Browsing by Author "Robert P. Millar"

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Correction to: Role of Neurokinin B in gametogenesis and steroidogenesis of freshwater catfish, Clarias batrachus (Cell and Tissue Research, (2023), 393, 2, (377-391), 10.1007/s00441-023-03788-0)
(Springer Science and Business Media Deutschland GmbH, 2023) Ankur Singh; Bechan Lal; Pankaj Kumar; Ishwar S. Parhar; Robert P. Millar
The authors regret that Fig. 7 is a repetition of Fig. 6 as presented in the original article. The original figure for Fig. 7 is shown below. The legend and description for the figure (Fig. 7) remain the same but with some minor change. (Figure presented.) Western blots analysis of StAR, 3β-HSD, 17β-HSD (a) and pERK1/2, ERK1/2, pAkt & Akt proteins (b) in the testicular explants of Clarias batrachus incubated with 5 nM and 50 nM of MRK-08 for 24 h in vitro. The expression is presented as an integrated relative density value (IRDV) as an arbitrary unit. All the values are expressed as Mean ± SEM (n = 3). Means with the same superscript do not differ from each other, while means with different superscripts are different from each other statistically at p < 0.05 (Duncan’s multiple range test). Superscripts *, ** and *** are used for StAR, while superscripts # & ### are used for 3β-HSD and superscripts, and for 17β-HSD, respectively (Fig. 7a). Superscripts *, ** and *** are used for p44 and superscripts #, ## & ### for p42 while superscripts and for pAkt (Fig. 7b) The original article has been corrected. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Gametogenic and steroidogenic action of kisspeptin-10 in the Asian catfish, Clarias batrachus: Putative underlying mechanistic cascade
(Elsevier Inc., 2021) Ankur Singh; Bechan Lal; Jyoti Parkash; Robert P. Millar
Unlike mammals, two kisspeptins genes encoding, kiss1 and kiss2 are detected in fishes with highly varied and contradictory difference in their reproductive activities. The present study was undertaken to examine the direct action of kisspeptin-10 and its role in gonadal activities in the gonadally quiescent Asian catfish using native mammalian kisspeptin decapeptide (KP-10) involving in vivo and in vitro approaches. The in vivo KP-10 treatment caused precocious onset of gametogenesis and its rapid progression, as was evident from the appearance of advanced stages of ovarian follicles in ovary, and advanced germ cells (spermatocytes/ spermatids) in the testis of the treated Clarias batrachus in comparison to the control gonads. It also elevated the steroid levels in gonads of the catfish in vivo and in vitro conditions. Simultaneously, it increased the expressions of key steroidogenic enzymes like 3β-HSD, 17β-HSD, and StAR protein, responsible for transfer of cholesterol from outer to inner membrane of the mitochondria of steroidogenic cells. Concurrently, it augmented the activities of 3β-HSD and 17β-HSD in the ovarian explants. The expressions of MAPK component (pERK1/2 and ERK1/2) were also up-regulated by KP-10 in gonadal explants. Thus, the data suggest that kisspeptin-10 stimulates gametogenesis by enhancing gonadal steroid production. The study also describes the putative mechanistic cascade of steroidogenic actions of kisspeptin-10 in the catfish so much so in teleost fish. The study also suggests that, kisspeptin may act locally to regulate gonadal activities in an autocrine/paracine manner, independent of known extra-gonadal factors in the catfish. © 2021 Elsevier Inc.
Nitric oxide mediated kisspeptin regulation of steroidogenesis and gametogenesis in the catfish, Clarias batrachus
(Springer Science and Business Media Deutschland GmbH, 2024) Ankur Singh; Bechan Lal; Pankaj Kumar; Ishwar S. Parhar; Robert P. Millar
Nitric oxide (NO) is a gaseous molecule that regulates various reproductive functions. It is a well-recognized regulator of GnRH-FSH/LH-sex steroid secretion in vertebrates including fish. Kisspeptin is a recently discovered neuropeptide which also regulates GnRH secretion. Nitrergic and kisspeptin neurons are reported in close physical contact in the mammalian brain suggesting their interactive role in the release of GnRH. The existence of kisspeptin and NOS is also demonstrated in vertebrate gonads, but information on their reciprocal relation in gonads, if any, is obscure. Therefore, attempts were made to evaluate the functional reciprocal relation between nitric oxide and kisspeptin in the catfish gonads, if any, by administering the nitric oxide synthase (NOS) inhibitor, L-NAME {N(G)-nitro-l-arginine methyl ester}, which reduces NO production, and kisspeptin agonist (KP-10) and assessing their impacts on the expressions of kisspeptin1, different NOS isoforms, NO and steroid production in the gonadal tissue. The results revealed that L-NAME suppressed the expression of kiss1 in gonads of the catfish establishing the role of NO in kisspeptin expression. However, KP-10 increased the expression of all the isoforms of NOSs (iNOS, eNOS, nNOS) and concurrently NO and steroids in the ovary and testis. In vitro studies also indicate that kisspeptin stimulates the production of NO and estradiol and testosterone levels in the gonadal explants and medium. Thus, in vivo results clearly suggest a reciprocal interaction between kisspeptin and NO to regulate the gonadal activity of the catfish. The in vitro findings further substantiate our contention regarding the interactive role of kisspeptin and NO in gonadal steroidogenesis. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Role of Neurokinin B in gametogenesis and steroidogenesis of freshwater catfish, Clarias batrachus
(Springer Science and Business Media Deutschland GmbH, 2023) Ankur Singh; Bechan Lal; Pankaj Kumar; Ishwar S. Parhar; Robert P. Millar
Neurokinin B (NKB), a recently discovered neuropeptide, plays a crucial role in regulating the kiss-GnRH neurons in vertebrate's brain. NKB is also characterized in gonadal tissues; however, its role in gonads is poorly understood. Therefore, in the present study, the effects of NKB on gonadal steroidogenesis and gametogenesis through in vivo and in vitro approaches using NKB antagonist MRK-08 were evaluated. The results suggest that the NKB antagonist decreases the development of advanced ovarian follicles and germ cells in the testis. In addition, MRK-08 further reduces the production of 17β-estradiol in the ovary and testosterone in the testis under both in vivo and in vitro conditions in a dose-dependent manner. Furthermore, the in vitro MRK-08 treatment of gonadal explants attenuated the expression of steroidogenic marker proteins, i.e., StAR, 3β-HSD, and 17β-HSD dose-dependently. Moreover, the MAP kinase proteins, pERK1/2 & ERK1/2 and pAkt & Akt were also downregulated by MRK-08. Thus, the study suggests that NKB downregulates steroidogenesis by modulating the expressions of steroidogenic marker proteins involving ERK1/2 & pERK1/2 and Akt/pAkt signalling pathways. NKB also appears to regulate gametogenesis by regulating gonadal steroidogenesis in the catfish. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Seasonal expression and distribution of kisspeptin1 (kiss1) in the ovary and testis of freshwater catfish, Clarias batrachus: A putative role in steroidogenesis
(Elsevier GmbH, 2021) Ankur Singh; Bechan Lal; Ishwar S. Parhar; Robert P. Millar
The central role of kisspeptin (kiss) in mammalian reproduction is well established; however, its intra-gonadal role is poorly addressed. Moreover, studies investigating intra-gonadal role of kiss in fish reproduction are scanty, contradictory and inconclusive. The expression of kiss1 mRNA has been detected in the fish brain, and functionally attributed to the regulation of reproduction, feeding and behavior. The kiss1 mRNA has also been demonstrated in tissues other than the brain in some studies, but its cellular distribution and role at the tissue level have not been adequately addressed in fish. Therefore, an attempt was made in the present study to localize kiss1 in gonadal cells of the freshwater catfish, Clarias batrachus. This study reports the presence of kiss1 in the theca cells and granulosa cells of the ovarian oocytes and interstitial cells in the testis of the catfish. The role of kiss1 in the ovary and testis of the catfish was also investigated using kiss1 receptor (kiss1r) antagonist (p234). The p234 treatment decreased the production of 17β-estradiol in ovary and testosterone in the testis by lowering the activities of 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase under both, in vivo as well as in vitro conditions. The p234 treatment also arrested the progression of oogenesis, as evident from the low number of advancing/advanced oocytes in the treated ovary in comparison to the control ovary. It also reduced the area and perimeter of the seminiferous tubules in the treated catfish testis. Thus, our findings suggest that kiss is involved in the regulation of gonadal steroidogenesis, independent of known endocrine/ autocrine/ paracine regulators, and thereby it accelerates gametogenic processes in the freshwater catfish. © 2021 Elsevier GmbH