Transcriptional study of appetite regulating genes in the brain of zebrafish (Danio rerio) with impaired leptin signalling

Abstract

The hormone leptin is a key regulator of body weight, food intake and metabolism. In mammals, leptin acts as an anorexigen and inhibits food intake centrally by affecting the appetite centres in the hypothalamus. In teleost fish, the regulatory connections between leptin and other appetite-regulating genes are largely unknown. In the present study, we used a zebrafish mutant with a loss of function leptin receptor to investigate brain expression patterns of 12 orexigenic and 24 anorexigenic genes under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-hours refeeding). Expression patterns were compared to wild-type zebrafish, in order to identify leptin-dependent differentially expressed genes under different feeding conditions. We provide evidence that the transcription of certain orexigenic and anorexigenic genes is influenced by leptin signalling in the zebrafish brain. We found that the expression of orexigenic genes was not affected by impaired leptin signalling under normal feeding conditions; however, several orexigenic genes showed increased transcription during fasting and refeeding, including agrp, apln, galr1a and cnr1. This suggests an inhibitory effect of leptin signal on the transcription of these orexigenic genes during short-term fasting and refeeding in functional zebrafish. Most pronounced effects were observed in the group of anorexigenic genes, where the impairment of leptin signalling resulted in reduced gene expression in several genes, including cart family, crhb, gnrh2, mc4r, pomc and spx, in the control group. This suggests a stimulatory effect of leptin signal on the transcription of these anorexigenic genes under normal feeding condition. In addition, we found multiple gain and loss in expression correlations between the appetite-regulating genes, in zebrafish with impaired leptin signal, suggesting the presence of gene regulatory networks downstream of leptin signal in zebrafish brain. The results provide the first evidence for the effects of leptin signal on the transcription of various appetite-regulating genes in zebrafish brain, under different feeding conditions. Altogether, these transcriptional changes suggest an anorexigenic role for leptin signal, which is likely to be mediated through distinct set of appetite-regulating genes under different feeding conditions.

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

“…In mammals, leptin has been shown to be an upstream transcriptional stimulator of several anorexigenic genes in the brain, such as Cart, Crh, Mc4r, POMC (Schwartz et al 1996;Thornton et al 1997;Ghamari-Langroudi et al 2011;Lee et al 2013), suggesting that leptin mediates its effects on feeding behaviour through induction of these genes in the brain. However, in fish, similar positive regulatory connections have only recently been reported between leptin signal and transcription of these anorexigenic genes in zebrafish (Ahi et al 2019a). In general, little is known about leptin-dependent regulatory mechanisms in fish and previous attempts to reveal the complexity of leptin mediated transcriptional regulation of biological processes have mainly addressed its other physiological roles (e.g.…”

“…In our previous study, we found no phenotypic difference under normal feeding condition, using a different loss of function zebrafish lepr mutant (Ahi et al 2019a). However, based on our recent observations, the same zebrafish lepr mutant showed significant increase in length and weight under overfeeding (unpublished data).…”

“…Experimental set-up and sampling of tissues Detailed description of the experimental set-up can be found in Ahi et al (2019a). Briefly, siblings wild-type and lepr mutant zebrafish fish were randomly selected at the beginning of the experiment from different stock tanks of fish and put in a 3-l tank together for each genotype and for each feeding category: fish fed normally (control group); fish fasted for a week; fish fasted for a week and sampled 2 h after refeeding; and fish fasted for a week and sampled 6 h after refeeding (Supplementary data 1).…”

Gnrh2 maintains reproduction in fasting zebrafish through dynamic neuronal projection changes and regulation of gonadotropin synthesis, oogenesis, and reproductive behaviors

“…We first examined Gnrh2 and Gnrh3 neuronal pituitary patterns in fed, 7-day fasted, and 14-day fasted conditions. In zebrafish, one week of fasting induces changes in both brain and gut appetite-regulating genes 35 , 36 and two weeks of fasting induces liver protein and other enzyme responses 37 and previously shown to induce plasticity of Gnrh2 33 . Therefore, we chose two weeks fasting as our end point in this analysis, of which there was no mortality in any of our experiments.…”

Alarm Test: A Novel Chemical-Free Behavioural Assessment Tool for Zebrafish

“…While ZFs can be used for modelling liver cancer [11], diabetes [12,13], cardiovascular disorders [14,15] and other metabolic disorders [16,17], the major contribution of this model is projected in neurodegenerative sciences. This is due to the extensive similarity of its brain structure with that of the humans [18,19]. The incidences of neurodegenerative diseases in the growing population have increased worldwide, and it is expected that its prevalence will rise in the next few years.…”