Is regulation of aromatase expression in reptiles the key to understanding temperature-dependent sex determination?

A brief review of our current understanding (or lack of understanding) of the molecular basis of temperature-dependent sex determination (TSD) in reptiles is presented. Current theories are discussed: yolk steroids as sex determinants, the brain as the driver for TSD and the enzyme aromatase and estrogen production as the possible determinants of sex. There is little evidence to support the first two theories, but enough evidence to keep the third theory in play. As yet, however, we have no molecular understanding of how a two-degree difference in temperature during the temperature-sensitive phase of egg incubation can initiate the molecular cascade that determines whether the indifferent gonad develops as an ovary or a testis.