Steroidogenic gene expression following d-aspartate treatment in frog testis

Previous studies have provided evidence that d-Asp plays a role in steroid-mediated reproductive biology in amphibians, reptiles, birds and mammals. To examine the molecular involvement of d-Asp on steroidogenic pathway regulation, we analysed the expression of StAR, P450 aromatase and 5αRed2 mRNAs in Pelophylax esculentus testis, either in relation to the reproductive cycle or d-Asp treatment. Basal StAR mRNA levels, as well as d-Asp and testosterone concentrations, were higher in reproductive than in post-reproductive frogs. d-Asp treatment increased StAR mRNA expression and immunolocalisation in both the reproductive and post-reproductive periods. In control testis, aromatase mRNA levels were higher in the post-reproductive period, but following d-Asp administration, they increased only in the reproductive period. The level of 5αRed2 mRNA was higher in reproductive frogs than in post-reproductive frogs, and it increased after d-Asp treatment only in the post-reproductive phase. Our results suggest that, in P. esculentus testis, d-Asp increases StAR mRNA in both periods, and P450 aromatase and 5αRed2 mRNAs at different points during the reproductive cycle.

► In Pelophylax esculentus testis, StAR, P450 aromatase and 5α-reductase mRNA levels change during annual cycle. ► d-Asp treatment increases StAR mRNA levels and immunolocalization in both reproductive and postreproductive periods. ► In reproductive phase, aromatase expression increases with consequent 17β-estradiol synthesis following d-Asp administration. ► In post-reproductive period, both testosterone concentrations and 5α-reductase mRNA levels increase in d-Asp injected frogs. ► d-Asp affects reproductive processes, activating gene expression of key enzymes involved in steroidogenic pathway.