Rhythmicity in testicular melatonin and its correlation with the dynamics of spermatogenic cells in an annual reproductive cycle of Clarias batrachus under natural photo-thermal conditions.

Melatonin, the pineal hormone, is synthesized and secreted rhythmically in accordance with various environmental cues especially photo-thermal conditions. The reproductive physiology of seasonal breeders is synchronized with the surroundings by melatonin as a neuroendocrine mediator to acts as an important factor in fish reproduction. However, the data on the participation of melatonin in male reproduction and the putative interaction with the process of spermatogenesis in fish is scarce till date. So, major objectives of the current study are to determine for the first time, the relationship, if any, between seasonal levels of melatonin and testicular development and maturation of the germ cells, and also the involvements of specific meteorological parameters in spermatogenesis under natural photo-thermal conditions. We measured the concentration of circulatory and testicular melatonin; value of gonadosomatic index (GSI), relative percentages of different developing spermatogenic cells, area and perimeter (size and shape) of seminiferous lobules along with the level/duration of rainfall, water temperature and day length in six reproductive phases throughout an annual cycle in adult male catfish (Clarias batrachus). Intra-testicular and serum melatonin concentration showed a similar seasonal pattern with a peak during "functional maturity" phase and trough during "slow spermatogenesis" phase. Correlation as well as regression analyses also supported this positive relationship. Interestingly, intra-testicular melatonin also showed a significant positive correlation with GSI and relative percentage as well as lobular size of mature stages (spermatid and spermatozoa) of germ cells in an annual cycle. Furthermore, meteorological factors exhibited as critical cues to regulate the dynamics (in %) of spermatogenic cells and the level of testicular melatonin throughout the annual gonadal cycle. Our results corroborated by principal component (PC) analysis and showed very clearly that active "functional maturity" state is characterized by GSI, testicular melatonin, relative abundance and lobular size of mature spermatogenic stages as key internal oscillators; and studied environmental variables as the external clues for the regulation of spawning process. Collectively, the present data revealed that there is a relationship between melatonin levels and testicular growth and development of germ cells in Clarias batrachus under natural photo-thermal conditions.

In silico study to unravel molecular networking of melatonin in the regulation of gametogenesis.

Melatonin, a pineal hormone, has potential role on steroidogenesis, growth and maturation of sperm and ovum during gametogenesis. The possible use of this indolamine as an antioxidant in the production of good quality gametes opens up a new area of current research. Nowadays, a large number of reproductive dysfunctions like infertility and failure in fertilization due to gametic malformations are major concern worldwide. So, understanding molecular mechanisms including interacting genes and their action is a prerequisite to the therapeutic approach against these issues. The aim of present bioinformatic study is the detection of molecular network concerning therapeutic potential of melatonin in gametogenesis. It includes target genes identification, gene ontology, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, network analysis, prediction of signalling pathways and molecular docking. We obtained common top 52 targets of melatonin in the process of gametogenesis. They are involved in biological processes related to the development of gonads and primary sexual characteristics and sex differentiation. We took top 10 pathways out of total 190 enriched pathways for further analysis. Subsequently, principal component analysis also revealed that among top ten hub targets (TP53, CASP3, MAPK1, JUN, ESR1, CDK1, CDK2, TNF, GNRH1 and CDKN1A), only TP53, JUN and ESR1were significantly interacted with melatonin on the basis of squared cosine value. So, present in silico investigation provides considerable information on the interactive network between therapeutic targets of melatonin along with the involvement of intracellular signalling cascade regulating biological processes associated with the gametogenesis. This novel approach may be pertinent in improving modern research on reproductive dysfunctions associated abnormalities.