Supplementary Material for: Characterization and Developmental Expression Profile of the Steroidogenic Acute Regulatory Protein (StAR) in the Gonad-Mesonephros Complex of Lithobates sylvaticus

<br>The steroidogenic acute regulatory (StAR) protein is responsible for the movement of cholesterol across mitochondrial membranes and is therefore a key factor in regulating the timing and rate of steroidogenesis. In this study, we characterized the coding region of the <i>star </i>gene in the ranid <i>Lithobates sylvaticus </i>and studied <i>star</i> mRNA levels in steroidogenic tissues during development and under natural conditions. Our results support previous research showing that the StAR sequence is well conserved. We determined that <i>star</i> is expressed in both the interrenal and gonadal tissues of adults and in the tadpole gonad-mesonephros complex (GMC). The mRNA levels of <i>star</i> in the GMC were found to increase during tadpole development, reaching a maximum between Gosner stages (Gs) 32 and 38. We observed a significant drop in <i>star</i> mRNA levels at the end of prometamorphosis (Gs40-41), just before the start of the metamorphic climax. Significant differences in <i>star</i> levels between females and males, with males presenting higher levels than females, were detected at Gs36-38. To our knowledge, this is the first study that reports transitory <i>star</i> sex differences in tadpoles' developing GMC. Our results suggest an involvement of StAR in anuran late male GMC formation and development that requires further investigation.