Major regulatory genes for mammalian sexual development

Transcriptional and epigenetic networks of helper T and innate lymphoid cells

The discovery of the specification of CD4(+) helper T cells to discrete effector 'lineages' represented a watershed event in conceptualizing mechanisms of host defense and immunoregulation. However, our appreciation for the actual complexity of helper T-cell subsets continues unabated. Just as the Sami language of Scandinavia has 1000 different words for reindeer, immunologists recognize the range of fates available for a CD4(+) T cell is numerous and may be underestimated. Added to the crowded scene for helper T-cell subsets is the continuously growing family of innate lymphoid cells (ILCs), endowed with common effector responses and the previously defined 'master regulators' for CD4(+) helper T-cell subsets are also shared by ILC subsets. Within the context of this extraordinary complexity are concomitant advances in the understanding of transcriptomes and epigenomes. So what do terms like 'lineage commitment' and helper T-cell 'specification' mean in the early 21st century? How do we put all of this together in a coherent conceptual framework? It would be arrogant to assume that we have a sophisticated enough understanding to seriously answer these questions. Instead, we review the current status of the flexibility of helper T-cell responses in relation to their genetic regulatory networks and epigenetic landscapes. Recent data have provided major surprises as to what master regulators can or cannot do, how they interact with other transcription factors and impact global genome-wide changes, and how all these factors come together to influence helper cell function.

Putting the heat on sex determination

Sex determination and differentiation are inherently fascinating to both layperson and geneticist. Major advances have accelerated interest in the molecular genetic events mediating these processes in nematodes, flies, mice and humans. Far less attention has been paid to those organisms, particularly reptiles, where sex is determined by environmental cues. However, recent experimental evidence suggests that the two modes of sex determination may not only share common genetic elements, but may also be regulated by similar mechanisms. We argue that the ability to manipulate sex by temperature provides a particularly suitable model for exploring the molecular basis of this fundamental biological process.

Sex inversion as a model for the study of sex determination in vertebrates

As a consequence of genetic sex determination, the indifferent gonadal blastema normally becomes either a testis or an ovary. This applies to mammals and to the majority of non-mammalian vertebrates. With the exception of placental mammals, however, partial or complete sex inversion can be induced in one sex by sexual steroid hormones of the opposite sex during a sensitive period of gonadogenesis. There is evidence that also during normal gonadogenesis in these species, in the XY/XX mechanism of sex determination testicular differentiation is induced by androgens, and in the ZZ/ZW mechanism, ovarian differentiation by oestrogens. In either case, the hormones may act via serological H-Y antigen as a morphogenetic factor. In contrast, in placental mammals including man, primary gonadal differentiation is independent of sexual steroid hormones, and factors directing differential gonadal development have not yet been conclusively identified. However, various mutations at the chromosome or gene level, resulting respectively in sex inversion or intersexuality, have provided clues as to some genes involved and their possible nature. In this context also, serological H-Y antigen is discussed as a possible factor acting on primordial gonadal cells and inducing differential growth or morphogenesis or both. The data available at present allow a tentative outline of the genetics of sex determination in placental mammals.

An in vitro model of gonad differentiation in the chick embryo. Roller cultures in gas permeable biofoil bags

Embryonic gonads of 6 1/2 to 12 days old chick embryos were enzymatically dissociated. The cell suspensions were cultured in small gas permeable bags of foil (Biofolie Heraeus) in a roller culture apparatus. The cells formed multiple small aggregates, in which sex specific differences developed within two days. In cell suspensions of embryonic testes smooth spheric aggregates formed with well delineated testicular cords in the center and a tunica albuginea-like mesenchymal layer at the outside. Most of the male germ cells were incorporated in the central cords. A number of germ cells were barred from entering the cords by the tunica albuginea-like mesenchymal layer and populated the outer surface of the aggregates. The aggregates of left ovary were irregular in shape and characterized by clusters of germ cells residing in an outer cortical zone. The aggregates of the right ovary, which regresses in vivo, showed poor growth and did not differentiate, thus, indicating that the suppression of right ovary was not removed in culture. In the roller cultures of dissociated embryonic gonads male and female morphogenesis was mimicked in a reproducible manner, so that the system can be used for further experimental studies of gonadal development.

Inhibition of growth and differentiation of fetal hamster gonads grafted into the adult testis

A cytomorphological analysis of the effect of adult testes on growth and differentiation of grafted fetal testis or ovaries was performed in hamsters. Fetal gonads, taken at 14 days post-coital age, were grafted for 30 days either under the renal capsule or testicular capsule of scrotal or cryptorchid testes of adult hamsters (weight 115 +/- 23 g). Renal grafts were also performed in males castrated 30 days prior to receiving the fetal gonads. Growth and differentiation of the fetal gonads (testis or ovary) was totally inhibited by the scrotal testis. When the cryptorchid testis was the recipient of fetal gonads, inhibition was correlated inversely with the degree of spermatogenic damage elicited in the cryptorchid testis. No inhibition was observed in fetal gonads grafted under the kidney capsule, nor in castrated, normal or cryptorchid animals. As normal growth and differentiation of both testis and ovary occurred when grafted under the kidney capsule, the inhibitory effect of adult gonads seems to be unrelated to plasma testosterone levels in the host, as levels were undetectable in castrated hamsters and reduced drastically in cryptorchid animals. At the same time, the testicular-inhibiting substance in normal animals did not act at a distance, since its effect was restricted to fetal gonads grafted under the testicular capsule. This inhibitory substance may correspond to the spermatogonial chalone, known to be produced by differentiating spermatogenic cells (mainly spermatocytes and round spermatids in the rat and mouse); these chalones prevent spermatogonial proliferation and, consequently, the critical number of spermatogonia needed to enter meiosis is not attained. It is doubtful if the same substance has the ability to differentiate the fetal ovary or if this effect can be ascribed to a more complex situation involving other testicular peptides of paracrine action and/or locally high levels of androgens.

Serological H-Y antigen in the female chicken occurs during gonadal differentiation

In the chicken, serological H-Y antigen is specific for the female sex. Male gonad differentiation can be experimentally influenced by estrogens, resulting in the transient formation of an ovotestis. The sex-inverted gonad becomes positive for H-Y antigen. Therefore, the question arises whether, in normal gonadogenesis also, the female gonad at the indifferent stage, before estrogens are produced, is negative for H-Y antigen. Here we show that this is indeed the case. The female gonad becomes positive for H-Y antigen when the ovary starts its organotypic differentiation at about day 6 1/2 of embryonal development. It is assumed that estrogens are responsible for the occurrence of H-Y antigen. This finding supports the view that H-Y antigen plays a role in primary ovogenesis in the chicken.

An in vitro model of gonad differentiation in the chicken. Estradiol-induced sex-inversion results in the occurrence of serological H-Y antigen

Dissociated cells from the gonads and mesonephros of 8-day-old chicken embryos were reorganized in rotation culture. The aggregates obtained from gonadal cells exhibited specific morphologic and histologic sex differences. In the presence of estradiol, aggregates from testicular cells showed characteristics similar to control ovarian aggregates, while in ovarian aggregates under estradiol treatment the female organization became more pronounced. Determination of serological H-Y antigen revealed that male aggregates of gonads and mesonephros were negative for H-Y and those of female embryos were positive for H-Y. Administration of estradiol did not change the H-Y findings in female aggregates. In contrast, in the male, gonadal cultures became H-Y positive while mesonephros cultures remained negative. It is assumed that estradiol induces the occurrence of H-Y antigen in the gonads.

Absence of Y-specific DNA sequences in human 46,XX true hermaphrodites and in 45,X mixed gonadal dysgenesis

A search for Y-specific DNA sequences has been performed in a sample of seven 46,XX true hermaphrodites and one 45,X mixed gonadal dysgenesis case and compared with a sample of 11 XX males. Using six Y-specific DNA probes no hybridization signal was obtained in the hermaphrodite group; in contrast, all XX males gave a positive signal with at least one probe. This difference is statistically highly significant. We conclude that the aetiology of true hermaphroditism is different from that of the XX male syndrome. As all cases of the hermaphrodite group are positive for the serological sex-specific antigen (Sxs) it is concluded that this antigen can be present even in the absence of Y-specific DNA.

Diagnostic applications of H-Y serology: H-Y negative phenotype in cells from 45,X/46,XY fetus with testes

Sexual dysmorphism should be considered likely in cases in which H-Y- phenotype and XY complement are found together. In the case described here, a pregnancy was terminated at nineteen weeks of gestation after 45,X and 46,XY cell lines were detected among cultured amniocytes. The fetus was a male with hypospadias and intraabdominal testes containing irregular tubules and hyperplastic interstitium. Cultured skin fibroblasts, containing 45,X and 46,XY lines in ratio of 18:2, were typed H-Y antigen negative. This underscores the danger of predicting gonadal type on the basis of somatic H-Y phenotype.

Reaggregates of cells from rat testis resemble developing gonads

Reaggregates prepared from newborn rat testis cells in Moscona-type rotation cultures were analyzed and compared with normal fetal (12-21 days) and newborn testes at the light and electron microscope level. After 25 h of culture, the aggregates resembled normal testicular tissue. The cells of the surface layer were spindle-shaped and connected by adherent junctions. The epithelial cords were composed exclusively of Sertoli cells and were surrounded by elongated cells resembling the developing myoid cells in newborn testes. The basal aspect of the cords was covered by a layer of flocculent material which, in places, was organized like an ordinary basement membrane. Individual spermatogonia with pseudopodes were observed in the interstitial tissue. Some Leydig cells were organized into small clusters like those typical in newborn testes. The present observations indicate that, histologically, the reaggregation of separated testicular cells resembles the differentiation of embryonic male gonads.

H-Y antigen expression in heterogametic males (XY) and females (ZW): a factor in reproductive strategy?

The cells of heterogametic females with ZW sex chromosomes express H-Y or H-W antigen. A hypothesis is formulated to explain why these animals are capable of 'practicing' amphigonia retardata, i.e., delay in actual fertilization of eggs by retaining viable sperm within the oviduct for a considerable time (several months).

Evidence of a preferential inactivation of the paternally derived X chromosome in a 46,XX true hermaphrodite

The pattern of inheritance of several X polymorphic markers is studied in the pedigree of a 46,XX true hermaphrodite. The results of the Xga, 12E7, and G6PD segregation analysis favour the hypothesis of a preferential inactivation of the paternally derived X chromosome.

Absence of H-Y antigen in a case of sporadic pure gonadal dysgenesis

H-Y activity, endocrine function and gonadal histology were studied in a phenotypic female presenting with features of sporadic 46,XY pure gonadal dysgenesis. H-Y activity was absent, hormonal data revealed a primary ovarian failure with a blunted response of FSH to LHRH; there was no testicular tissue nor microscopic evidence of gonadal tumor in the gonads. The current view on the role of H-Y antigen in the differentiation of the gonads and in the occurrence of gonocytoma is discussed.

Analysis of male sterile mutations in the mouse using haploid stage expressed cDNA probes

A differential hybridization screening procedure has identified cDNAs which correspond to RNAs which are expressed in mouse testis and at lower levels in liver and spleen. The sensitivity of this procedure is such that approximately 0.5% of 1.4 X 10(4) cDNA clones are revealed as "testis specific". We have focused on ten cDNA clones which have been used to identify RNAs expressed in the haploid phase of spermatogenesis. Using Northern blots to analyse RNA isolated from the testes of mutant mice (Tfm/Y and Sxr/+) blocked at specific stages in spermatogenesis or RNA from sexually immature mice, 8 clones have been identified which correspond to RNAs expressed uniquely or at much higher levels in meiotic or post meiotic cells.

Reduced fertility in women with X chromosome abnormality

One patient with the karyotype 46,X,del(X)(p11.23) and three patients with 45,X/46,XX mosaicism were fertile or showed normal ovarian function. The patient with the Xp deletion has two daughters with the same chromosomal abnormality. A study of these patients and of others reported in the literature indicated that fertility of patients with X chromosomal abnormality has a markedly shorter duration than fertility of the normal female. Menopause commonly occurred during the second and third decade of age. We suggest that such fertility is related to the rate of germ cell attrition and hypothesize that germ cell attrition in the human female is influenced by genes of multiple effect which are carried on the X chromosome. The more of these genes which are present the slower the rate of germ cell attrition.

Protein A radio-assay of H-Y antigen on human leukocytes using mouse and rat antisera and monoclonal antibodies

The presence of H-Y antigen on human leukocytes was investigated using a protein A radio-assay. H-Y antigen could be demonstrated on male cells using either conventional H-Y antisera produced in mice and rats, or monoclonal H-Y antibodies. With mouse antiserum and IgG-type monoclonal antibody the reaction was male-specific using a single antibody. The reaction obtained with rat antiserum was enhanced by the application of a second antibody (rabbit anti-mouse IgG). This technique provides a rapid, simple, objective, and semiquantitative method for the determination of cellular H-Y antigen, the results being expressed as radioactivity bound to the test cells and thus being independent of human observation. It requires only 10-20 ml of blood and small quantities of antiserum or antibody.

The H-Y antigen and its functions: a review and a hypothesis

Having reviewed the status of H-Y as the sex-determining antigen concerned with the differentiation of the dominant gonad, we consider some of the problems deriving from the tests for this antigen, and from their application to the study of natural experiments. To reconcile the results of these studies with the alleged influence of H-Y on gonadal development, we propose and discuss a hypothesis on the genetic control of the synthesis of this antigen. This states that an autosomally-coded, positively cross-reacting precursor is rendered biologically active by a Y-chromosomal gene, and transformed (in a dose-dependent manner) into a biologically inactive, antigenically negative substance under the influence of an X-chromosomal gene.

Morphogenesis and fibronectin in sexual differentiation of rat embryonic gonads

The possible role of fibronectin in the organization of the sex-specific gonadal components was studied by immunocytochemistry combined with electron and light microscopy in rat fetuses at the ages of 12-15 days. Fibronectin was evenly distributed in both sexes under the basal lamina of the surface epithelium. Other basal laminae were not seen using light or electron microscopy inside the gonadal ridges at the age of 12 days. As the first sign of sexual differentiation, fibronectin-negative gonadal cords appeared in 13-day-old fetuses. In the males the cords were bigger than those in the females. The cords were clearly separated from the interstitium in 15-day-old fetuses of both sexes. A continuous layer of fibronectin had formed between the testicular surface epithelium and the elongated cords indicating the formation of a tunica albuginea. In females the surface epithelium-cord connection was maintained at all stages. Connections of the gonadal cords to mesonephric tubuli were seen in the rete region of both sexes. The electron optical basal lamina around the gonadal cords became continuous by the age of 15 days. The present results suggest that fibronectin is intimately involved in the sexual differentiation of the gonads, but not under the regulation of H-Y antigen or other testis-organizing factor.

Genetic homology and crossing over in the X and Y chromosomes of Mammals

The "X-Y crossover model" described in this paper postulates the (1) the pairing observed between the X and the Y chromosome at zygotene is a consequence of genetic homology, (2) there is a single obligatory crossover between the X and Y pacing segments, and (3) the segment of the X which pairs with the Y is protected from subsequent inactivation. Genes distal to the proposed crossover ("pseudoautosomal genes") will appear to be autosomally inherited because they will be transmitted to both male and female offspring. Some criteria for identifying pseudoautosomal genes are outlined. The existence of a single obligatory crossover between the X and Y of the mouse is strongly supported by a recent demonstration that the sex-reversing mutation Sxr, which is passed equally to XX and XY offspring by male carriers, is transmitted on the sex chromosomes. Pseudoautosomally inherited genes may also be responsible for XX sex reversal in goats and familial XX sex reversal in man.

Dysgerminoma--gonadoblastoma and familial 46XY pure gonadal dysgenesis: case report and review of the genetics and pathophysiology of gonadal dysgenesis and H-Y antigen

46XY gonadal dysgenesis is a rare condition of intersexuality first described in detail by Swyer in 1955. It is characterized by a phenotypic female who is tall, eunuchoid with normal female external genitalia, hypoplastic uterus and Fallopian tubes, streak ovaries and primary amenorrhoea. The patients exhibit none of the associated congenital defects such as webbing of the neck and genu valgum seen in Turner's syndrome. Although rare, this clinical entity is important to recognize because of the high incidence of gonadoblastomas and subsequent development of dysgerminoma. The condition may be familial and therefore siblings need to be screened. To the geneticists and scientists researching in the area of intersexuality, hermaphroditism and sexual determination, it has helped to unveil the mechanisms of gonadal and genital sexual development.

beta 2-Microglobulin and its relationship to the immune system

beta 2-Microglobulin has been isolated from several species, but only bovine beta 2-microglobulin, previously known as lactollin, has been crystallized. An improved method for its isolation from colostrum is described. The bovine homologue exhibits a concentration-dependent aggregation behavior. beta 2-Microglobulin is related to both immune and histocompatibility antigen systems. It exhibits homology with the constant domains of the immunoglobulin-G light and heavy chains and is an integral part of histocompatibility antigens bound to cell surface. beta 2-Microglobulin also occurs in the free state in various body fluids including milk and colostrum. The possible relationship of elevated free beta 2-microglobulin of pathological conditions is suggested for future research.

A protocol for detection of H-Y antigenic variants

A skin grafting protocol is described for finding H-Y antigenic variants. The method is applicable regardless of the location of the structural gene(s) for this antigen (X, Y, or autosomal). Use of this protocol revealed no evidence for H-Y antigenic variation between C57BL/6J and strains 129/J, A.BY/SnJ, C3H.SW/SnJ, and LP/J.

Cell reorganization in vitro of heterosexual gonadal cocultures

Male and female gonadal cells of newborn rats were cocultured in varying proportions. As low a proportion as 20% of male cells essentially yielded tubular structures. At lower quotas of testicular cells, however, only follicular structures occurred. Mixed structures were not observed except one experiment (20% male cells). When ovarian cells were cocultivated with male nongonadal cells, no conversion occurred. It is assumed that H-Y antigen secreted by male gonadal cells is bound by the ovarian receptor sites and induces conversion into tubular structures. H-Y antigen integrated into the cell membrane of nongonadal male cells does not seem to be able to exert this morphogenetic effect.

H-Y antigen expression in different tissues from transsexuals

H-Y-antigen expression was analyzed in patients with transsexuality. Peripheral blood lymphocytes and various tissues were examined using the cytotoxicity assay of Goldberg et al. (1971). Peripheral blood lymphocytes from healthy male and female subjects were used as controls as well as tissues from non-transsexual individuals and from male and female C57B1/6J mice. In three female-to-male transsexuals the peripheral blood lymphocytes were H-Y antigen positive. In these patients also their ovaries, uterus, and mammae were found to be H-Y antigen positive. Three male-to-female transsexuals were examined. The peripheral blood lymphocytes in two of these patients were found to be H-Y antigen negative. Their testes were also H-Y antigen negative, as well as the epididymus, the corpus cavernosum penis, and the cremaster muscle which was analyzed in one of them. One male-to-female transsexual had peripheral blood lymphocytes which were H-Y antigen positive; this patient had testis and corpus cavernosum penis which were also H-Y-antigen positive.

Genetic heterogeneity of XY gonadal dysgenesis (Swyer syndrome): H-Y antigen-negative XY gonadal dysgenesis associated with inflammatory bowel disease

A 16 1/2-year-old girl was studied because of ileitis, lack of pubertal development, and primary amenorrhea. She had a 46,XY chromosome constitution in lymphocytes in fibroblasts without structural defects of X or Y. She was H-Y antigen negative. This observation supports the concept of causal heterogeneity of XY gonadal dysgenesis (Swyer syndrome). Two groups have been established: (1) H-Y antigen-positive forms, which are more common, possibly due to gonad-specific receptor defects (total failure or reduced receptor affinity), (2) H-Y antigen-negative forms possibly due to mutation in the H-Y generating system, either of the structural gene (presumably autosomal) or of a controlling gene (on the sex chromosomes). The H-Y antigen status may be of value in determining which patients are at risk for gonadoblastoma or dysgerminoma.

Mammalian cross-reactive H-Y antigen induces sex reversal in vitro in the avian testis

Testes of either newborn rats or newly hatched chickens, dissociated into single cell suspensions, reorganize in vitro into their histotypic structures. In birds, the heterogametic female sex is H-Y antigen positive, and not the male as in mammals. Cocultivation of rat and chicken testicular cells results in the reorganization of an ovotestis. A similar result is obtained after cultivation of chicken testicular cells in the supernatant medium of cultured human male Burkitt lymphoma Daudi cells. Rat testicular Sertoli cells as well as Daudi cells are a source of H-Y antigen. The simultaneous application of H-Y antigen and anti-H-Y antiserum prevents ovotestis formation. It is concluded that H-Y antigen which is known to be testis-organizing in mammals, is the ovary-organizing factor in birds.

H-Y antigen in transsexuality, and how to explain testis differentiation in H-Y antigen-negative males and ovary differentiation in H-Y antigen-positive females

H-Y antigen was determined in eight transsexual patients. Two of the four male-to-female transsexual patients typed as H-Y antigen-negative, while the other two typed as expected from their phenotypic and gonadal sex, namely H-Y antigen-positive. Of the four female-to-male transsexual patients, three typed as H-Y antigen-positive and one was H-Y antigen-negative, as expected. The presence of normal testes in H-Y antigen-negative males is assumed to result from a mutation of nucleotide sequences of the H-Y structural gene for antigenic determinants. Thus, an H-Y is produced with normal receptor-binding activity which can sustain the testis determination of the bipotent gonadal anlage. In the case of H-Y antigen-positive females with normal ovaries a deletion of the autosomally located H-Y structural gene is assumed. This deletion should affect sequences for repressor-binding (as was suggested for H-Y antigen-positive XX-males) and for receptor-binding activity of the H-Y antigen molecule. The resulting H-Y antigen is unable to bind to the gonadal receptor of the bipotent gonadal anlage. Thus an ovary is determined. The relevance of H-Y antigen for the aetiology of transsexualism is discussed.

Gonadal dysgenesis in a 46,XY female mosaic for double autosomal trisomies 8 and 21

The proband was evaluated at 19 years of age because of primary amenorrhoea and, on chromosomal analysis, was found to have a 46,XY karyotype in 75% of her cells and 48,XY, +8, +21 in 25% of her cells. She appeared normal at birth and exhibited normal intellectual and physical development until puberty when secondary sexual differentiation failed. This young women showed none of the dysmorphic features associated with either trisomy 8 or trisomy 21. Her XY gonadal dysgenesis was manifested by late developmental problems of amenorrhoea, sexual infantilism, and gonadal neoplasia.

A synopsis of the human Y chromosome

Phenotypic features and functions known to depend on the presence of the Y chromosome or the H-Y antigen are discussed in relation to structural anomalies of the Y chromosome and other abnormalities of sexual and somatic development. Recent knowledge about molecular organization of constitutive heterochromatin in relation to the human Y is presented. An attempt is made at assigning different functions, genes and DNA sequences to different regions of the Y chromosome.

Inhibition of testicular organization in vitro by newborn rat ovarian cell supernatants

Cell reorganization experiments performed with newborn rat gonadal single cell suspensions resulted in organ-like reorganization after 18 h of rotation culture. When, however, testicular cells were incubated in supernatants of newborn rat ovarian cells, testicular organization was suppressed and the architecture of the reorganized gonad was rather feminine. Supernatants of adult rat ovarian cells did not inhibit testicular organization. The possible mechanisms responsible for the failure of the function of H-Y antigen by the presence of ovarian cell supernatants of newborn rats are discussed.

Sexual characteristics of adult female mice are correlated with their blood testosterone levels during prenatal development

Mice produce litters containing many pups, and the female fetuses that develop between male fetuses have significantly higher concentrations of the male sex steroid testosterone in both their blood and amniotic fluid than do females that develop between other female fetuses. These two types of females differ during later life in many sexually related characteristics. Thus, individual variation in sexual characteristics of adult female mice may be traceable to differential exposure to testosterone during prenatal development because of intrauterine proximity to male fetuses.

A gene controlling H-Y antigen on the X chromosome. Tentative assignment by deletion mapping to Xp223

The existence of a strict correlation between presence of testicular tissue and presence of H-Y antigen in mammals and man leads to the conclusion that H-Y antigen is an essential differentiation factor in testicular morphogenesis. Presence of low titers of this differentiation antigen even in fertile females indicates that its morphogenetic effect depends on a threshold. Here, studies on H-Y antigen in female individuals with various deletions of the X-chromosome are reported. It turns out that deletion of Xp results in the synthesis of reduced amounts of H-Y antigen, while deletion of Xq does not. In a fertile female with only Xp223 deleted due to an X/Y translocation, including the distal Yq, presence of a reduced H-Y titer allows for the tentative assignment of a controlling gene repressing the H-Y structural gene. From the cases studied, it follows that the H-Y structural gene is autosomal and under the control of X- and Y-linked genes. The conception emerges that interaction between X- and Y-linked genes or their products results in variation of the H-Y antigen titer. The fate of the indifferent gonadal anlage to differentiate into the male or the female direction will depend on the titer of H-Y antigen reached by the action or interaction of the controlling genes involved.

Induction of H-Y antigen in the gonads of male quail embryos by diethylstilbestrol

In quails, H-Y antigen is induced by oestrogens in the gonads of the originally H-Y negative homogametic sex but not in non-gonadal tissues. This is consistent with the view that oestrogens act via H-Y antigen in the organization of the avian gonad.