Mechanisms of gonadal differentiation

Sexual Differentiation and Sex Differences in Neural Development

Sex determination occurs at the moment of conception, as a result of XX or XY chromosome pairing. From that point, the body undergoes the process of sexual differentiation, inducing the development of physical characteristics that are easily distinguishable between the sexes and are often reflected in one's physical appearance and gender identity. Although less apparent, the brain also undergoes sexual differentiation. Sex differences in the brain are organized during a critical period of neural development and have an instrumental role in determining the physiology and behavior of an individual throughout the lifespan. Understanding the extent of sex differences in neurodevelopment also influences our understanding of the potential risk for a number of neurodevelopmental, neurological, and mental health disorders that exhibit strong sex biases. Advances made in our understanding of sexually dimorphic brain nuclei, sex differences in neural cell communication, and sex differences in the communication between the brain and peripheral organs are all research fields that have provided valuable information related to the physiological and behavioral outcomes of sex differences in brain development. More recently, investigations into the impact of epigenetic mechanisms on sexual differentiation of the brain have indicated that changes in gene expression, via epigenetic modifications, also contribute to sexual differentiation of the developing brain. Still, there are a number of important questions and ideas that have arisen from our current understanding of sex differences in neurodevelopmental processes that necessitate more time and attention in this field.

Behavioral gender differences in the neonatal period according to the Brazelton scale

The aim of the present study was to analyze gender differences in neonatal behavior. A sample of 188 healthy full-term newborns (88 boys and 100 girls) was assessed. The behavioral evaluations were performed using the Brazelton Neonatal Behavioral Assessment Scale (NBAS), when the infants were between 48 and 80 hours old. Girls had higher scores than boys in 4 out of the 34 behavioral items of the NBAS. These are the following: Orientation Animate Auditory (t=2.486; P=0.014), Alertness (t=2.546; P=0.012), Quality of Alertness (t=3.091; P=0.002), and State Regulation (t=2,343; P=0.020). Boys had higher scores in the Irritability item (t=-2.186; P=0.030). We have analyzed also the possible effects of the medication during delivery because mothers of boys were more likely to have used this medication but no differences have been found among the mentioned items. These results appear to confirm that similarities between boys and girls are much more the norm than differences related to gender, but even though they are quite subtle, differences do exist in the way newborn infants react and behave in the neonatal period.

Early aspects of sex differentiation in the gonads of chick embryos

In chick embryos whose sex had been previously identified by cytokaryologic methods, a light-microscope study of the number and dimensions of the germ cells (GCs) has been made from 2 to 7 days of incubation. Early differences between the sexes have been found. In females the GCs were larger and increased in number earlier than in males. This suggests an earlier differentiation of GCs in females. On the other hand, ultrastructural observations on GCs at 70 h incubation (colonization stage of the genital ridges) have revealed that male and female GCs differ from each other mainly in the amount of rough and smooth endoplasmic reticulum, mitochondria, glycogen particles and lipid droplets. This suggests early morpho-functional differences between male and female GCs.

Sexual differentiation of neuroendocrine systems and behavior

Differentiation of the reproductive system occurs in stages, with early development of the gonads and later differentiation of the brain. The physiological mechanisms that are involved in the sequence of events during sexual differentiation have not been clearly understood. However, recent technological advances have made understanding these mechanisms much more accessible. Many of these techniques have been used to elucidate the nature of steroid-induced effects on target tissues, hormonal and neuroendocrine interactions, and the molecular basis of these processes. This review will focus on the sequence of events and mechanisms associated with sexual differentiation of endocrine, morphological, and behavioral components of reproduction in the chicken and Japanese quail.

Isolation and properties of androgenic gland hormone from the terrestrial isopod, Armadillidium vulgare

The androgenic gland hormone (AGH) was purified from the male reproductive organs, including the androgenic glands, of Armadillidium vulgare by pH adjustment, ammonium sulfate precipitation, gel filtration, ion-exchange chromatography, and three kinds of high-performance liquid chromatography (HPLC). AGH consisted of two molecular forms, AGH I and AGH II. They were judged as homogeneous by HPLC, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and isoelectrofocusing, though their N-terminal residues were not detected. They seem to be monomeric proteins consisting of 157 and 166 amino acid residues, having molecular weights of 17,000 +/- 800 and 18,300 +/- 1000, and having isoelectric points of about 4.5 and 4.3, respectively. The activities of AGH I and AGH II were almost the same and their respective specific activities were 560 and 430 times that of the crude extract.

Endocrine disorders in children

The childhood endocrine disorders in which surgical intervention is a common or indispensable part of management are succinctly reviewed. Pathophysiology and rational approaches to diagnosis are emphasized.

Alteration of behavioral sex differentiation by exposure to estrogenic compounds during a critical neonatal period: effects of zearalenone, methoxychlor, and estradiol in hamsters

The present study was designed to determine if neonatal exposure to the estrogenic mycotoxin zearalenone or the weakly estrogenic pesticide methoxychlor could masculinize and/or defeminize the behavior of female hamsters. Neonatal hamsters were given a single sc injection of either zearalenone (1 mg/pup), methoxychlor (1 mg/pup), 17 beta-estradiol (E2) (40 micrograms/pup), or the vehicle 2 days after birth. After puberty, behavioral estrous cyclicity was measured. The females were then ovariectomized, treated with the male hormone testosterone, and tested for their ability to mount a receptive female (a behavior not normally displayed by female hamsters). Females treated neonatally with estradiol or zearalenone were masculinized but not defeminized, an effect consistent with perinatal exposure to low doses of sex hormones. Females in these two treatment groups displayed normal 4-day behavioral estrous cycles, but following ovariectomy and testosterone treatment they mounted a sexually receptive female at a frequency comparable to the males. Methoxychlor-treated females did not differ from controls. The mounting behavior of similarly treated males was unaffected by any of the chemicals. However, males receiving estradiol treatment had smaller testes, seminal vesicles, and cauda epididymides and 57% had epididymal cysts. These results demonstrate that a single exposure to a weakly estrogenic chemical like zearalenone during a critical developmental period can cause the brain to differentiate in a manner inconsistent with the female's genetic sex. This enables the female to respond to the activational influence of testosterone as an adult and readily mount a sexually receptive female. The failure of methoxychlor to alter reproductive development in the current study may be due to an inability of the neonatal hamster to convert methoxychlor to estrogenic metabolites.

Effect of tamoxifen on H-Y antigen expression and gonadal development in chicken embryos

Avian species follow the ZW/ZZ system of sex determination, which the female is heterogametic and expresses H-Y (or, more appropriately, 'H-W') antigen. We present the results of an investigation into the effects of the antiestrogen, tamoxifen, on gonadal differentiation and H-Y antigen expression in chickens. When given at doses of 0.25-2 mg per egg immediately before incubation, tamoxifen blocked regression of the right gonad in a significant number of 14-day-old female embryos. The nonregressed right gonad had a testis-like external appearance and, in some cases, contained what appeared to be spermatogenic tubules. Tamoxifen had no histologically detectable effect on the differentiation of the left ovary or the testes. In spite of tamoxifen's histological effects on right female gonads, it did not masculinize the steroidogenic capabilities of these gonads. Whether obtained from drug- or vehicle-treated embryos, the left and right female gonads always contained appreciable amounts of estrogen. In contrast, testes obtained from either drug- or vehicle-treated embryos did not contain detectable amounts of estrogen. Tamoxifen reduced the H-Y antigen levels in female liver and gonads. In both left and right female gonads, the reduction was to male levels. In female livers, tamoxifen reduced H-Y antigen to levels intermediate between those of normal males and females. Thus, the expression of H-Y antigen in both gonadal and nongonadal tissue is estrogen dependent, but the dependency appears to be more stringent for gonadal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase of lymphocytic H-Y antigen in female 21-hydroxylase deficiency

H-Y antigen was found to be increased in lymphocytes from 10 female 21-hydroxylase deficiencies, suggesting a correlation between the degree of virilization of these patients and their H-Y + lymphocytes proportions. Furthermore, these findings demonstrate the ability of a 46,XX female subject to produce, in some circumstances, an excess of H-Y antigen.

Extensive sequence homologies between Y and other human chromosomes

Twenty-six human Y-chromosome-derived DNA sequences, free of repetitive material, were used to probe male and female genomic blots. We present data from a detailed analysis and chromosomal location of the bands detected by such probes, which demonstrate extensive DNA sequence homology between the mammalian sex chromosomes and autosomes. Under stringent conditions, nine Y-derived probes reacted exclusively with the Y chromosome, 12 probes detected homologous sequences present on both the Y and the X, four probes detected homologies between Y and autosome(s) without any X counterpart and, finally, one probe hybridized to homologous sequences on Y, X and autosome(s). These data are consistent with the hypothesis of a common evolutionary origin for the mammalian sex chromosomes and reveal structural similarities between Y-located and autosomal non-repetitive sequences.

Human XX males with Y single-copy DNA fragments

In humans, XX maleness is the best known example of a sex reversal syndrome occurring with an incidence of one XX male among approximately 20,000 to 30,000 newborn boys. The karyotypes of the majority of these individuals are apparently normal, with respect to the numbers and structure of the chromosomes, but is in contradiction with the phenotypic sex which they display. XX maleness may be either a non Y-related mechanism triggered by a mutation on another chromosome or could be the result of the expression of some cytogenetically undetectable Y chromosome material present in the genome of such individuals. Recently, a number of human Y-specific single copy probes have been isolated. In this study, using several of these Y-specific probes we definitively demonstrate the presence of Y-chromosomal material in the genome of some 46,XX human males. These XX males carry only a fraction of the human Y chromosome. In the three positive cases reported here, presence of inclusive overlapping chromosomal fragments has been detected, implying a genetic heterogeneity of these patients.

Oocyte production in a Turner syndrome patient with serologically detectable male antigen

A patient with a 45,X/46,X, ring (X) karyotype has been found with serologically detectable male antigen, functioning ovaries, and documented oocyte production.

Cytomegalovirus infection of murine testicular interstitial Leydig cells

We studied the susceptibility of mouse testicular interstitial Leydig cells to cytomegalovirus both in vivo and in vitro. The in vivo studies included intratesticular and intraperitoneal infection of 6-week-old mice with murine cytomegalovirus (MCMV); the in vitro studies involved an MCMV-Leydig cell interaction using a Leydig tumor cell line (I-10). MCMV-specific antigens were detected in interstitial Leydig cells in sections of MCMV-inoculated testes by an indirect immunofluorescence test. MCMV DNA was also localized in the same testes cells derived from mice, which received intratesticular and intraperitoneal MCMV inoculations, respectively, by in situ DNA-RNA hybridization. Cytopathic effects were seen in MCMV-infected I-10 cell cultures 2 or more days after exposure to MCMV. The infected cells showed intranuclear inclusions characteristic of cytomegalovirus when stained with May-Grunwald-Giemsa stain. The indirect immunofluorescence test was also positive with MCMV-infected I-10 cells. MCMV DNA was detected in these cells by in situ DNA-RNA cytohybridization, and the presence of viral particles in MCMV-infected I-10 cells was confirmed by electron microscopy. Thus, we conclude that the interstitial Leydig cell is susceptible to MCMV infection both in vivo and in vitro.

Isolation of recombinant bacteriophage containing male-specific mouse DNA

The mammalian Y chromosome is an isolated piece of genetic material that directs sexual determination and gametogenesis. Very little is understood about the mechanism whereby the Y chromosome carries out these functions. Also, there is a severe lack of genetic markers on this chromosome. In order to understand the structure and function of the Y chromosome at the level of its DNA sequences and to provide genetic markers, we are isolating clones of DNA whose sequences are found primarily in DNA from male mice. To this end, we have developed a procedure for the identification of such clones. Application of this screening procedure to a lambda library derived from mouse sperm DNA has yielded 12 distinct clones, part of whose sequences are present predominantly in male DNA. Besides this DNA, they also contain other sequences that are shared with female DNA. These clones are either derived from the Y chromosome or they represent autosomal sequences specifically amplified during male development.

Translocation(X;Y)(p22.33;p11.2) in XX males: etiology of male phenotype

Analysis of G-banded prometaphase chromosomes from three XX males revealed extra bands on the distal end of one X short arm. These bands were similar both in size and staining properties to the distal Y short arm of their fathers (in the two cases examined) and also to other chromosomally normal males. The extra material on the abnormal X chromosomes was not C- or G-11 positive in the two cases examined, suggesting that the proximal Y long arm was not present. Previous karyotype-phenotype correlations with structurally altered Y chromosomes provided evidence for localization of male determinants on the Y short arm. The present findings in XX males provide support for more precise localization, to bands p11.2 leads to pter of Y short arm.

Hormones and psychosexual differentiation: implications for the management of intersexuality, homosexuality and transsexuality

During fetal development of subprimate mammals, sexual differentiation of the genitals and of specific sex-dimorphic brain systems depends on androgens; corresponding sex differences are displayed in prepubertal behaviours as well as in behaviours that depend on activation by pubertal hormones. In human beings, fetal hormones play the same role in genital differentiation. Hormone-dependent structural brain changes are also very likely but have not yet been demonstrated. The corresponding effects of fetal hormones on childhood behaviour have been found both in subhuman primates and in man, while the evidence concerning later behaviour, including sexual orientation, is not yet clear. The development of gender identity in humans is a cognitive process that has no counterpart in animal behaviour and is unlikely to be based on a specific hormone-sensitive brain system. It appears that the hormone-dependent variations of sex-dimorphic behaviour in childhood can be accommodated within either gender identity, provided that the child's physical appearance is gender adequate and the parental (or other caregivers') rearing style does not interfere with typical gender role development. In intersex individuals, changes in gender identity seem to occur primarily when genital and/or general physical appearance are in conflict with the assigned gender and/or when rearing has been ambiguous. The available descriptions of such changes do not seem compatible with a primarily neuroendocrine explanation. Thus, decisions on sex assignment and reassignment of intersex patients need to be based on expected social and sexual functioning, and the clinical management of such patients must minimize the risk of ambiguous rearing and of the development of a gender-incongruent physical appearance. The development of a sexual orientation in humans as hetero- or homosexual does not seem to depend on pubertal hormones. The evidence for a role of fetal hormones is suggestive, but the issue is not yet settled. Attempts to implicate the H-Y antigen in the aetiology of transsexuality seem to have failed; psychoendocrine research here parallels that on sexual orientation. Some recent developments in the management of transsexual patients are discussed.

H-Y antigen expression in patients with X-autosomal translocations and gonadal dysgenesis

Cells from three patients with early gonadal failure and a balanced reciprocal translocation involving the long arm of the X chromosome and an autosome were studied. Fibroblasts from a patient with a similar balanced reciprocal translocation but normal reproductive capabilities were also studied. Two of the four patients were found to have serologically detectable H-Y antigen on their cells. Since H-Y antigen has been found on the cells of other patients with X chromosome abnormalities but without a Y chromosome, it is thought that the X chromosome plays a role in the regulation of H-Y antigen expression. This study suggests that the long arm of the X chromosome may be involved but the location of a regulatory gene cannot be identified in these studies. These cases do not permit us to implicate H-Y antigen as a cause of gonadal dysgenesis and early gonadal failure in females who have structurally abnormal X chromosomes.

Dysgenesis of testicular and streak gonads in the syndrome of mixed gonadal dysgenesis: perspective derived from a clinicopathologic analysis of twenty-one cases

The clinical and pathologic aspects of 21 cases of mixed gonadal dysgenesis (MGD) were studied. The gonads in 15 patients consisted of a macroscopic testis and a streak gonad; six patients had variants, including two with bilateral testes and four with bilateral streak gonads or tumors. Functionally, the gonads were incompetent. Testes 1) failed to completely inhibit müllerian development, 2) failed to support full differentiation of mesonephric duct structures, 3) failed to adequately masculinize development of the external genitalia, or 4) often failed to mediate their own descent, resulting in asymmetry of the internal and external genitalia. None of the streak gonads mediated normal female adolescent development or fertility. Microscopic examination revealed that every gonad, regardless of its gross appearance, was morphologically abnormal. Although gonads with seminiferous tubules usually developed to a moderately advanced state, macroscopically resembling testes, the hilar zone remained architecturally disorganized; the cortex invariably lacked more than a rudimentary tunica albuginea or exhibited partial ovarian differentiation, sometimes even with a rare primordial follicle. Over time, the seminiferous tubules atrophied and hyalinized. Gonads that grossly resembled streak gonads were observed microscopically to be composed of a stroma resembling that of normal ovarian cortex. In patients more than several years of age, the entire complement of germ cells in streak gonads disappeared. It is suggested that patients with MGD be raised as females. Early removal of gonads will prevent the development of gonadoblastoma and dysgerminoma. If the uterus is retained and the patient is subsequently given exogenous estrogen, care should be taken to detect early any signs of the development of endometrial carcinoma or its precursor, to which these patients may be prone.

Modifications of chromatin structure in control of gene expression

Repetitive sequences in intron and spacer DNA could be sites for binding of chromosomal proteins which maintain chromatin structure and control gene activity. Methylation of DNA guides the binding of acidic nonhistone proteins and maintains the differentiation state during DNA replication. Differentiation inducers modify repressor proteins permitting unfolding of chromatin. Histone H 1 must be removed for gene activity. Phosphorylation of nonhistone proteins probably induces allosteric modifications which permit unfolding of chromatin. Acetylation of nucleosomal histones is necessary to permit passage of RNA polymerase. Deacetylation quickly returns the gene to a normal histone repressed state. Chromosomal RNA attached to nonhistone proteins aids the binding of RNA polymerase to the DNA template. Carcinogens can disrupt normal gene control leading to circumvention of normal cell cycle controls.

Presence of H-Y antigen in patients with Ullrich-Turner syndrome and X-chromosome rearrangements

Cells from eight of ten patients with gonadal dysgenesis and an isochromosome for the long arm of X, (i(Xq)), have been found to be H-Y antigen-positive, using an assay that employs rat antiserum and Raji cells. In addition, two patients with del(Xq) were also found to be H-Y antigen-positive, whereas four patients in whom only a 45,X line was detected were H-Y antigen-negative. These findings suggest that the X chromosome plays a role in the expression of H-Y antigen in the absence of a Y chromosome. Since our patients with i(Xq) show no evidence of testicular differentiation, it is clear that there is not enough H-Y antigen on these patients' cells to direct the development of a testis. These findings are consistent with the view that the normal functioning of genes on the X and the Y chromosomes is necessary for testicular organogenesis to occur.

Effects of prenatal sex hormones on gender-related behavior

Gender identity depends largely on postnatal environmental influences, while sex-dimorphic behavior and temperamental sex differences appear to be modified by prenatal sex hormones. A role of the prenatal endocrine milieu in the development of erotic partner preference, as in hetero-, homo-, or bisexual orientation, or of cognitive sex differences has not been conclusively demonstrated.

Testosterone: a major determinant of extragenital sexual dimorphism

Sexual dimorphism in selected extragenital tissues is described with emphasis on the molecular basis of the differences. Testosterone rather than 5 alpha-dihydrotestosterone appears to be the major intracellular androgen in organs other than skin and reproductive tract, but other steroid metabolites and their receptors are required to produce the diverse tissue differences observed in males and females. There is also evidence that multiple hormones from several endocrine glands are required to act in concert with androgens to produce and maintain their effects. Although many of the consequences of sexual dimorphism, such as body size and strength, have been evident for centuries, other differences between males and females such as disease incidence, response to drugs and toxins, and the metabolism and assimilation of dietary constituents have only recently been discovered.