Regulation of 17α-Hydroxyprogesterone Production during Induced Oocyte Maturation and Ovulation in Amur Sturgeon (Acipenser schrenckii)

In several teleosts, 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) has been identified as a maturation-inducing steroid. DHP is synthesized from 17α-hydroxyprogesterone (17OHP) by 17β-hydroxysteroid dehydrogenase type 12-like (hsd17b12L). Along with 3β-hydroxysteroid dehydrogenase/Δ5-4 isomerase (3β-HSD), 17α-hydroxylase and C17-20 lyase are associated with 17OHP production. This study aimed to determine the roles of Amur sturgeon hsd3b, P450c17-I (cyp17a1), and P450c17-II (cyp17a2) in 17OHP production and to examine their enzyme activity and mRNA expression pattern during oocyte maturation. In the sturgeons used in this study, hsd3b encoded 3β-HSD, cyp17a1 catalyzed 17α-hydroxylase production with C17-20 lyase activity, and cyp17a2 processed 17α-hydroxylase activity alone. In the ovarian follicles of individuals that underwent induced ovulation, hsd3b mRNA levels increased rapidly, cyp17a1 expression was downregulated, and cyp17a2 expression was upregulated during oocyte maturation. Finally, an in vitro study revealed that salmon pituitary extract (SPE) stimulation rapidly induced hsd3b expression, whereas cyp17a1 expression was downregulated. In vitro, cyp17a2 expression did not rapidly increase with SPE stimulation. This rapid upregulation of hsd3b during oocyte maturation was first observed in teleosts. It was suggested that hsd17b12L expression is upregulated after 17OHP production, which is regulated by hsd3b, cyp17a1, and cyp17a2, resulting in DHP production.

Full-Length Gonad Transcriptome Analysis of Amur Sturgeon Dmrt Family Genes: Identification, Characterization and Expression Patterns During Gonadal Differentiation

The regulatory mechanisms that govern sex differentiation in sturgeon are still poorly understood. The doublesex and Mab-3-related transcription factor (Dmrt) gene family is known for its extensive roles in sex determination and differentiation across vertebrates. This study aimed to identify new members of sturgeon Dmrt family genes and core actors in the gonadal differentiation of Amur sturgeon. A full-length gonad transcriptome database was exploited to identify Dmrt gene orthologs. Analyses of phylogenetic relationships and selection pressure were performed, and tissue expression profiles and spatiotemporal expression patterns in gonads were then analyzed using real-time PCR. In total, five Dmrt family genes were identified from the full-length gonad transcriptome, including Dmrt2, DmrtA1, DmrtA2, DmrtB1a and DmrtB1b. Phylogenetic analysis showed that these genes were clustered into clades corresponding to the doublesex/Mav-3 (DM) genes of vertebrates. Furthermore, the analysis of evolutionary selective pressure indicated that DmrtB1a and DmrtB1b were subject to positive selection, suggesting the existence of adaptive evolution in sturgeon. The extensive tissues expression profiling of each Dmrt family gene revealed typical characteristics. Remarkably, according to a spatiotemporal expression pattern analysis, DmrtA1 and DmrtA2 were predominantly distributed in undifferentiated gonads (UGs) and developing ovaries, whereas DmrtB1b showed the lowest expression in UGs. In later stages, DmrtB1b expression continuously increased in testes and was significantly higher in testes than in ovaries at 24 months after hatching (M) and 36M, which strongly suggests that DmrtB1b is a core regulatory factor involved in sexual differentiation in sturgeon. This study provides a genetic resource of full-length Dmrt family genes and increases the understanding of Dmrt functions in sex differentiation in sturgeon.

Growing a triple hybrid of russian, siberian and amur sturgeons in a warm-water fish farm

Biological and production indices are presented for spawning females of triple hybrid between russian sturgeon, siberian sturgeon and amur sturgeon (RS × SS) × AS and other commercial forms of sturgeon grown in cages of the warm-water fish farm in Luchegorsk, Far East of Russia. In conditions of warm-water pools, survival rate of the triple hybrid larvae and juveniles was higher than that of amur sturgeon and russian-siberian hybrid sturgeon. Weight of the triple hybrid specimens at the age of 3 and 4 years was 1.58 kg and 2.36 kg, respectively, that was higher than that of the russian-siberian hybrid sturgeon and close to the values for amur sturgeon. Fish harvest reached 94 kg/m2 of cage, or 134 kg/m2 of cage in sum with the realized fish. Up to 93 % of females matured after using of hormonal stimulation. The first female of the triple hybrid sturgeon matured at the age of 9 years, with its body weight of 13.1 kg. Other females became matured in different age, up to 16 years, but ¾ of them were matured at the age of 10–12 years. The maximum registered weight of the triple hybrid female was 29 kg (age 14 years). Inter-spawning intervals for 97 % of females were 1–2 years. Average annual yield of hard roe obtained from one female at the age of 9–16 years was 2.28 kg, average weight of one egg was 17.6 mg, average fecundity was 132 . 103 eggs/female or 7.4 . 103 eggs/kg, average oosomatic index was 12.8 %. These values of production indices for the triple hybrid females are mainly intermediate between the indices of initial species. In 3–4 spawning seasons, the yield of 5.25 kg of hard roe, on average, was harvested from one female of the triple hybrid, or 30 % of its body weight. The yield from the most productive females was 10.8–11.0 kg of roe, or 55–73 % of their body weight. These values are lower than the yeild from amur sturgeon but similar to the yield value for russian-siberian hybrid sturgeon. Caviar manufactured from the roe of triple hybrid sturgeon is distinguished by high quality. Its females are technologically advanced for the eggs harvesting and have a good survival, about 98 % during long-term exploitation. So, the triple hybrid of russian, siberian and amur sturgeon can be recommended for commercial cultivation in warm-water sturgeon farms with intensive harvesting.