17β-HSD type 12-like is responsible for maturation-inducing hormone synthesis during oocyte maturation in masu salmon¹²

Abstract

Abbreviated title: 17β-HSD12-like responsible for DHP production Key terms: 17α,20β-dihydroxy-4-pregnen-3-one, 20β-hydroxysteroid dehydrogenase, 17β-hydroxysteroid dehydrogenase, Oocyte maturation, Granulosa, Masu salmon, Oncorhynchus masou AbstractThe maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (DHP) was first identified in the amago salmon. However, although carbonyl reductase-like 20β-hydroxysteroid dehydrogenase (CR/20β-HSD) was reported to convert 17α-hydroxyprogesterone (17OHP) to DHP in rainbow trout, we previously found that CR/20β-HSD mRNA was not up-regulated in stimulated granulosa cells from masu salmon, which suggested that DHP is synthesized by a different enzyme. Accordingly, the present study aimed to identify the specific 20β-hydroxysteroid dehydrogenase (20β-HSD) responsible for DHP production by granulosa cells during final oocyte maturation in masu salmon. RNA-sequencing was performed on granulosa layers that were isolated from ovarian follicles at one month before ovulation and incubated with or without forskolin, which was used to mimic luteinizing hormone, and ~12 million reads were obtained, which yielded 71,062 contigs of > 100 bp. tBlastx analysis identified one contig (#f103496) as similar to 17β-hydroxysteroid dehydrogenase type 12 (hsd17β12); however, because the fulllength #f103496 sequence was different from hsd17β12, it was termed to hsd17β12-like (hsd17β12l). We found that mammalian cells transfected with full-length hsd17β12l exhibited considerable 20β-HSD activity, as indicated by efficient conversion of exogenous 17OHP to DHP. In addition, we found that hsd17β12l mRNA levels were consistently low in follicles during vitellogenic growth; however, the levels increased significantly during final oocyte maturation. The levels of hsd17β12l mRNA were also considerably increased in granulosa layers in which 20β-HSD activity was induced by salmon pituitary extract. Therefore, we suggest that hsd17β12l, not CR/20β-HSD, is the 20β-HSD responsible for DHP production by granulosa cells in masu salmon during final oocyte maturation.

17β-Hydroxysteroid dehydrogenase type 12 is responsible for maturation-inducing steroid synthesis during oocyte maturation in Nile tilapia

“…CR/20bhsd mRNA expression levels in follicles showed no response to SPE or HCG at all follicle stages. This result was similar to those of a previous study in which two forms of CR/20β-HSD were identified in masu salmon and the mRNA levels of both CR/20β-HSD typeA and typeB in the forskolin-induced granulosa were not greater than the levels observed in the control group (Ijiri et al, 2017). However, another study of Nile tilapia reported that full-grown (post-vitellogenic) immature follicles incubated with HCG, with centrally located germinal vesicles, induced the short-term expression of CR/20bhsd mRNA within 1-2 h, suggesting that an increase in CR/20bhsd mRNA expression prior to oocyte maturation is responsible for 20β-HSD activity (Senthilkumaran et al, 2002).…”

“…In masu salmon, the expression of hsd17β12l mRNA was limited in testis and follicle layers at final maturation (Ijiri et al, 2017). In tilapia, hsd17b12 mRNA showed the same expression pattern.…”

“…In vitro studies of ovarian follicles from zebrafish incubated with HCG have shown no effect on CR/20bhsd induction (Wang and Ge, 2002). Similarly, in masu salmon studies with gonadotropin induction, CR/20β-HSD has not been linked to DHP production (Ijiri et al, 2017).…”

“…Recently, Ijiri et al 2017 identified and characterized 17β-HSD12-like as a key enzyme catalyzing the final steps in the synthesis of DHP in masu salmon and showed that it is involved in DHP production in the granulosa cell layer during oocyte maturation. An in vitro investigation has shown a close relationship between the induction of 20β-HSD activity and up-regulation of hsd17β12-like (hsd17β12l) mRNA by forskolin and chum salmon pituitary extract (SPE) at one or two months before ovulation.…”

Identification, Expression and Evolution of Short-Chain Dehydrogenases/Reductases in Nile Tilapia (Oreochromis niloticus)

“…It is well known that SDRs play important roles in steroids and retinoids metabolism [25]. Expression, substrate specificity, and functions of hsd17b, hsd3b, and hsd11b in sex steroids biosynthesis were extensively investigated in several teleosts [41][42][43][44]. In this study, hsd3b7, rdh10b-2, rdh12b, dhrs3, dhrs7b, dhrs9, sdr39u1, hpgd-b1, far1, spra, and decr2 were identified as ovary-enriched genes, while hsd3b1, hsd11b1-b2, hsd11b2, rdh14b, kdsr, and ak7-a were identified as testis-enriched genes.…”