Changes in Ovulation-Related Gene Expression during Induced Ovulation in the Amur Sturgeon (Acipenser schrenckii) Ovarian Follicles

Comparative proteomic analysis of the ovarian fluid and eggs of Siberian sturgeon

BACKGROUND

Sturgeon species are living fossils that exhibit unique reproductive characteristics, and elucidation of the molecular processes governing the formation and quality of sturgeon eggs is crucial. However, comprehensive data on the protein composition of sturgeon ovarian fluid (OF) and eggs and their functional significance are lacking. To address this knowledge gap, the aim of the present study was to conduct a comprehensive comparative proteomic analysis of Siberian sturgeon OF and eggs using liquid chromatography-mass spectrometry (LC-MS/MS).

RESULTS

A total of 617 proteins were identified in OF, and 565 proteins were identified in eggs. A total of 772 proteins showed differential abundance. Among the differentially abundant proteins, 365 were more abundant in OFs, while 407 were more abundant in eggs. We identified 339 proteins unique to OFs and 287 proteins specific to eggs, and further investigated the top 10 most abundant proteins in each. The functional annotation of the OF proteins highlighted their predominant association with immune system processes, including the complement and coagulation cascade, neutrophil and leukocyte-mediated immunity, cholesterol metabolism, and regulation of the actin cytoskeleton. Analysis of egg proteins revealed enrichment in metabolic pathways, such as oxidative phosphorylation and fatty acid metabolism, and protein ubiquitination and translation. OF-specific proteins included extracellular matrix and secretory vesicles, and eggs were enriched in proteins localized to mitochondria and ribosome components.

CONCLUSIONS

This study presents the first comprehensive characterization of the protein composition of sturgeon OF and eggs and elucidates their distinct functional roles. These findings advance our understanding of sturgeon reproduction, OF-egg signaling and the origin of OF proteins. The mass spectrometry proteomics data have been deposited in the ProteomeXchange Consortium with the dataset identifier PXD044168 to ensure accessibility for further research.

Identification of maturation-inducing steroid in sturgeons via comprehensive analyses of steroids produced during oocyte maturation

Although 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) and 17α, 20β, 21-trihydroxy-4-pregnen-3-one (20β-S) have been identified as maturation-inducing steroids (MIS) in several teleosts, to date, no MISs have been identified in sturgeons. As it remains possible that an unidentified steroid is an MIS in sturgeons, this study aimed to identify a sturgeon MIS via comprehensive analyses and maturation-inducing (MI) assay of C21 steroids. In vivo and in vitro comprehensive analyses of C21 steroids revealed that serum DHP concentrations were rapidly elevated in the oocyte maturation phase and the DHP production level was notably high among C21 steroids. MI assay indicated that the MI activity of DHP, 17α-hydroxyprogesterone (17OHP), a precursor of DHP, 17α, 20α-dihydroxy-4-pregnen-3-one (αDHP), and 20β-S was high among C21 steroids, but the MI activity of these steroids were similar. In the C21 steroids produced in ovarian follicles during oocyte maturation, 17OHP, αDHP, and unidentified compounds had a low production level, and 20β-S was suggested to be metabolized from DHP after oocyte maturation. Against this background, this study concluded that DHP is a steroid that possesses strong MI activity and is highly produced during oocyte maturation. Although this study could not identify an MIS in sturgeons by fractionation of plasma and subsequent bio assay, it was suggested that DHP is a major MIS in sturgeons.