Temperature-dependent sex determination is mediated by pSTAT3 repression of .

In many reptiles, including the red-eared slider turtle (), sex is determined by ambient temperature during embryogenesis. We previously showed that the epigenetic regulator is elevated at the male-producing temperature and essential to activate the male pathway. In this work, we established a causal link between temperature and transcriptional regulation of We show that signal transducer and activator of transcription 3 (STAT3) is phosphorylated at the warmer, female-producing temperature, binds the locus, and represses transcription, blocking the male pathway. Influx of Ca, a mediator of STAT3 phosphorylation, is elevated at the female temperature and acts as a temperature-sensitive regulator of STAT3 activation.