Histological and transcriptomic insights into temperature-induced ovarian degeneration and lipid metabolism in the Chinese mitten crab (Eriocheir sinensis)

In this study, three experimental groups were arranged, including a normal temperature control group (Control group), a variable temperature (VT) group, and a constant temperature (CT) group. Histology, transcriptomics, and molecular biological techniques were employed to investigate the effects of temperature on ovarian degeneration in Eriocheir sinensis during overwintering. Histological results showed that temperature is one of the factors inducing ovarian degeneration in E. sinensis , and rising temperature could trigger premature ovarian degeneration. Subsequent transcriptomic analysis revealed that the expression levels of heat shock proteins (Hsps) were upregulated in the ovaries of E. sinensis under temperature stimulation, and these genes were involved in the MAPK signaling pathway, estrogen signaling pathway, and other pathways. These results indicated that Hsp genes act as key genes in response to temperature changes. In addition, metabolic pathways including cholesterol metabolism, glycerophosphatidylcholine metabolism, and fatty acid biosynthesis were also affected during ovarian degeneration. The expression of the Fas gene was downregulated in the ovaries of E. sinensis in the CT group. Finally, RT qPCR results demonstrated that the expression level of the fatty acid synthase gene Fas was significantly increased in the hepatopancreas of the CT group, remarkably upregulated in the ovaries of the VT group, but notably downregulated in the CT group. The expression levels of the triacylglycerol lipase gene Atgl in both the CT and VT groups were significantly higher than those in the control group. The expression levels of CPT, CAT, and SOAT1 genes in the ovaries of E. sinensis were significantly elevated during ovarian degeneration. These findings suggested that during ovarian degeneration, the ovary preferentially undergoes β - oxidation in mitochondria mediated by CPT and CAT. At this stage, triglycerides are not hydrolyzed, whereas fatty acid synthesis is enhanced in the hepatopancreas, followed by transportation to and uptake by the ovary.