only is important for the survival of hibernators in winter, but also is crucial for breeding in the following season for many hibernating species. However, the genetic and epigenetic mechanism underlying this process remain unclear. In the current study, we performed an integrative multi-omics analysis of gonads collected from Chinese alligators that overwintered in wild cave and artificial warmroom to explore transcriptomic and epigenomic alternations in these organs.

RESULTS

The data revealed that in the breeding season, female alligators were more strongly affected in terms of gene expression than males by non-hibernation because of overwintering in a warm room, especially for genes related to oocyte maturation, and this effect commenced in winter with the downregulation of STAR, which is the rate limiting factor of steroid biosynthesis. Further, miRNAs were found to play essential roles in this negative effect of overwintering in the warm room on hibernation. The upregulated miRNAs likely were responsible for the suppression of oocyte maturation in the breeding season. Finally, DNA methylome changes, especially hypomethylation, were found to play an important role in the alterations in ovarian function-related gene expression induced by non-hibernation.

CONCLUSIONS

Our study revealed the crucial role of hibernation quality for oocyte maturation in the Chinese alligator and the underlying genetic and epigenetic mechanisms, and highlights the importance of habitat, and especially, the overwintering site, in the conservation of not only the Chinese alligator, but also other endangered hibernators.

Gene UCHL1 expresses specifically in mouse uterine decidual cells in response to estrogen

UCHL1 is expressed specifically in the brain and gonads of almost all studied model organisms including Drosophila, zebrafish, amphibians, and mammals, suggesting a high degree of evolutionary conservation in its structure and function. Although UCHL1 has been involved in spermatogenesis in mice, its specific expression in mammal placenta remains elusive. Our previous work has revealed that UCHL1 is highly expressed in oocytes, and has been involved in mouse ovarian follicular development. Here, we further examined UCHL1 expression change in endometria during early natural pregnancy, with different stages of the estrous cycle and pseudopregnancy as control. The UCHL1 gene deletion model showed that UCHL1 protein is associated with endometrial development, and its deletion leads to infertility. Notably, we demonstrate evidence showing the distinct expression pattern of UCHL1: weak expression over the uterine endometria, strong expression in decidualized stromal cells at the implantation site with a peak at pregnancy D6, and a shift with primary decidualization to secondary decidualized zones. Using the delayed implantation, the delayed implantation activation, and the artificial decidualization models, we have demonstrated that strong expression of UCHL1 occurred in response to decidualization and estrogen stimulation. These observations suggest that during the early proliferation and differentiation of mouse uterine decidua, UCHL1 expression is up-regulated, and formed an unique intracellular distribution mode. Therefore, we proposed that UCHL1 is involved in decidualization, and possibly in response to estrogen regulation.