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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.

Schizothorax plagiostomus is found in the cold-water of Hindukush-Karakoram-Himalayan mountains/foothills and parts of Central Asia. The local cold-water fishery of Schizothoracinae supports the rural economy of this region. Despite of its wide range of presence and potential economic value, Schizothorax is a highly neglected ichthyo-fauna with disputed taxonomical status. In this study the sequence data of mitochondrial Cytochrome c oxidase subunit I (CO-I ) and Cytochrome b (Cyt b) gene have been employed to explain the phylogenetic relationship(s) between the S. plagiostomus from different riverine system and the phylogenetic relationship between seven species of Schizothorax keeping Schizothorax plagiostomus as a reference organism. Our data revealed the genetic proximity shared between S. niger, S. curvifrons , S. richardsonii, S. progastus , S. esocinus, S. labiatus and S. plagiostomus & S. esocinus.