The mouse Ftzf1 gene required for gonadal and adrenal development maps to mouse chromosome 2

Steroidogenic factor-1 (SF-1, Ad4BP, NR5A1) and disorders of testis development

Steroidogenic factor-1 (SF-1) (Ad4BP, NR5A1) is a nuclear receptor that regulates many aspects of adrenal and reproductive development and function. Consequently, deletion of the gene (Nr5a1) encoding Sf-1 in XY mice results in impaired adrenal development, complete testicular dysgenesis with Mullerian structures, and female external genitalia. Initial efforts to identify NR5A1 changes in humans focused on 46,XY individuals with combined adrenogonadal failure and Mullerian structures. Although this combination of clinical features is rare, 2 such patients harboring NR5A1 mutations have been described within the past decade. More recently, however, it has emerged that heterozygous loss of function mutations in NR5A1 can be found relatively frequently in children and adults with 46,XY disorders of sex development (DSD) but with apparently normal adrenal function. The phenotypic spectrum associated with these changes ranges from complete testicular dysgenesis with Mullerian structures, through individuals with mild clitoromegaly or genital ambiguity, to severe penoscrotal hypospadias or even anorchia. Furthermore, a non-synonymous polymorphism in NR5A1 may be associated with micropenis or undescended testes within the population. Taken together, these reports suggest that variable loss of SF-1 function can be associated with a wide range of reproductive phenotypes in humans.

SF1 in the development of the adrenal gland and gonads

SF1 (steroidogenic factor-1; NR5A1) is an orphan nuclear receptor that is expressed in the adrenal gland, gonads, spleen, ventromedial hypothalamus and pituitary gonadotroph cells. Combined approaches of targeted mutagenesis in mice and examination of the effects of naturally occurring mutations in humans have clarified the role of SF1 in steroidogenesis and development. Targeted disruption of SF1 (FTZF1) in mice prevents gonadal and adrenal development and causes male-to-female sex reversal. A heterozygous loss-of-function human SF1 mutation (G35E) was described in a patient with adrenal failure and complete 46,XY sex reversal, indicating that haploinsufficiency of this transcription factor is sufficient to cause a severe clinical phenotype. In an infant with a similar clinical phenotype, a homozygous SF1 mutation (R92Q) was identified. In functional assays, this mutant SF1 protein exhibited partial loss of DNA binding and transcriptional activity when compared with the more severe G35E P-box mutant. These patients reveal the exquisite sensitivity of SF1-dependent developmental pathways to gene dosage and function in humans.

A polymorphic form of steroidogenic factor-1 is associated with adrenocorticotropin resistance in y1 mouse adrenocortical tumor cell mutants

ACTH resistance in mutant derivatives of the Y1 mouse adrenocortical tumor cell line results from a defect that affects the activity of steroidogenic factor-1 (SF1), thereby preventing the expression of the melanocortin-2 receptor. In this report, we show that the SF1 genes in ACTH-resistant mutants differ from the gene in ACTH-responsive Y1 cells by two base changes-one that changes an Ala to Ser at codon 172, and one in the third position of codon 3 that does not affect the protein sequence. Furthermore, several of the mutants contain multiple copies of this alternate SF1 gene (SF1(S172)) on acentric chromosome fragments. The SF1(S172) allele represents a polymorphism rather than a spontaneous mutation because the two SF1 alleles can be traced to the hybrid mouse strain (C57L/J x A/HeJ) from which the original adrenal tumor was derived. The SF1(A172) allele also is found in C57Bl/6J and C57Bl/10J mice, whereas the SF1(S172) allele also is found in C3H/HeJ and DBA/2J mice. The two forms of SF1 had only modest differences in activity suggesting that the SF1 polymorphism per se is not directly responsible for ACTH resistance. Our results indicate that the SF1(S172) allele is a marker of ACTH resistance in this family of adrenocortical tumor cells.

Phenotypic spectrum of mutations in DAX-1 and SF-1

SF-1 (steroidogenic factor-1) (NR5A1) and DAX-1 (dosage-sensitive sex-reversal, adrenal hypoplasia congenital, X chromosome) (NR0B1) are orphan nuclear receptors that are expressed in the adrenal gland, gonads, ventromedial hypothalamus (VMH), and pituitary gonadotrope cells. The function of these genes has been clarified by examining the consequences of naturally occurring mutations in humans, as well as targeted disruption of the genes in mice. Mutations in DAX1 cause adrenal hypoplasia congenita (AHC), an X-linked disorder characterized by adrenal insufficiency and failure to undergo puberty because of hypogonadotropic hypogonadism. Most DAX1 mutations introduce frameshifts and/or cause premature termination of the protein. Relatively few missense mutations have been described and all are located within the carboxy-terminal half of the protein. Transfection assays demonstrate that AHC-associated DAX1 mutations abrogate its ability to act as a transcriptional repressor of SF-1. Most boys affected with AHC present with adrenal insufficiency in early infancy, although a significant fraction present in later childhood or even as young adults. The degree of gonadotropin deficiency is also variable. With the exception of one mild missense DAX1 mutation, genotype-phenotype correlations have been elusive, suggesting an important role for modifier genes. Targeted mutagenesis of Dax1 (Ahch) in mice reveals an additional role in testis development and spermatogenesis. Similar abnormalities appear to be present in humans. Targeted mutagenesis of Sf1 (FtzF1) prevents gonadal and adrenal development, and causes male-to-female sex-reversal. A human XY individual with a heterozygous SF1 mutation presented with adrenal insufficiency and complete sex-reversal; this DNA-binding domain mutation prevents SF-1 stimulation of its target genes. In addition to their clinical relevance, studies of SF1 and DAX1 are proving useful for unraveling the genetic pathways that govern adrenal and gonadal development.