|Budget Amount *help
¥12,200,000 (Direct Cost : ¥12,200,000)
Fiscal Year 1999 : ¥3,800,000 (Direct Cost : ¥3,800,000)
Fiscal Year 1998 : ¥5,800,000 (Direct Cost : ¥5,800,000)
Fiscal Year 1997 : ¥2,600,000 (Direct Cost : ¥2,600,000)
The DAX-1 provides one of the rare known examples of mammalian transcriptional repressors whose the loss of function is associated with a congenital disorder, Adrenal hypoplasia congenita (AHC). However, the information about the structure-function of the DAX-1 or its function at the molecular level is so limited. Therefore, we performed first in this project the mutation analysis of the DAX-1 gene in the 20 suspected patients with X-linked AHC from 16 families. We identified three frameshift mutation (151 delAG, 935delC, 1376delTinsG), three nonsense mutations (Y91X. Y271X, Q395X), five missense mutations (V269D, L278R. W291C, L466R) and two deletion mutations. We showed that these missense mutations reduced their ability to silence StAR promotor activity, suggesting nonfunctional. All missense mutations reported are located only in the C-terminal presumptive ligand-binding domain. Thus, it was suggested that the C-terminal half of the DAX-1 protein may be important than the N-termina
l half for DAX-1 function. The 3-D structure of the ligand binding domain we constructed also supported these findings. Clinical analysis showed that there was no correlation between the age at presentation and the type of the mutation. Furthermore, we identified five adolescent and adult patients with hypogonadotropic hypogonadism. Nevertheless, they retained normal Leydig cell functions, but they had impaired Sertoli cell function. This suggests that DAX-1 plays some role in gonadotropin secretion and also spermatogenesis. We could demonstrate that the wild type DAX-1 suppresses the LH β promoter activity, but the mutant DAX-1 displayed the loss of function for gonadotropin secretion.
We also analyzed the mechanism of action of DAX-1. This project suggested also DAX-1 suppress the human StAR gene promoter function, that it can act in part through cis element binding SF-1, and associates with the coactivaor RIP140, which modulates DAX-1 action. However, these analysis indicated that the full picture of the wide phenotypic variability in the patients with AHC may not be explained solely by the loss of the repressor function of the DAX-1 itself. Less