Search

Among vertebrate species, fishes are considered to be the most developmentally diverse taxa exhibiting remarkable gonadal plasticity with capacity of sex reversal. Sex determination in teleost fishes is governed via a complex regulatory network involving multiple genetic, environmental (temperature, population density, pH), social interaction/stress factors. Piscine germ-line originates as Primordial germ cells (PGC) from cleavage blastomeres/endoderm and gets specified by maternal inheritance of Vasa, Nanos, Tdrds, Dnd, Dazl etc and subsequently migrates to reach the embryonic gonadal primordium. Post-hatching, mitotically active germ cells (Gc) continue to proliferate via two distinct pathways-firstly, stem cell-like mode followed by meiosis-committed cystic division. In Japanese rice fish medaka, Oryzias latipes sex gets determined on the chromosomal basis, where XY becomes a male because of testicular Dmy transcription and XX develops as female owing to Gc restricted Foxl3 expression. Sex specific germ-line stem cell systems also have been found in adult O. latipes. Intriguingly in teleost fishes, the developmental fate of transplanted Gc do not depend on the sex of the donor rather solely relies upon the sex of the recipient. Furthermore, sexually mature piscine gonads remain developmentally plastic showing extensive responsiveness towards sex steroids. The critical regulation of gonadal differentiation is directed by female specific 17β-estradiol (E2) and bio-active male androgen 11-keto-testosretone (11-kT). Various transcription factors (TFs) e.g.- Dmrt1, DAX1, Ad4BP/SF-1, Foxl2 regulate the bio-conversion rate of testosterone (T) to either E2 or 11-kT. Similarly, multiple endocrine factors (EFs) e.g.- LH, FSH, E2, 11-kT and growth factors (GFs) e.g- AMH, GSDF, IGF-1/3, GDF-9/BMP-15 critically induce Gc differentiation to regulate the gametogenic output. In this article we have precisely discussed the endocrine regulation of Gc development during gonadal maturation of teleosts.

Schizothorax plagiostomus commonly known as snow-trout, is a popular game-food fish, found in the cold waters of the rivers, streams, tributaries and lakes of the Hindukush- Karakoram- Himalayan mountains/ foothills even at the elevation of 1180–3000 m above from the sea level and is considered to the be major source of animal protein. In recent past, there has been a severe decline in Schizothoracine population due to uncontrolled anthropogenic activities and climate change. Therefore, there is an urgent need for critical analysis of annual gonadal development in Schizothorax species. In this study, the seasonal variations of testicular architecture and development were examined in adult S. plagiostomus at Garhwal Himalaya, Uttarakhand, India. Testicular-somatic index were found to be ranged from 0.254 ± 0.06–7.104 ± 1.62 with maximal value recorded in September-October and minimal in April-May. Testicular histology revealed abundance of undifferentiated spermatogonia, meiotic spermatid and spermatozoa in pre-spawning and spawning capable phases respectively. The ultra-structure of spermatozoa showed 1.78 ± 0.27 µm long ovoid shaped head without any acrosome, 0.35 ± 0.05 µm long ellipsoidal mid-piece and 22.5 ± 0.65 µm long flagella. We further have evaluated the milt/semen volume, estimated the sperm density and motility in male brooders. Notably the spermatogenic capacity was found to be consistent in two breeding seasons i.e. spawning capable (September-October) and residual spawning (February-March) phases. In summary, this is the first comprehensive qualitative and quantitative report of the seasonal variations of the spermatogenic output in adult male S. plagiostomus. This data may provide valuable information for the conservation management and artificial breeding program of S. plagiostomus.

Germ cells (Gc) propagate the genetic information to subsequent generations. Diploid (2n) Gc get transformed to specialized haploid (n) gametes by mitotic and meiotic divisions in adult gonads. Retinoic acid (RA), an active derivative of vitamin A (retinol), plays a critical role in organ morphogenesis and regulates the meiotic onset in developing Gc. Unlike ovaries, fetal testes express an RA-degrading enzyme CYP26B1, and thereby, male Gc fail to enter into meiosis and instead get arrested at G0/G1 stage, termed as gonocytes/pro-spermatogonia by embryonic (E) 13.5 days. These gonocytes are transformed into spermatogonial stem/progenitor cells after birth (1–3 days of neonatal age). During post-natal testicular maturation, the differentiating spermatogonia enter into the meiotic prophase under the influence RA, independent of gonadotropic (both FSH and LH) support. The first pulse of RA ensures the transition of undifferentiated type A spermatogonia to differentiated A1 spermatogonia and upregulates STRA8 expression in Gc. Whereas, the second pulse of RA induces the meiotic prophase by augmenting MEIOSIN expression in differentiated spermatogonia B. This opinion article briefly reviews our current understanding on the RA-driven spermatogonial differentiation in murine testes.

Using unactivated alkylsulfinic acids as an alkyl radical source, a novel and highly practical visible-light-assisted synthetic methodology for the alkylation/annulation of a series of N-arylacrylamides into corresponding 3,3-dialkylindolin-2-ones has been developed. This approach does not require a photosensitizer or any metal reagents because the development of an electron donor–acceptor complex between alkylsulfinates and 2-isocyano-1,1′-biphenyl (catalytic electron acceptor) allows, under visible-light irradiation, the preparation of desired products in good yields. The mildness, gram-scale synthesizability, no need for the use of toxic organic solvents and a transition metal, as well as suitability for the synthesis of bioactive compounds (used as progesterone antagonists and anti-depressants) are a few noteworthy features of this procedure. Furthermore, alkylsulfinic acids are stable, safe, easy to handle, and readily available compared to other alkyl radical donors (like N-(acyloxy)phthalimides and Katritzky salts) reported in the literature. [ABSTRACT FROM AUTHOR]

2-Chloro-3-substituted quinoxalines (3) are significant precursors in the synthesis of 2,3-di-unsymmetrically substituted quinoxalines, including quinacillin, which has been shown to be effective against a number of transplantable diseases and cancer cells. Despite the fact that there are two ways to produce 2-chloro-3-substituted quinoxalines (3), both procedures are hampered by high temperatures, metal contamination, and toxic reagents. A visible-light-induced radical cascade cyclization of ortho-diisocyanoarenes (1) with alkyl(aryl)sulfinic acids (2) and trichloroisocyanuric acid has been developed. Also, a plausible reaction mechanism and synthetic uses of 2-chloro-3-substituted quinoxalines (3) towards a few 2,3-di-unsymmetrically-substituted quinoxalines have been described. This novel approach easily accesses 2-chloro-3-substituted quinoxalines (3) in good yields, without using elevated temperatures, or metal- or toxic reagents. [ABSTRACT FROM AUTHOR]

A novel and effective blue LED-induced methodology has been developed to synthesize a number of 6-alkyl(aryl)phenanthridines from isocyanobiaryls and alkyl(aryl)sulfinates in ethyl lactate under aerobic conditions. This protocol did not require a photoredox catalyst, and the reaction was sparked by the photochemical activity of an electron donor–acceptor complex formed by the interaction of isocyanobiaryls with alkyl(aryl)sulfinates. The environmental friendliness, mildness, gram-scale synthesizability, lack of toxic organic solvents/additives, and lack of a transition metal are only a few notable advantages of this methodology. [ABSTRACT FROM AUTHOR]