Mark Leshin

Hereditary Male Pseudohermaphroditism Associated with an Unstable Form of 5α-Reductase

The properties of 5alpha-reductase have been compared in genital skin fibroblasts cultured from five patients from three families (Los Angeles, Dallas, and Dominican Republic) in which hereditary male pseudohermaphroditism has been established to result from deficient conversion of testosterone to dihydrotestosterone. Despite the fact that 5alpha-reductase was immeasurable in a homogenate of epididymis removed from one of the Los Angeles patients, 5alpha-reductase activity was normal in intact fibroblasts and fibroblast extracts from both patients from the Los Angeles family. Although the apparent K(m) for testosterone was also near normal, the apparent K(m) for NADPH in these mutants is elevated some 40-fold above normal. Furthermore, the enzyme is not protected against denaturation at 45 degrees C by concentrations of NADPH that stabilize normal 5alpha-reductase, and in intact fibroblasts from these patients (but not from controls), enzyme activity decreases promptly when protein synthesis is inhibited. We conclude that the mutation in this family results in an unstable enzyme. In contrast 5alpha-reductase activity in fibroblast extracts from a patient from the Dominican Republic family is similar to that previously described in two members of the Dallas family, namely total enzyme activity is low at the optimal pH for the normal reaction, and the apparent K(m) for testosterone is some 20-fold higher than that of the controls. We conclude that the mutations in the Dallas and Dominican Republic families are similar and result in low activity of the enzyme as the result of a decreased affinity for testosterone.Thus, two distinct types of mutations can produce male pseudohermaphroditism due to deficient dihydrotestosterone formation.

The Role of Gonadal Steroids in Sexual Differentiation

Publisher Summary The embryos of both sexes develop in an identical fashion for the first two months of gestation. Only thereafter does anatomical and physiological development diverge to result in the formation of the male and female phenotypes. Gonadal steroids play an important role in sexual differentiation. This chapter discusses this particular role. Male development is induced in the embryo only in the presence of specific hormonal signals arising from the fetal testis. According to the Jost formulation, sexual differentiation is a sequential, ordered, and relatively simple process. Chromosomal sex, established at the time of conception, directs the development of either ovaries or testes. If testes develop, their hormonal secretions elicit the development of the male secondary sex characteristics, collectively known as the male phenotype. If an ovary develops—or if no gonad is present—anatomical development is female in character. Thus, it is the action of the gonads as endocrine organs that is responsible for the development of the sexual phenotypes. The chapter describes current concepts of the processes by which the fetal gonads acquire the capacity to function as endocrine organs and of the mechanisms by which the endocrine secretions of the fetal testis modulate male development. It also gives an overview of the anatomical events involved in the formation of the sexual phenotypes and the factors that mediate this development.

Role of Gonadal Hormones in Development of the Sexual Phenotypes

SummaryMale and female embryos develop in an identical fashion during the initial portion of gestation. If the indifferent gonad differentiates into an ovary (or if no gonad is present), a female phenotype is formed. Male phenotypic differentiation, however, requires the presence of an endocrinologically active testis. Two secretion of the fetal testis, Müllerian inhibiting substance and testosterone, are responsible for male development. Studies of single gene mutations that interfere with androgen action indicate that testosterone itself is responsible for virilization of the Wolffian duct system into the epididymis, vas deferens, and seminal vesicle, whereas the testosterone metabolite dihydrotestosterone induces development of the prostate and male external genitalia. Thus, impairment of dihydrotestosterone formation results in a characteristic phenotype consisting of predominantly female external genitalia but normally virilized Wolffian ducts. The molecular mechanisms by which testosterone and dihydrotestosterone act during fetal development appear to involve the same high affinity receptor, a protein that transports both testosterone and dihydrotestosterone to the nucleus of target cells. When this receptor is either absent, deficient, or structurally abnormal, the actions of both testosterone and dihydrotestosterone are impaired, and the resulting developmental anomalies involve both internal and external genital structures.

Inhibition of steroid 5α-reductase from human skin fibroblasts by 17β-N, N-diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one

Abstract The capacity of 17 β - N , N -diethylcarbamoyl-4-methyl-4-aza-5 α -androstan-3-one (DMAA) to inhibit competitively steroid 5α-reductase has been confirmed in human foreskin fibroblasts. The inhibitor works equally well in homogenates and in intact cells, is rapidly reversible, does not influence the amount of the enzyme, is equally effective in inhibiting the 5α-reduction of testosterone, 4-androstene-3,17-dione, 20α-hydroxy-4-pregnen-3-one and cortisol, and appears to be weakly bound to serum protein. The inhibitor is particularly effective (apparent K i of approximately 3 nM) at the optimal pH of the enzyme (pH 5.5) and has no effect in the alkaline range (pH 9.0). DMAA appears to be a steroid that will be useful in the investigation of 5α-reduction of steroid hormones in intact animals and in embryos.

ENDOCRINE CONTROL OF SEXUAL DIFFERENTIATION IN THE HUMAN

Publisher Summary This chapter discusses the endocrine control of sexual differentiation in the human. It describes sexual differentiation as an ordered and sequential process. Chromosomal sex, established during fertilization, directs the development of gonadal sex. Hormonal secretions from the fetal testes then transform the phenotypically indifferent embryonic urogenital tract into that of the male. Despite the difference in chromosomal constitution, the gonads and the urogenital tracts of male and female embryos develop initially in an identical manner. The first evidence of sexual dimorphism in the human embryo is the appearance of the spermatogenic cords in the fetal testes between week 6 and week 7 of gestation. The factors involved in the differentiation of the ovaries and testes are not fully understood, but the characterization of the male-specific histocompatibility antigen (HY antigen) has provided a working model to explain the mechanisms by which the Y chromosome directs testicular development. During the indifferent stage of sexual development, the urogenital tract of the embyro consists of two components: (1) two duct systems (wolffian and mullerian), derived from the mesonephros, and (2) the urogenital sinus and genital tubercle. The development of the internal urogenital tract of the male involves regression and ultimate disappearance of the mullerian ducts as well as the growth and differentiation of the wolffian ducts into the epididymides, vasa deferentia, and seminal vesicles. In females, the mullerian ducts persist to form the fallopian tubes, the uterus, and the upper portion of the vagina, and the wolffian ducts degenerate. Thus, the internal genital tracts develop from different anlagen in the two sexes.

Characterization of the increased estrogen synthesis in skin fibroblasts from the Sebright bantam.

We have utilized the Sebright bantam chicken as a model system to explore the regulation of estrogen formation in peripheral tissues. As the result of a gene mutation, Sebright males develop a female feathering pattern associated with an increase in estrogen synthesis in skin and in fibroblasts cultured from skin. To provide insight into the mechanisms by which estrogen synthesis is increased we examined several parameters of the aromatase reaction in homogenates from control ovaries, Sebright ovaries and fibroblasts grown from Sebright skin: the pH optima; the apparent Kms for testosterone, 19-nortestosterone, androstenedione, 16-hydroxyandrostenedione, and NADPH; the apparent Kis for 4-hydroxyandrostenedione, aminoglutethimide, dehydroepiandrosterone, and 19-hydroxytestosterone; and the inactivation of the reaction by heating. No qualitative differences were identified in the enzyme from Sebright and control birds.

Genetic control of extraglandular aromatase activity in the chicken

Feminization of feathers in the Sebright cock is the result of increase in the activity of skin aromatase. This increased estrogen synthesis is the consequence of an autosomal dominant mutation that causes an increase in the specific androgen-binding cytochrome P450 oxidase involved in the reaction. Since this oxidase appears to be kinetically indistinguishable from the activity in control ovary we believe that the mutation causes an increased steady-state level of normal enzyme. The mechanism by which the mutation acts is unknown, but its presence implies that in normal birds an allele of the mutation limits the activity of the enzyme in all tissues other than ovary.