Steroid 5-reductases are functional during early frog development and are regulated via DNA methylation

• Steroid 5-reductases are functional during early anuran development.
• Gene regulation of srd5 is based on a positive feedback loop mechanism.
• DNA methylation may be involved in regulating srd5α1 and srd5α3.
• Steroid metabolites have crucial roles in multiple tissues during early development.
• srd5α1, srd5α2, srd5α3, and srd5β show unique expression pattern during embryogenesis.

In adulthood, steroid 5-reductases (Srd5) are known to synthesize androgens from testosterone and to play important physiological roles, in particular during reproduction. However, less is known about their regulation and function during early development. To deepen the understanding on Srd5 in amphibian species, we investigated the mechanistic regulation of four important genes (srd5α1, srd5α2, srd5α3, and srd5β) via 1) chemical enzymatic inhibition and 2) specific DNA methylation imprinting. Indeed, this is the first study to suggest that Srd5 are functional during the critical early developmental period of vertebrates. Moreover, exposure to Srd5 inhibitors showed that the regulation of srd5 in early development are self-regulated, with decreasing mRNA levels after exposure, consistent to the regulation mechanism in juvenile frog liver. Furthermore, data highlighted a potential novel mechanism of regulation for srd5α1 and srd5α3, i.e., through DNA methylation. This opens up important questions regarding the role of a transgenerational effect in the regulation of these crucial genes through maternal transfer. This study also profiled the expression of srd5 throughout early development for the first time in any vertebrate and suggested that steroid metabolites produced by Srd5 have crucial roles in development of the central nervous, sensory, cardiac, respiratory, and detoxifying systems aside from reproduction in early anuran development.