Ovarian carbonyl reductase-like 20β-hydroxysteroid dehydrogenase shows distinct surge in messenger RNA expression during natural and gonadotropin-induced meiotic maturation in Nile tilapia

• Published in: Biology of reproduction 2002-10, Vol.67 (4), p.1080-1086
• Main Authors: SENTHILKUMARAN, Balasubramanian, SUDHAKUMARI, Cheni-Chery, CHANG, Xiao-Tian, KOBAYASHI, Tohru, OBA, Yuichi, GUAN, Guijun, YOSHIURA, Yasutoshi, YOSHIKUNI, Michiyasu, NAGAHAMA, Yoshitaka
• Format: Article
• Language: English
• Subjects: Animal aquaculture; Animal productions; Biological and medical sciences; Freshwater; Fundamental and applied biological sciences. Psychology; Oreochromis; Oreochromis niloticus; Pisciculture; Tilapia nilotica; Vertebrate aquaculture
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1043/0006-3363(2002)067(1080:OCRLHD)2.0.CO;2

Meiotic maturation in fish is accomplished by maturation-inducing hormones. 17 a,20 b-Dihydroxy-4-pregnen-3-one (17 a,20 b-DP) was identified as the maturation-inducing hormone of several teleosts, including Nile tilapia. A cDNA encoding 20 b-hydroxysteroid dehydrogenase (20 b-HSD), the enzyme that converts 17 a-hydroxyprogesterone to 17 a,20 b-DP, was cloned from the ovarian follicle of Nile tilapia. Genomic Southern analysis indicated that 20 b-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 20 b-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 20 b-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, 20 b-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 20 b-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 20 b-HSD expression and final oocyte maturation demonstrated the involvement of transcriptional factors. The carbonyl reductase-like 20 b-HSD plays an important role in the meiotic maturation of tilapia gametes.