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Sox family proteins are characterized by a unique DNA-binding domain, a HMG box which shows at least 50% sequence similarity with mouse Sry, the sex-determining factor. At present almost 30 Sox genes have been identified. Members of this family have been shown to be conserved during evolution and to play key roles during animal development. Some are involved in human diseases, including sex reversal. Here we report the isolation of a novel member of the Sox gene family, Sox30, which may constitute a distinct subgroup of this family. Using a bacterially expressed DNA-binding domain of Sox30, we show that it is able to specifically recognize the ACAAT motif. Furthermore, Sox30 is capable of activating transcription from a synthetic promoter containing the ACAAT motif. The specific expression of Sox30 in normal testes, but not in maturing germ cell-deficient testes, suggests the involvement of Sox30 in differentiation of male germ cells. Mapping analyses revealed that the Sox30 gene is located on human chromosome 5 (5q33) and on mouse chromosome 11.

Secretion of growth hormone (GH) exhibits marked sexual dimorphism in the rat. To examine the underlying mechanism that involves hypothalamic GH-releasing factor (GRF), we determined pituitary CRF receptor mRNA levels in male and female rats and compared their in vitroabilities to release GRF, an endogenous ligand for GRF receptor. Female rats expressed GRF receptor mRNA at a level of only 15% (P<0.001) of that of male rats. Female rats also showed a 33% lower (P<0.01) ability to release GRF than male rats. These results indicate that the GRF secretion and action system of female rats is characterized by the combined reduction in GRF receptor expression and GRF-releasing capacity compared with that of male rats. This could explain the in vivofinding that spontaneous, GRF-triggered GH pulses are of much lower amplitude in the female than in the male rat.