XY Sex Reversal Research Articles

XY sex reversal associated with a deletion 5' to the SRY "HMG box" in the testis-determining region.

The human testis-determining factor resides within a 35-kilobase (kb) region of the Y chromosome immediately adjacent to the pseudoautosomal boundary. A candidate gene for human sex determination (SRY) was isolated in this region. Here, we describe a study of 25 cases of XY females with pure gonadal dysgenesis for mutations on the Y chromosome short arm, including SRY. Southern blotting revealed a sex-reversed female harboring a deletion extending from approximately 8 kb from the pseudoautosomal boundary of the Y chromosome to at least 33 kb and no more than 60 kb upstream, toward the centromere. The deletion begins no more than 1.8 kb upstream from the first ATG of the SRY open reading frame present in the clone pY53.3. To our knowledge, no mutation has been described previously outside the SRY "HMG box" on the short arm of the Y chromosome, which is associated with sex reversal. Since the 5' extent of the SRY transcriptional unit has not been defined, the deletion may remove upstream exons of SRY and/or transcriptional regulatory motifs, either situation resulting in lack of testicular development. It cannot be formally excluded that the mutation removes a second locus, independent of SRY, that is critical for sex determination. Denaturant gradient gel electrophoresis analysis of the SRY open reading frame in the remaining 24 cases revealed de novo single base-pair transitions in the SRY conserved domain in 4 cases.

XY Sex reversal associated with a nonsense mutation in SRY

Sex determination in humans is mediated through the expression of a testis-determining gene on the Y chromosome. In humans, a candidate gene for the testis-determining factor ( TDF) that encodes a protein with a putative DNA-binding motif and has been isolated is termed SRY. Here we describe an XY sex-reversed female with pure gonadal dysgenesis who harbors a de novo nonsense mutation in the SRY open reading frame ( SRY-orf). This single-basepair substitution results directly in the formation of a termination codon in the putative SRY DNA-binding motif, presumably leading to a nonfunctional gene product. This brings the number of reported XY sex-reversed females with de novo mutations in the known SRY-orf to three, each occurring in the putative DNA-binding domain. This provides further evidence to support SRY being TDF in humans and also indicates the functional importance of the putative DNA-binding domain of the SRY protein.

Abnormalities of human sex determination.

Cytogenetic and molecular studies in patients with abnormalities of sex determination have been the key to the isolation and investigation of candidates for the primary testis determining factor (TDF). A gene, SRY, isolated from the sex determining region of the Y chromosome within 5 kilobases of the pairing segment boundary, has been characterized recently which fulfils the expectations of TDF. It is expressed in the embryonic gonads at the critical time of differentiation; it is highly conserved among mammals; it has the structure of a transcription regulator; and mutations within its conserved domain are found in 10% of sex-reversed XY females. The murine homologue of this gene has been shown to cause sex reversal in XX embryos following injection of a 14 kb DNA fragment containing SRY into fertilized eggs. However, most XX true hermaphrodites and a proportion of XX sex-reversed males lack SRY despite the presence of testicular differentiation. It is postulated that the constitutive activation of an X-linked gene, TDF-2, normally regulated by SRY, is responsible for male differentiation in these cases. The female phenotype of XY individuals with duplications of Xp may be the result or deletion of disruption of TDF-2.

Mutational analysis of SRY: nonsense and missense mutations in XY sex reversal.

XY females (n = 17) were analysed for mutations in SRY (sex-determining region Y gene), a gene that has recently been equated with the testis determining factor (TDF). SRY sequences were amplified by the polymerase chain reaction (PCR) and analysed by both the single strand conformational polymorphism assay (SSCP) and DNA sequencing. The DNA from two individuals gave altered SSCP patterns; only these two individuals showed any DNA sequence variation. In both cases, a single base change was found, one altering a tryptophan codon to a stop codon, the other causing a glycine to arginine amino acid substitution. These substitutions lie in the high mobility group (HMG)-related box of the SRY protein, a potential DNA-binding domain. The corresponding regions of DNA from the father of one individual and the paternal uncle of the other, were sequenced and found to be normal. Thus, in both cases, sex reversal is associated with de novo mutations in SRY. Combining this data with two previously published reports, a total of 40 XY females have now been analysed for mutations in SRY. The number of de novo mutations in SRY is now doubled to four, adding further strength to the argument that SRY is TDF.

Molecular biology of disorders of sex differentiation.

Sexual ambiguity can be a difficult and sometimes confusing diagnostic problem in children. Recent developments in molecular biology have provided the opportunity to analyze the gene responsible for testicular determination, SRY, the androgen receptor gene and the gene encoding the cP450 enzyme specific for 21-hydroxylation, CYP21B, whose defects are responsible for congenital adrenal hyperplasia. Southern-blotting studies and PCR analyses of SRY, androgen receptor and CYP21B genes can be routinely used for the direct diagnosis of gonadal dysgenesis, androgen insensitivity syndromes and congenital adrenal hyperplasia, respectively. In sex-reversed XY females, several de novo mutations or deletions in the SRY gene have been reported. Defects in the human androgen receptor cause a spectrum of defects in male phenotypic sexual development associated with abnormalities in the receptor protein. Analyses of the androgen receptor gene structure have identified the causative mutation in some families: mutations that result in large-scale alterations of the structure of the androgen receptor, mRNA or gene mutations that alter the primary structure of the androgen receptor protein and mutations that alter the level of mRNA. The diversity of clinical phenotypes, apparent in 21-hydroxylase deficiency, is paralleled by a considerable degree of mutational heterogeneity in the CYP21 gene locus. Various changes causing severe 21-hydroxylase deficiency have been reported: point mutations, gene conversions and gene deletions. In conclusion, substantial progress has been made elucidating genetic defects causing sex reversal in XY females, the androgen insensitivity syndrome and congenital adrenal hyperplasia. Molecular genetics can also be applied for carrier identification and prenatal diagnosis.

Genetic evidence equating SRY and the testis-determining factor

The testis-determining factor gene (TDF) lies on the Y chromosome and is responsible for initiating male sex determination. SRY is a gene located in the sex-determining region of the human and mouse Y chromosomes and has many of the properties expected for TDF. Sex reversal in XY females results from the failure of the testis determination or differentiation pathways. Some XY females, with gonadal dysgenesis, have lost the sex-determining region from the Y chromosome by terminal exchange between the sex chromosomes or by other deletions. If SRY is TDF, it would be predicted that some sex-reversed XY females, without Y chromosome deletions, will have suffered mutations in SRY. We have tested human XY females and normal XY males for alterations in SRY using the single-strand conformation polymorphism assay and subsequent DNA sequencing. A de novo mutation was found in the SRY gene of one XY female: this mutation was not present in the patient's normal father and brother. A second variant was found in the SRY gene of another XY female, but in this case the normal father shared the same alteration. The variant in the second case may be fortuitously associated with, or predisposing towards sex reversal; the de novo mutation associated with sex reversal provides compelling evidence that SRY is required for male sex determination.

Concentration of serum testosterone in XY sex reversed horses.

The XY Sex Reversal Syndrome of the horse is a condition associated with female or intersexual development in genetic males. In our previous study, 38 sex reversed XY mares were classified according to behavior, gross clinical phenotype, gonadal status, and H-Y phenotype. Four classes were described, ranging from potentially fertile female (Class I) to virilized intersex (Class IV). In the present study, serum testosterone concentrations were measured in 29 sex-reversed XY mares, 3 normal mares and 3 normal stallions. Serums were obtained during the breeding season (March-August), and were stored at -70 C until assayed. Serum testosterone concentrations in the normal XX mares ranged from nondetectable to 0.41 ng/ml; in normal XY stallions, from 1.04 ng/ml to 2.4 ng/ml; and in XY mares, from nondetectable to 5.4 ng/ml. Sex reversed mares previously assigned to Class I or II had serum testosterone concentrations ranging from nondetectable to 0.22 ng/ml. Serum testosterone concentrations in XY mares were correlated with sex phenotype and behavior. Although the range of steroid concentrations among XY mares may be quantified more accurately with increased sampling, serum testosterone concentrations can be used currently as an added parameter for study of the sex reversed condition.

XY sex reversal syndrome in the mare: clinical and behavioral studies, H-Y phenotype.

An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; class III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and class II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive.

Genetics of XY sex reversal in the mouse: [formula omitted][formula omitted]. Unités des Génétique des Mammifères et Immunogénétique Humaine, Institut Pasteur, Paris, France

Genetics of XY sex reversal in the mouse: [formula omitted][formula omitted]. Unités des Génétique des Mammifères et Immunogénétique Humaine, Institut Pasteur, Paris, France

Morphological development of the mouse gonad in tda-1 XY sex reversal

tda-1 XY sex reversal occurs when the Y chromosome of at least some populations of wild Mus musculus domesticus is placed on the C57BL/6J genomic background. Gross anatomical observations have previously revealed morphological similarities among fetal ovotestes of tab-1 and Tus-inherited XY sex reversals and BALB/cWt mosaic hermaphrodites. We studied the histology of tda-1 XY sex-reversed gonads, ranging in age from day 14 of gestation to adult. The obtained data revealed additional similarities with ovotestes of BALB/cWt mosaic hermaphrodites as well as with ovotestes of hermaphrodites found in XX sxr and XX/XY chimeras. It is proposed that ovotestes occurring in these various hermaphroditic conditions may be formed through a common pathway.

Studies on the genetics of tda-1 XY sex reversal in the mouse

When the Y chromosome of at least some populations of the house mouse of Western Europe and the Mediterranean, Mus musculus domesticus. is placed into the C57BL/6J (B6) inbred mouse genome, XY fetuses develop into hermaphrodites or females. It has been hypothesized that the testis-determining gene on the Y chromosome of M. m. domesticus ( Tdy DOM ) interacts improperly with a putative B6/J recessive, testisdetermining, autosomal gene ( tdu-1). The present study extended these earlier findings. The mating of B6 mice possessing the Y chromosome of M. m. domesticus (B6.Y DOM/Na; N6-N9) to females of the AKR, BALB/c, C3H/An. and C3H/He, but not SJL, strains resulted in aberrant testicular differentiation in day-14/ 15 F1 fetuses. The aberrant testes were characterized by a delay in testicular differentiation at the cranial and caudal poles of the gonad, i.e., the presence of a thin (or no) tunica albuginea and the presence of disorganized (or no) seminiferous tubules. Crossing B6.Y DOM male phenotypes with SJL females did not result in aberrant testicular differentiation, suggesting that the SJL strain possesses the dominant testis-determining, autosomal-1 allele, Tda-1. Studies using re-combinant DNA probes specific for the murine Y chromosome have suggested that the SJL and AKR strains possess the M. m. domesticur Y chromosome. When the Y chromosomes of the SJL and AKR strains were placed on the B6 background, aberrant testicular differentiation similar to tda-1 XY sex reversal occurred in only 1 out of 87 (1%) N4 day-14/15 fetuses possessing Y AKR, but in 25 out of 45 (56%) N4 day-14/15 fetuses possessing Y AKR. In fetuses possessing Y AKR, the affected testes recovered during further fetal development, since overt hermaphroditism was not seen postnatally, i.e., neither at the anatomical nor histological levels. We conclude that although SJL, AKR, and wild M. m. domesticus possess an identical Y chromosome restriction fragment-length polymorphism, they possess either different alleles of the testis-determining gene, Tdy, or other genes modifying testicular differentiation.

Histochemistry of Liver Tumors Induced by Diethylnitrosamine and Differential Sex Susceptibility to Carcinogenesis in <italic>Oryzias latipes</italic>

Liver tumor nodules were induced by the administration of diethylnitrosamine [(DENA) CAS: 55-18-5; N-nitrosodiethylamine] to the fish, Oryzias latipes. A histochemical study showed decreased ATPase and glucose 6-phosphatase (Glc-6-Pase) activities in most of the tumor nodules. Increased ATPase staining and, occasionally, Glc-6-Pase staining were also observed. In some nodules, the distribution of bile canaliculi was disordered, indicating positive ATPase activity. Basophilic and eosinophilic nodules could be discriminated by histologic examination. The observations on serial histochemical and histologic sections revealed extreme heterogeneity in the phenotypes of the nodules. Measurement of the enzyme-altered areas indicated that the development of nodules was more prominent in male than in female fish. Experiments with sex-reversed fish, XX males and XY females, suggested that the sex difference in the susceptibility to DENA does not result from the difference in sex chromosomes but from the difference in sexual phenotypes.