Search

Present study demonstrates that conspecific vitellogenin1 (CFVg1) induces oocyte maturation in the catfish, Clarias batrachus. CFVg1 is able to develop fertilizable eggs in the Clarias batrachus. Therefore, different in vitro oocyte culture experiments were designed to see whether CFVg1 has efficacy of oocyte maturation and its pathway. In in vitro oocyte culture experiment, CFVg1 showed a dose- and time-dependent response and 64% maturation was obtained at the dose level of 10 µg/ml or more. CFVg1 induction of oocyte maturation was confirmed by co-incubating CFVg1 with CFVg1-antiserum (a-CFVg1), which inhibited the CFVg1-induced oocyte maturation. To answer issues lead to the understanding of the mechanism of vitellogenin (Vg) on oocyte maturation, trypsin digested CFVg1 and Indian major carp Cirhinus mrigala Vg HAI (Hydroxy appetite peak I) also showed significant level of maturation. Actinomycin-D and cycloheximide blocked the effect of CFVg1, indicating that CFVg1 acts through transcription and translation. Theophylline, the phosphodiesterase inhibitor, and cAMP also inhibited the stimulatory effect of CFVg1 on oocyte maturation, indicating indirectly that CFVg1-induced oocyte maturation by decreasing the intracellular cAMP possibly by activating the phosphodiesterase enzyme. Trilostane, the 3β-HSD-blocker, did not inhibit the CFVg1-induced oocyte maturation but wortmannin and Ly294002 two mechanistically different specific inhibitors of PI3 kinase blocked the oocyte maturation. The results thus indicate that oocyte maturation in catfish by Vg may be regulated by two pathways: (1) through decreasing the intraoocyte cAMP level by activating the cAMP-PKA pathway and (2) by cAMP-dependent PI3K/Akt pathway. Therefore, there might be role of vitellogenin itself in initiation of oocyte maturation., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

The biological activities of catfish LH-like (semi-purified: s200a and purified Qa) and FSH-like (semi-purified: s200b and purified: Qb) were compared in intact and hypophysectomized female catfish, Clarias batrachus, during preparatory and the pre-spawning periods on vitellogenesis and ovarian maintenance, as well as in vitro final maturation of oocytes, germinal vesicle breakdown (GVBD). During preparatory period, in intact catfish, semi-purified FSH-like induced complete vitellogenesis through the production of estradiol-17β (E2) and vitellogenin (Vg) accompanied by the formation of SIII yolky oocytes. On the other hand, semi-purified LH-like had induced the formation of only SII (characterized by the appearance of cortical alveoli in cytoplasm) oocytes, which indicates the initiation of vitellogenesis. In hypophysectomized female catfish, purified LH-like but not FSH-like induced the formation of SII oocytes in the ovaries. Treatment with semi-purified LH- and FSH-like at the dose level of 5 µg/fish/day for 7 days significantly maintained the yolky oocytes in gravid catfish after hypophysectomy with a significant reduction in plasma Vg, but not E2 levels, indicating some unknown GtH-induced factor doing the job. In in vitro oocytes culture, both LH- and FSH-like induced GVBD, but the response was significantly more with LH-like than FSH-like. All these findings revealed that both LH-like and FSH-like have overlapping physiological functions, but their responses differ depending on the physiological status of the catfish.

Two gonadotropins (GtH; Qa and Qb) were purified by gel filtration and ion exchange chromatography from the pituitaries of Indian walking catfish ( Clarias batrachus). The presence of GtH during purification was assessed by in vitro oocyte maturation and in vivo steroidogenic activity, and their identities were determined by elution profiles, molecular weight, biological activities and yield. The molecular weights of Qa and Qb were 37 and 42 kDa, respectively, and composed of distinct subunits (Qa: 20 and 14 kDa and Qb: 26 and 18 kDa). Polyclonal antibodies raised against Qa immunostained Qa, Qb and pituitary GtH cells. A competitive Qa-ELISA was developed whose sensitivity was 6.25 ng mL−1 (1.25 ng well−1) with intra- (3.5%) and inter- (12.4%) assay coefficients of variation. Displacement curves parallel to the standard were obtained with plasma and pituitary extracts of catfish, Qb and carp GtHII. The assay was validated by measuring the plasma Qa levels after LHRH treatment and in relation to ovarian growth in the female catfish during different reproductive phases. Based on the results, Qa and Qb corresponded to fish LH and FSH respectively. The findings will increase the knowledge of the mechanisms controlling fish reproduction and identification of sensitive phases in fish in captivity for hormonal manipulation. [ABSTRACT FROM AUTHOR]