Ovarian Carbonyl Reductase-Like 20β-Hydroxysteroid Dehydrogenase Shows Distinct Surge in Messenger RNA Expression During Natural and Gonadotropin-Induced Meiotic Maturation in Nile Tilapia1

Abstract

Meiotic maturation in fish is accomplished by maturation-inducing hormones. 17alpha,20beta-Dihydroxy-4-pregnen-3-one (17alpha,20beta-DP) was identified as the maturation-inducing hormone of several teleosts, including Nile tilapia. A cDNA encoding 20beta-hydroxysteroid dehydrogenase (20beta-HSD), the enzyme that converts 17alpha-hydroxyprogesterone to 17alpha,20beta-DP, was cloned from the ovarian follicle of Nile tilapia. Genomic Southern analysis indicated that 20beta-HSD probably exists as a single copy in the genome. The Escherichia coli-expressed cDNA product oxidized both carbonyl and steroid compounds, including progestogens, in the presence of NADPH. Carbonyl reductase-like 20beta-HSD is broadly expressed in various tissues of tilapia, including ovary, testis, and gill. Northern blot and reverse transcription polymerase chain reaction analyses during the 14-day spawning cycle revealed that the expression of 20beta-HSD in ovarian follicles is low from Day 0 to Day 8 after spawning and is not detectable on Day 11. Distinct expression was evident at Day 14, the day of spawning. In males, 20beta-HSD expression was observed continually in mature testes but not in immature testes of 30-day-old fish. In vitro incubation of postvitellogenic immature follicles (corresponding to Day 11 after spawning) with hCG induced the expression of 20beta-HSD mRNA transcripts within 1-2 h, followed by the final meiotic maturation of oocytes. In tissues such as gill, muscle, brain, and pituitary, however, hCG treatment did not induce any changes in the levels of mRNA transcripts. Actinomycin D blockade of hCG-induced 20beta-HSD expression and final oocyte maturation demonstrated the involvement of transcriptional factors. The carbonyl reductase-like 20beta-HSD plays an important role in the meiotic maturation of tilapia gametes.

Effects of Dietary Arachidonic Acid on the Reproductive Physiology of Female Atlantic Cod (Gadus morhua L.).

“…The low transcript levels of 20bhsd during final maturation and spawning in cod is in apparent contrast to some previous studies, which showed increasing expression during final maturation and spawning in other teleost species such as ayu (Plecoglossus altivelis), tilapia and rainbow trout (Nakamura et al, 2005;Senthilkumaran et al, 2002Senthilkumaran et al, , 2004Tanaka et al, 2002). On the other hand, (Bobe et al, 2003(Bobe et al, , 2004 did not find any changes in 20bhsd transcript levels in rainbow trout ovarian follicles during maturation and suggested involvement of other factors such as other enzymes or growth factors, and/or substrate availability.…”

“…This is in agreement with results reported in other species such as rainbow trout, tilapia and ayu (Nakamura et al, 2005;Senthilkumaran et al, 2002;Tanaka et al, 2002), where highest levels of 20bhsd transcripts were found in postovulatory follicles. Pinillos et al (2002) and Antonopoulou et al (2011) found that MIS plasma concentrations peaked two months after spawning in the tench (Tinca tinca) but, unlike the situation in huchen and carp (Miura et al, 2007), it was not correlated to onset of first meiosis.…”

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

“…Since the isolation of a cDNA encoding CR/20β-HSD from pig (4), many studies have targeted CR/20β-HSD orthologs as being responsible for maturation-inducing hormone (MIH) synthesis (7,(28)(29)(30)(31)(32). Some studies demonstrated weak 20β-HSD activity of CR/20β-HSD towards 17OHP (7,30), whilst others did not check its activity (28,29,31,32).…”

“…Subsequently, partial amino acid sequences of the purified enzyme were determined, and a cDNA encoding the protein has been isolated and characterized (4). Using the pig 20β-HSD cDNA as a probe, an ortholog was also isolated from the ovarian cDNA library of rainbow trout (5), and homologs have been isolated in other teleost fish as well (6,7). These homologous genes have been categorized as monomeric carbonyl reductase genes, which encode enzymes that possess wide substrate specificity for carbonyl compounds and are known as carbonyl reductase-like 20β-HSD (CR/20β-HSD) (5,6).…”

Blocking of progestin action disrupts spermatogenesis in Nile tilapia (Oreochromis niloticus)

“…Tilapia is an economically important species for aquaculture and also an ideal model for studying fish gametogenesis because of the availability of monosex larvae and well-studied functions of DHP during gamete maturation (Senthilkumaran et al 2002, Zhou et al 2007). However, the role of DHP in spermatogenesis during sexual differentiation remains largely unknown.…”