Temperature-dependent sex determination in the American alligator: expression of SF1, WT1 and DAX1 during gonadogenesis

Sex determination in mammals and birds is chromosomal, while in many reptil es sex determination is temperature dependent. Morphological development of the gonads in these systems is conserved, suggesting that many of the gene s involved in gonad development are also conserved. The genes SF1,WT1 and D AX1 play various roles in the mammalian testis-determining pathway. SF1 and WT1 are thought to interact to cause male-specific gene expression during testis development, while DAX1 is believed to inhibit this male-specific ge ne expression. We have cloned SF1 and DAX1 from the American alligator, a s pecies with temperature-dependent sex determination (TSD). SF1, DAX1 and WT 1 are expressed in the urogenital system/gonad throughout the period of all igator gonadogenesis which is temperature sensitive. SF1 appears to be expr essed at a higher level in females than in males. This SF1 expression patte rn is concordant with the observed pattern during chicken gonadogenesis, bu t opposite to that observed during mouse gonadogenesis. Although the observ ed sexual dimorphism of gonadal SF1 expression in alligators and chickens i s opposite that observed in the mouse, it is probable that SF1 is involved in control of gonadal steroidogenesis in all these vertebrates. DAX1 and WT 1 are both expressed during stages 22-25 of both males and females. However , there appear to be no sex differences in the expression patterns of these genes. We conclude that DAX1, WT1 and SF1 may be involved in gonadal devel opment of the alligator. These genes may form part of a gonadal-development pathway which has been conserved through vertebrate evolution. (C) 2000 El sevier Science B.V. All rights reserved.