A duplicated copy of DMRT1 in the sex-determining region of the Y chromosome of the medaka,Oryzias latipes

The genes that determine the development of the male or female sex are known in Caenorhabditis elegans, Drosophila, and most mammals. In many other organisms the existence of sex-determining factors has been shown by genetic evidence but the genes are unknown. We have found that in the fish medaka the Y chromosome-specific region spans only about 280 kb. It contains a duplicated copy of the autosomal DMRT1 gene, named DMRT1Y. This is the only functional gene in this chromosome segment and maps precisely to the male sex-determining locus. The gene is expressed during male embryonic and larval development and in the Sertoli cells of the adult testes. These features make DMRT1Y a candidate for the medaka male sex-determining gene.     

46,XX Male Disorder of Sexual Development: A Case Report

The main factor influencing sex determination of an embryo is the sex-determining region Y (SRY), a master regulatory gene located on the Y chromosome. The presence of SRY causes the bipotential gonad to differentiate into a testis. However, some individuals carry a Y chromosome but are phenotypically female (46,XY females) or have a female karyotype but are phenotypically male (46,XX males). 46, XX male is rare (1:20 000 in newborn males), and SRY positivity is responsible for this condition in approximately 90% of these subjects. External genitalia of 46,XX SRY-positive males appear as normal male external genitalia, and such cases are diagnosed when they present with small testes and/or infertility after puberty. Herein, we report an adolescent who presented with low testicular volume and who was diagnosed as a 46,XX male. SRY positivity was demonstrated in the patient by fluorescence in situ hybridization method. Conflict of interest:None declared.     

A W-linked DM-domain gene, DM-W, participates in primary ovary development in Xenopus laevis

In the XX/XY sex-determining system, the Y-linked SRY genes of most mammals and the DMY/Dmrt1bY genes of the teleost fish medaka have been characterized as sex-determining genes that trigger formation of the testis. However, the molecular mechanism of the ZZ/ZW-type system in vertebrates, including the clawed frog Xenopus laevis, is unknown. Here, we isolated an X. laevis female genome-specific DM-domain gene, DM-W, and obtained molecular evidence of a W-chromosome in this species. The DNA-binding domain of DM-W showed a strikingly high identity (89%) with that of DMRT1, but it had no significant sequence similarity with the transactivation domain of DMRT1. In nonmammalian vertebrates, DMRT1 expression is connected to testis formation. We found DMRT1 or DM-W to be expressed exclusively in the primordial gonads of both ZZ and ZW or ZW tadpoles, respectively. Although DMRT1 showed continued expression after sex determination, DM-W was expressed transiently during sex determination. Interestingly, DM-W mRNA was more abundant than DMRT1 mRNA in the primordial gonads of ZW tadpoles early in sex determination. To assess the role of DM-W, we produced transgenic tadpoles carrying a DM-W expression vector driven by approximately 3 kb of the 5'-flanking sequence of DM-W or by the cytomegalovirus promoter. Importantly, some developing gonads of ZZ transgenic tadpoles showed ovarian cavities and primary oocytes with both drivers, suggesting that DM-W is crucial for primary ovary formation. Taken together, these results suggest that DM-W is a likely sex (ovary)-determining gene in X. laevis.     

An SRY-related sequence on the marsupial X chromosome: implications for the evolution of the mammalian testis-determining gene.

The SRY gene on the human, mouse, and marsupial Ychromosomes is the testis-determining gene that initiates male development inmammals. The SRY protein has a DNA-binding domain (high mobility group or HMGbox) similar to those found in the high-mobility-group proteins. SRY is specificfor the Y chromosome, but many autosomal genes have been identified that possessa similar HMG box region; those with the most closely SRY-related box regionsform a gene family now referred to as SOX genes. We have identified a sequenceon the marsupial X chromosome that shares homology with SRY. Sequencecomparisons show near-identity with the mouse and human SOX3 gene (formerlycalled a3), the SOX gene which is the most closely related to SRY. We suggesthere that the highly conserved X chromosome-linked SOX3 represents the ancestralSOX gene from which the sex-determining gene SRY was derived. In this modelSOX3/SRY divergence and the acquisition of a testis-determining role by SRYmight have preceded (and initiated) sex chromosome differentiation or,alternatively, might have been a consequence of X chromosome-Y chromosomedifferentiation initiated at the locus of an original sex-determining gene(s),later superseded by SRY.     

Screening for Y-derived sex determining gene SRY in 40 patients with Turner syndrome.

In Turner patients, the presence of a Y chromosome or derivative Y is correlated with the risk of gonadoblastoma induction. "Marker" chromosomes originating from Y, may not show characteristic fluorescence and then be very difficult to identify by conventional cytogenetic techniques, although they still predispose the patients to gonadal tumors. Using polymerase chain reaction of the gene from the sex-determining region of the Y chromosome, we screened 40 Turner patients (thirty seven 45X and three 45X,46XX) for the presence of Y chromosomal DNA. We were able to identify karyotypically unrecognized Y chromosome material in 1 patient out of the 40 studied. In this patient mild clinical and biological hyperandrogenism was observed. Reliability of our technique was ascertained by the detection of the expected 648 base pairs amplified DNA fragment in all normal male controls as well as in 3 Turner patients with confirmed 45X,46XY mosaicism. Despite the low frequency of unrecognized Y chromosome material (1 case over 40 in our experience), our data suggest that polymerase chain reaction of the gene from the sex-determining region of the Y chromosome is worthy of being performed in Turner patients considering the potential risk of the presence of a Y chromosome.     

Regulation of the phenotype of ovarian somatic cells by estrogen

The pathway of mammalian sex determination, and subsequent differentiation of the gonads is under the control of the sex-determining gene, Sry, on the Y chromosome. The presence of Sry leads to the formation of a testis with its complement of Sertoli and Leydig somatic cells. In the absence of Sry, an ovary develops with granulosa and theca cells. Ovarian development is said to initiate in the XX gonad as a default pathway because the XX cells do not express Sry. This review summarizes evidence supporting the view that the ovary is not entirely a default gonad. Studies of mice with deletions in both estrogen receptor (ERalphabetaKO) or aromatase (ArKO) genes have identified an important role of estrogens in maintaining differentiation and development of somatic cells in the ovary of eutherian mammals. In the absence of estrogen (ArKO) or the capacity to transduce an estrogen signal (ERalphabetaKO), the somatic cells in the ovary exhibited a male phenotype including Sertoli and Leydig cells. When ArKO mice were replaced with estrogen, the male phenotype was diminished and there was evidence of normal folliculogenesis in the ovary. It is concluded that the differentiation of somatic cells in the eutherian ovary is influenced by the sex steroid environment.     

Normal female phenotype and ovarian development despite the ovarian expression of the sex-determining region of Y chromosome (SRY) in a 46,XX/69,XXY diploid/triploid mosaic child conceived after in vitro fertilization-intracytoplasmic sperm injection

CONTEXT: Diploid/triploid mosaicism (mixoploidy) is a rare chromosomal abnormality characterized by mental and growth retardation, hypotonia, and dysmorphic features such as facial asymmetry, low-set ears, and syndactyly. All 46,XX/69,XXY cases fall into three phenotypic groups: male with testicular development, ovotestis disorder of sex development (DSD), or undervirilized male DSD. All phenotypic females with diploid/triploid mosaic reported so far had 46,XX/69,XXX karyotype. PATIENT: We report an 8-year-old girl conceived after in vitro fertilization-intracytoplasmic sperm injection with normal internal/external genital and ovarian development despite 46,XX/69,XXY mosaicism and normal expression of sex-determining region of Y chromosome (SRY) in her gonads. INTERVENTION: Because of the increased risk of gonadoblastoma resulting from Y chromosome mosaicism, her ovaries were removed by laparoscopy. Ovarian tissue was analyzed histologically as well as by fluorescence in situ hybridization, PCR, and RT-PCR amplification to determine the localization of Y chromosome and expression of SRY and DAX1 mRNA. Methylation-specific PCR was used to assess the inactivation pattern of X chromosomes. RESULTS: By laparoscopy, internal female genital anatomy appeared to be normal. Cytogenetic and molecular methods confirmed the presence of intact and functionally active Y chromosome in the ovary. Strikingly, histological assessment of the gonads showed normal ovarian architecture with abundant primordial follicles despite the presence of the Y chromosome in ovarian follicles and the expression of SRY mRNA in gonadal tissue. CONCLUSION: This case illustrates that normal ovarian development is possible in the presence of Y chromosome in ovarian follicles and despite the expression of SRY in ovarian tissue. Furthermore, this is the first documented case of mixoploidy after in vitro fertilization-intracytoplasmic sperm injection and the only phenotypic female with 46,XX/69,XXY karyotype.     

The human sex-reversing ATRX gene has a homologue on the marsupial Y chromosome, ATRY: implications for the evolution of mammalian sex determination

Mutations in the ATRX gene on the human X chromosome cause X-linked alpha-thalassemia and mental retardation. XY patients with deletions or mutations in this gene display varying degrees of sex reversal, implicating ATRX in the development of the human testis. To explore further the role of ATRX in mammalian sex differentiation, the homologous gene was cloned and characterized in a marsupial. Surprisingly, active homologues of ATRX were detected on the marsupial Y as well as the X chromosome. The Y-borne copy (ATRY) displays testis-specific expression. This, as well as the sex reversal of ATRX patients, suggests that ATRY is involved in testis development in marsupials and may represent an ancestral testis-determining mechanism that predated the evolution of SRY as the primary mammalian male sex-determining gene. There is no evidence for a Y-borne ATRX homologue in mouse or human, implying that this gene has been lost in eutherians and its role supplanted by the evolution of SRY from SOX3 as the dominant determiner of male differentiation.     

Y is there a risk to being male?

Being male or female can make a vital difference to many important biological functions and can lead to disparities in health. The Y chromosome carries the sex-determining sex reversal Y (SRY) gene and recent studies show that it might also harbor genes that have important biological functions other than sex determination. One such example is the emerging evidence from animal models and humans that supports the presence of cardiovascular genes on the Y chromosome. A significant amount of work remains to identify these genes; however, we report here observations linking the Y chromosome to hypertension, which could explain the higher incidence of cardiovascular disease in males compared with females.     

Identification and characterization of an Xp22.33;Yp11.2 translocation causing a triplication of several genes of the pseudoautosomal region 1 in an XX male patient with severe systemic lupus erythematosus

The X;Y translocation break point sequence in an XX male patient with prepubertal systemic lupus erythematosus (SLE) was characterized with the intention of identifying a predisposing gene(s) for SLE. Spectral karyotyping of the patient's metaphase chromosomes showed normal autosomes and 2 X chromosomes, one of which displayed a small portion of the Y chromosome. Using a Y chromosome polymerase chain reaction (PCR) walking strategy and inverse PCR, we found that the abnormal recombination occurred between retroviral long terminal repeats located at Xp22.33 (position 0.95 Mb; inside the pseudoautosomal regions) and Yp11.2 (4.20 Mb) downstream of the sex-determining region Y (SRY) gene. The complete DNA sequence of the break point was determined, revealing a partial duplication of the pseudoautosomal region 1 (PAR1) in the derivative X chromosome and causing a partial trisomy of the 12 known genes located between the interleukin-3 receptor alpha (IL3RA; position 1.1 Mb on the X and Y chromosomes) and CD99 (position 2.2 Mb) genes inclusively. All other X chromosome genes were present as 2 copies. Real-time quantitative PCR confirmed the presence of 3 copies of each of the 12 genes in the patient's genomic DNA. We also found that RNA for 1 of the candidate genes was indeed overexpressed in the patient's blood as compared with normal subjects. Taken together, the uniqueness of the translocation, the rarity of severe prepubertal SLE in males, and the presence of SLE in some patients with Klinefelter's syndrome (who have a triplication of the 2 PAR regions) point to a possible relationship between the partial triplication of the PAR1 region and the development of SLE.     

A de novo phe671eu mutation in the SRY gene in a patient with complete 46,XY gonadal dysgenesis

The sex-determining region of the Y chromosome (SRY) gene initiates the process of male sex differentiation in mammalians. In humans, mutations in the SRY gene have been reported to account for 10-15% of the XY sex reversal cases. In this report we describe the clinical, endocrinological and molecular data of a patient with complete 46,XY gonadal dysgenesis caused by a de novo mutation affecting SRY amino acid phenylalanine at position 67 (F67L), located within the highly conserved high mobility group (HMG) box coding region of the gene.     

Location of the genes controlling H-Y antigen expression and testis determination on the mouse Y chromosome.

Sex-reversed XX male mice that carry the variant form of the testis-determining Sxr region, Sxr', do not express male-specific H-Y antigen. In a stock of mice segregating for Sxr', we detected an exceptional XX male that proved positive for H-Y antigen. DNA fingerprinting revealed that the banding pattern characteristic of Sxr' had been replaced by the pattern associated with the native testis-determining region of the normal Y chromosome of that stock, presumably by pairing and crossing-over between the two testis-determining regions of the father's Y Sxr' chromosome. Pairing between the two ends of such a chromosome in a loop-like configuration has been observed by electron microscopy. However, an anomalous crossing-over event of this kind would only give rise to the observed result if the native homologue of the Sxr region were situated on the very minute short arm of the Y chromosome. We therefore conclude that the two linked genes Tdy and Hya, controlling testis determination and H-Y antigen expression, respectively, are located on the short arm of the mouse Y chromosome.     

Exchange of terminal portions of X- and Y-chromosomal short arms in human XY females.

Human Y(+) XX maleness has been shown to result from an abnormal terminal Xp-Yp interchange that can occur during paternal meiosis. To test whether human XY females are produced by the same mechanism, we followed the inheritance of paternal pseudoautosomal loci and Xp22.3-specific loci in two XY female patients. Y-specific sequences and the whole pseudoautosomal region of the Y chromosome of their fathers were absent in these patients. However, the entire pseudoautosomal region and the X-specific part of Xp22.3 distal to the STS locus had been inherited from the X chromosome of the respective father. This Xp transfer to Yp was established by in situ hybridization experiments showing an Xp22.3-specific locus on Yp in both cases. Such results demonstrate that an abnormal and terminal X-Y interchange generated the rearranged Y chromosome of these two XY females; they appear to be the true countertype of Y(+) XX males. In these patients, who also display some Turner stigmata, the Y gene(s) involved in this phenotype is (are) localized to interval 1 or 2. If the loss of such gene(s) affects fetal viability, their proximity to TDF would account for the underrepresentation of interchange 46,XY females compared with Y(+) XX males.     

Analysis of the sex-determining region of the Y chromosome (SRY) in sex reversed patients: point-mutation in SRY causing sex-reversion in a 46,XY female.

The first and essential step in normal sexual differentiation takes place during the 5th-6th week of gestation. The testis determining factor (TDF) directs the undifferentiated gonad into a testis, which secretes hormones responsible for normal male development. A new candidate for TDF has recently been reported, and it has been called the sex determining region of the Y (SRY). The hypothesis has been supported by the finding of XX individuals with SRY, and two females with 46,XY karyotype and a mutation in SRY. However, XX males without SRY has been reported, and the role of SRY still has to be determined. We have tested three human females with 46,XY karyotype and gonadal dysgenesis and two 46,XX males for the presence of SRY using the polymerase chain reaction and subsequent DNA sequencing. Both 46,XX males contained SRY, whereas one of the 46,XY females had suffered a point mutation in SRY changing a codon for lysine to a stop codon. This information supports the hypothesis that SRY is significant in normal male sex differentiation. The two remaining 46,XY individuals had an intact HMG box, but it is possible that a mutation may be found in a regulatory gene or further downstream in the gene regulatory cascade. Two patients including the one with a mutation in SRY had gonadoblastomas supporting the hypothesis that another gene on the Y-chromosome is involved in the pathogenesis of this neoplasia.     

Clinical and anatomical spectrum in XX sex reversed patients. Relationship to the presence of Y specific DNA-sequences

OBJECTIVE Testicular differentiation can occur in the absence of the Y chromosome giving XX sex-reversed males. Although Y chromosomal sequences can be detected in the majority of male subjects with a 46,XX karyotype, several studies have shown that approximately 10% of patients lack Y material including the SRY gene. The aim of this study was to see if the classification of XX sex-reversed individuals into three groups, Y-DNA-positive phenotypically normal XX males, Y-DNA-negative XX males with genital ambiguities and Y-DNA-negative true hermaphrodites can be applied to our cases. DESIGN Endocrinological and genetic studies were conducted in 20 XX sex-reversed patients. PATIENTS Twenty patients with various phenotypes were studied. They were between 20 days and 35 years old. Ten presented ambiguous external genitalia (Prader's stages II to IV). After laparotomy or gonadal biopsy, the diagnosis was 46, XX true hermaphroditism in five, and XX male in 15. MEASUREMENTS Blood samples were obtained from all patients for hormonal and molecular studies. Basal levels of testosterone, oestradiol and pituitary gonadotrophins were measured by RIA, In addition, two stimulation tests were performed: gonadotrophin stimulation with GnRH and testicular stimulation with hCG. Several Y-specific DNA sequences of the short arm of the Y chromosome were analysed by Southern blot and polymerase chain reaction methods. RESULTS In this study, three categories of XX sex-reversed individuals were observed: phenotypically normal males with or without gynaecomastia, males with genital ambiguities, and true hermaphrodites. Endocrinological data were similar in XX males and in true hermaphrodites. Testosterone levels exhibited normal (n= 9) or decreased (n= 11) values. The hCG response was low. FSH and LH were elevated in 13 patients. Molecular analysis in ten patients showed varying amounts of Y material including the Y boundary and SRY. Ten patients with various phenotypes lacked Y chromosomal DNA. There was no relation between Leydig cell function (as indicated by testosterone levels before or after hCG stimulation) and the presence of Y chromosome material. CONCLUSION Although the presence of Y-specific DNA generally results in a more masculinized phenotype, exceptions do occur. In the Y-DNA-negative group, complete or incomplete masculinization in the absence of SRY suggests a mutation of one or more downstream non-Y, testis-determining genes.     

An analysis of the genetic factors involved in testicular descent in a cohort of 14 male patients with anorchia

Anorchia, or the "vanishing testis syndrome," is characterized by the absence of testis in a 46,XY individual with a male phenotype. The etiology is unknown; however, the familial occurrence of the disease and the association of this phenotype with 46,XY gonadal dysgenesis has led to the suggestion that genetic factors, which play a role in testicular determination, may be involved. Alternatively, exploratory laparoscopy has suggested that anorchia may be caused by a prenatal testicular vascular accident associated with torsion during testicular descent. We screened a cohort of 14 boys with bilateral anorchia for mutations in the Y chromosome-linked testis-determining gene SRY (sex-determining region, Y chromosome); in the gene necessary for correct testicular descent, INSL3; and in the gene of its receptor (LGR8). Mutations in the INSL3 gene and the LGR8 T222P mutation are known to cause cryptorchidism. We confirmed previous reports that mutations in the SRY gene are not associated with anorchia. Although a common polymorphism was identified in the INSL3 gene, no mutations were observed. The recurrent T222P mutation in the LGR8 gene was not found in any of the patients. These data show for the first time a lack of association between genetic factors necessary for correct testicular descent and anorchia.