A cross-talk between leptin and 17β-estradiol in vitellogenin synthesis in rainbow trout Oncorhynchus mykiss liver

Seasonality, sex-specificity and transcriptional regulation of hepatic leptin system in spotted snakehead Channa punctata

The present study deals with sex-specific reproductive phase-dependent variation and sex steroids-induced transcriptional regulation of hepatic lep and lepr in nutritionally valuable spotted snakehead, Channa punctata. The data on seasonality reveals sex-specific variation in pattern of lep transcription where a high level was recorded during resting and postspawning quiescent phases in female while during resting and spawning phases in male. Unlike lep, lepr exhibited similar expression pattern along the reproductive phases in both the sexes. As compared to female, a three-fold higher expression of lep was detected in male during reproductively active phase only. However, no sexual dimorphism was evidenced in lepr either during active or quiescent phase. To explore the implication of sex steroids in regulation of leptin system, we correlated levels of plasma testosterone (T) and 17β-estradiol (E₂) with leptin system in males as well as females. Further, criss-cross in vivo and in vitro experiments with dihydrotestosterone (DHT) and E₂ were conducted in male and female spotted snakehead. The leptin system was downregulated after DHT administration in both the sexes. However, with E₂, a marked decrease was evidenced in male only. The sex-wise variable response of leptin system to sex steroids was validated by in vitro experiments wherein liver fragments from male and female fish were incubated individually with both the sex steroids. In conclusion, sex steroids modulate hepatic leptin system differentially depending on sex and reproductive state of spotted snakehead.

Transcriptional study reveals a potential leptin-dependent gene regulatory network in zebrafish brain

The signal mediated by leptin hormone and its receptor is a major regulator of body weight, food intake and metabolism. In mammals and many teleost fish species, leptin has an anorexigenic role and inhibits food intake by influencing the appetite centres in the hypothalamus. However, the regulatory connections between leptin and downstream genes mediating its appetite-regulating effects are still not fully explored in teleost fish. In this study, we used a loss of function leptin receptor zebrafish mutant and real-time quantitative PCR to assess brain expression patterns of several previously identified anorexigenic genes downstream of leptin signal under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-h refeeding). These downstream factors include members of cart genes, crhb and gnrh2, as well as selected genes co-expressed with them based on a zebrafish co-expression database. Here, we found a potential gene expression network (GRN) comprising the abovementioned genes by a stepwise approach of identifying co-expression modules and predicting their upstream regulators. Among the transcription factors (TFs) predicted as potential upstream regulators of this GRN, we found expression pattern of sp3a to be correlated with transcriptional changes of the downstream gene network. Interestingly, the expression and transcriptional activity of Sp3 orthologous gene in mammals have already been implicated to be under the influence of leptin signal. These findings suggest a potentially conserved regulatory connection between leptin and sp3a, which is predicted to act as a transcriptional driver of a downstream gene network in the zebrafish brain.