CIRCADIAN REGULATION OF GENE EXPRESSION IN THE ELECTRIC ORGAN OF THE GYMNOTIFORM FISH BRACHYHYPOPOMUS GAUDERIO

Abstract

Endogenous cellular circadian clocks have been shown to be major regulators of metabolic functions. The nocturnal gymnotiform fish Brachyhypopomus gauderio has emerged as a good candidate animal system to study the cellular and molecular mechanisms underlying the circadian regulation of energy metabolism. B. gauderio produce a weakly electric signal, referred to as an electric organ discharge (EOD), for habitat navigation and communication with conspecifics. The EOD displays sexual dimorphism, circadian regulation, and is highly energetically expensive. While both sexes of B. gauderio exhibit larger signals in the nighttime compared to the daytime, males exhibit a much larger signal increase in the nighttime. This enhanced nighttime EOD requires a large portion of a male’s energy budget to EOD production. In addition, the EOD circadian change is mediated at the cellular level by hormones, such as melanocortins and androgens, and their effects on electrogenic membrane channels and transporters, such as voltage-gated sodium channels and sodium-potassium ATPases. However, genes associated with the link between the circadian rhythm and energy regulation have yet to be fully characterized in the electric organ of B. gauderio. For my Honours thesis project, I have used direct RNA sequencing to characterize the expression of genes in the electric organ from male (n=8) and female (n=4) B. gauderio, sampled during daytime and nighttime. When comparing nighttime to daytime, I found 231 upregulated genes and 108 down regulated genes in the EO of male B. gauderio samples, and 32 upregulated genes and 36 downregulated genes in the EO of female B. gauderio. Using a false discovery rate (FDR) statistical approach, I was able to identify significant differentially expressed genes in males, but not in females, and to categorize these genes into molecular mechanisms and regulatory pathways that may support males’ EOD enhancement at night. Of note, the results of this study XIV showed upregulation of specific genes associated with the insulin-like growth factor 2 and ATPase pathway. This has given more evidence and insight into the role the insulin-like growth factor 2 and ATPase pathway may have on underlying the circadian regulation of the electric signal and its energetic cost in B. gauderio.