The sex-determining region of the human Y chromosome encodes a finger protein

Reliable sex identification of dogs by modified PCR/RFLP analysis

To find definitive RFLP sites for canine sex determination, DNA segments corresponding to parts of the canine ZFX and ZFY genes were amplified by PCR and were directly sequenced. According to the newly defined sequence data, the combination of Haelll and Cfr13I sites was found to be useful for not only identifying the sex of the canine DNA samples but also distinguishing them from the human DNA. Conveniently, these two enzymes worked simultaneously in the same single buffer. The double-digestion of the ZFX/ZFY PCR products with HaeIII and Cfr13I showed banding patterns unique to males and females in Canis familialis. This PCR/RFLP method was confirmed to be applicable to various breeds of dog.

The human Y chromosome derives largely from a single autosomal region added to the sex chromosomes 80-130 million years ago

Mapping of human X-borne genes in distantly related mammals has defined a conserved region shared by the X chromosome in all three extant mammalian groups, plus a region that was recently added to the eutherian X but is still autosomal in marsupials and monotremes. Using comparative mapping of human Y-borne genes, we now directly show that the eutherian Y is also composed of a conserved and an added region which contains most of the ubiquitously expressed Y-borne genes. Little of the ancient conserved region remains, and the human Y chromosome is largely derived from the added region.

The human Y chromosome: function, evolution and disease

The human Y chromosome is strictly paternally inherited and, in most of its length, does not recombine during male meiosis. These features make the Y a very useful genetic marker for different purposes. In the last decade, the Y has been increasingly used to investigate the evolution, migrations and range expansions of modern humans. The possibility to construct highly informative Y chromosome haplotypes has also had a significant impact in forensic studies and paternity testing. All these studies assume that the Y chromosome markers used are selectively neutral. However, recent experimental and statistical analyses suggest that both positive and negative selection are acting on the Y chromosome and, consequently, may influence Y chromosome haplotype distribution in the general population. Current data suggest that the effects of selection on patterns of Y chromosome distribution are minimal, however as interest focuses on biological functions of the Y chromosome which have a major impact on male fitness such as fertility, these assumptions may be challenged. This review briefly describes the genes and biological functions of the human Y chromosome and its use in disentangling the origin and history of human populations. An overview of the role of selection acting on the Y chromosome from the perspective of human population histories and disease is given.

Sex chromosomes, sex-linked genes, and sex determination in the vertebrate class amphibia

In this chapter the different categories of homomorphic and heteromorphic sex chromosomes, types of sex-determining mechanisms, known sex-linked genes, and data about sex-determining genes in the Amphibia have been compiled. Thorough cytogenetic analyses have shown that both XY/XX and ZW/ZZ sex chromosomes exist in the order Anura and Urodela. In some species quite unusual systems of sex determination have evolved (e.g. 0W-females/00-males or the co-existence of XY/XX and ZW/ZZ sex chromosomes within the same species). In the third order of the Amphibia, the Gymnophiona (or Apoda) there is still no information regarding any aspect of sex determination. Whereas most species of Anura and Urodela present undifferentiated, homomorphic sex chromosomes, there is also a considerable number of species in which an increasing structural complexity of the Y and W chromosomes exists. In various cases, the morphological differentiation of the sex chromosomes occurred as a result of quantitative and/or qualitative changes to the repetitive DNA sequences in the constitutive heterochromatin of the Y and W chromosomes. The greater the structural differences between the sex chromosomes, the lesser the extent of pairing in meiosis. No dosage compensation of the sex-linked genes in the somatic cells of the homogametic (XX or ZZ) individuals have been detected. The genes located to date on the amphibian sex chromosomes lead to the conclusion that there is no common ancestral or conserved sex-linkage group. In all amphibians, genetic sex determination (GSD) seems to operate, although environmental factors may influence sex determination and differentiation. Despite the accumulated evidence that GSD is operating in Anura and Urodela, there is little substantial information about how it functions. Although several DNA sequences homologous to the mammalian ZFY, SRY and SOX genes have been detected in the Anura or Urodela, none of these genes is an appropriate candidate to explain sex determination in these vertebrates.

Sex chromosomes and sex-determining genes: insights from marsupials and monotremes

Comparative studies of the genes involved in sex determination in the three extant classes of mammals, and other vertebrates, has allowed us to identify genes that are highly conserved in vertebrate sex determination and those that have recently evolved roles in one lineage. Analysis of the conservation and function of candidate sex determining genes in marsupials and monotremes has been crucial to our understanding of their function and positioning in a conserved mammalian sex-determining pathway, as well as their evolution. Here we review comparisons between genes in the sex-determining pathway in different vertebrates, and ask how these comparisons affect our views on the role of each gene in vertebrate sex determination.

Three thousand years of questioning sex determination

Of all the inborn differences that distinguish individual humans, as well as other animals, sex exerts the most far-reaching effects, and the question, what determines it, has been debated throughout history. A discriminating reading of Biblical and Ancient Greek sources reveals surprising insights that are relevant to present-day biology. The material basis of generation was inaccessible until, following the invention of the microscope and the discovery of "spermatic animalcules" in the 17th century, the 19th century witnessed the discovery of the mammalian egg, the nature of sperm, and the process of fertilization. Sex was thought to be determined by external conditions. The 20th century developed the genetics of sex determination. The search for the mammalian testis-determining gene during the last quarter century culminated in the discovery of SRY, soon to be accompanied by non-Y chromosome sex- determining genes. During the same period, data accumulated that testicular differentiation was accompanied by accelerated gonadal growth; subsequently, differences in growth were shown to distinguish early XX from early XY embryos. Other research showed that temperature-dependent sex determination was widely distributed among reptiles, thus illustrating that the mammalian system of sex determination is of recent evolutionary origin, adopted in response to homoiothermy and placentation. The recent discovery that Sry induces cell proliferation in the gonads of fetal mice suggests that the task for the 21st century will be to aim beyond simple genotype/phenotype correlations by unraveling the relationship between genes and epigenetic factors acting on cell growth during development and affecting the phenotype in later life.

The minimal mammalian Y chromosome - the marsupial Y as a model system

The mammalian X and Y chromosomes are very different in size and gene content. The Y chromosome is much smaller than the X and consists largely of highly repeated non-coding DNA, containing few active genes. The 65-Mb human Y is homologous to the X over two small pseudoautosomal regions which together contain 13 active genes. The heterochromatic distal half of the human Yq is entirely composed of highly repeated non-coding DNA, and even the euchromatic portion of the differential region is largely composed of non-coding repeated sequences, amongst which about 30 active genes are located. The basic marsupial Y chromosome (about 10 Mb) is much smaller than that of humans or other eutherian mammals. It appears to include no PAR, since it does not undergo homologous pairing, synaptonemal complex formation or recombination with the X. We show here that the tiny dunnart Y chromosome does not share cytogenetically detectable sequences with any other chromosome, suggesting that it contains many fewer repetitive DNA sequences than the human or mouse Y chromosomes. However, it shares several genes with the human and/or mouse Y chromosome, including the sex determining gene SRY and the candidate spermatogenesis gene RBMY, implying that the marsupial and eutherian Y are monophyletic. This minimal mammalian Y chromosome might provide a good model Y in which to hunt for new mammalian Y specific genes.

XX males without SRY gene and with infertility

The case of a 28 year old male with normal male phenotype, in whom repeated seminal analysis showed complete azoospermia, is presented. Peripheral blood culture for chromosome studies revealed 46 chromosomes with XX constitution. Polymerase chain reaction (PCR) analysis of genomic DNA failed to detect the presence of the sex-determining region of the Y chromosome (SRY). A literature review of all SRY-negative XX males with normal male phenotype showed that this case is the sixth reported case but the first to be diagnosed during the investigations of infertility. The frequency, aetiology and diagnosis of this rare syndrome are also reviewed.

[Rapid determination of sex in Myocastor coypus embryos in the first stage of gestation]

The early knowledge of the sex may be crucial for the understanding of many features of ecological and evolutive biology, including offspring sex-ratio adjustment and evolution of breeding systems. In coypu (Myocastor coypus), significant variation in birth sex-ratios can be observed and selective abortion of entire litters is one of the cited mechanisms. In order to determine the sex of coypu embryos in the earlier stages of gestation (second week), we developed a molecular technique based on PCR amplification of a region of the Sry gene. These method used the combination of two sets of primers: one specific of the Y-chromosome; the other one, autosomal, is a positive control for amplification. Because of the direct amplification of embryo lysate without DNA extraction, the present sexing technique is rapid, relatively simple and inexpensive, and presents numerous advantages for the study at population scale.

Surgical treatment of congenital adrenal hyperplasia

Unraveling of the genetics of CAH offers the possibility of earlier detection and prenatal treatment or, alternatively, blastocyst embryo selection and eventually in utero gene therapy. Endocrine, surgical, and anesthesia management after birth have improved, leading to a better outcome for these patients. In the authors' experience, early one-stage reconstructive surgery, although demanding, allows one to use all available tissue. Once mastered, the repair is actually technically easier than vaginal pull-through surgery in the adolescent. Patients go through childhood with a body image that is more concordant with normal. Neither the child nor the parents must suffer the anticipation of a major operative intervention at puberty that can cause great emotional stress and that may be more difficult. The authors have encountered situations in late adolescence in which it has been impossible to separate the urogenital sinus from below. Under these circumstances, one can consider a posterior sagittal approach in which the rectum is bivalved to allow one to approach the vagina from below in an attempt to separate it safely from the urethra and to mobilize it to the perineum. It is also feasible to consider fashioning a segment of sigmoid colon as a neovagina, realizing that mucosal drainage needs to be managed daily. The authors have also encountered the rare 46,XX patient raised as a male and committed to the male role. In these cases, the patient can be offered gonadectomy, followed by staged complex hypospadias repair, and surgery to remove Müllerian structures and, if possible, to preserve the vas, followed by prepenile scrotal repair and insertion of testicular prostheses. Children with CAH require a lifetime of care with surgical approaches that are age appropriate. These patients can lead a full and productive life. It is the physician's responsibility to make certain that these children reach their full potential with the least number of interventions, which should be designed and optimized to produce the best possible outcome.

DNA recognition by Cys2His2 zinc finger proteins

Cys2His2 zinc fingers are one of the most common DNA-binding motifs found in eukaryotic transcription factors. These proteins typically contain several fingers that make tandem contacts along the DNA. Each finger has a conserved beta beta alpha structure, and amino acids on the surface of the alpha-helix contact bases in the major groove. This simple, modular structure of zinc finger proteins, and the wide variety of DNA sequences they can recognize, make them an attractive framework for attempts to design novel DNA-binding proteins. Several studies have selected fingers with new specificities, and there clearly are recurring patterns in the observed side chain-base interactions. However, the structural details of recognition are intricate enough that there are no general rules (a "recognition code") that would allow the design of an optimal protein for any desired target site. Construction of multifinger proteins is also complicated by interactions between neighboring fingers and the effect of the intervening linker. This review analyzes DNA recognition by Cys2His2 zinc fingers and summarizes progress in generating proteins with novel specificities from fingers selected by phage display.

Glucose and pyruvate metabolism during mouse gonadal sex differentiation

In the mouse, gonadal sex differentiation starts around E12 and meiosis begins in the ovary shortly after E13. In the search for metabolic changes that might be correlated to gonadal sex differentiation and/or possibly the onset of meiosis, we investigated the metabolism of glucose and pyruvate in the developing mouse ovary before (E11.5-E12.5), during (E14.5-16.5), and after meiosis (E18.5), and in fetal testes without meiosis. Gonads were cultured with 14C-labeled glucose (0.02 and 5.58 mM) and 14C-pyruvate (0.17 mM). The oxidation expressed as 14CO2 production and the organification expressed as retention of 14C in the tissues were measured and correlated to the protein content of the gonads. Using 0.02 mM glucose, a decline in oxidation and organification was found in ovaries as well as in testes, which is probably related to starvation. Using 5.58 mM glucose, a continuous decline in oxidation was seen only in the testis. Organification of 0.17 mM pyruvate increased at E12.5 and E14.5 in the ovary but not in the testis. This was in despite of an exponential increase of protein content in the testes compared to only a moderate increase in the ovary. The CO2 production from 5.58 mM glucose was equal to that from 0.17 mM pyruvate in gonads of both sexes. In conclusion, an increased metabolism of 5.58 mM glucose and 0.17 mM pyruvate in the ovaries as compared to the testes is related to sex differences during gonadal formation and onset of meiosis in the ovaries. J. Exp. Zool. 288:130-138, 2001.

The Human Y Chromosome: The Biological Role of a "Functional Wasteland"

"Functional wasteland," "Nonrecombining desert" and "Gene-poor chromosome" are only some examples of the different definitions given to the Y chromosome in the last decade. In comparison to the other chromosomes, the Y is poor in genes, being more than 50% of its sequence composed of repeated elements. Moreover, the Y genes are in continuous decay probably due to the lack of recombination of this chromosome. But the human Y chromosome, at the same time, plays a central role in human biology. The presence or absence of this chromosome determines gonadal sex. Thus, mammalian embryos with a Y chromosome develop testes, while those without it develop ovaries (Polani, 1981). What is responsible for the male phenotype is the testis-determining SRY gene (Sinclair, 1990) which remains the most distinguishing characteristic of this chromosome. In addition to SRY, the presence of other genes with important functions has been reported, including a region associated to Turner estigmata, a gene related to the development of gonadoblastoma and, most important, genes related to germ cell development and maintenance and then, related with male fertility (Lahn and Page, 1997). This paper reviews the structure and the biological functions of this peculiar chromosome.

A zinc finger domain gene in the lizard, Calotes versicolor, shows extensive homology with the mammalian ZFX and is expressed embryonically

A 590-bp long zinc finger domain DNA fragment has been isolated by polymerase chain reaction from the lizard, Calotes versicolor, employing the primers used for amplifying the zinc finger domain of the human Y-chromosomal gene, ZFY. Cloned in pUC18, the fragment, called CvZfa, was sequenced and its expression during development was studied. At the nucleotide and amino acid level CvZfa shows respectively 83% and 90% identity with the human ZFY, but its extent of homology is greater with the ZFX of human (86% at nucleotide and 92% at amino acid level) and the ZFY-like genes of turtle and chick. Similarly its homology with the mouse Zfx and Zfa is much greater than that with Zfy-1 and Zfy-2. It appears that the mammalian ZFX (Zfx) evolved from reptilian ancestors with a considerable degree of conservation, but the ZFX to ZFY divergence within the class mammalia was more rapid. The CvZfa transcripts were seen in all the embryonic stages from which RNA was analysed. The whole mount in situ hybridization with the posteriorly placed mesonephros and the gonadal primordia of 10 to 25 day old embryos showed signal selectively in mesonephros of the 20 and 25 day embryos. There was no signal in the genital ridge. Thus CvZfa may not have a direct role in gonadogenesis of C. versicolor, but the possibility of its inductive role in the formation of adreno-gonadal axis through mesonephros cannot be discounted.

Sex determination in Ellobius lutescens: the story of an enigma

The unusual karyotype of Ellobius lutescens (2n = 17,X in males and females) has attracted permanent interest and prompted a series of hypotheses on sex determination in this species since its first description by Matthey (1953). The developing knowledge about the sex chromosomes and sex determination as well as the availability of new cytogenetic and molecular genetic techniques prompted studies to test the compatibility between current hypotheses and new findings and rendered modifications of the hypotheses necessary. After a long period dominated by the question what the sex chromosome constitution of this species might be and where the testis determining factor could be located, the presence of Sry had been eventually excluded and sex determination attributed to a hypothetical mutated gene acting downstream of Sry. An X-chromosomal or autosomal location of this gene can be assessed by cosegregation of sex with X-chromosome markers. Some preliminary results concerning X-chromosome dinucleotide repeat markers are reported. However, these markers were homomorphic in Ellobius lutescens. We now report evidence that Zfy is also missing in Ellobius lutescens and E. tancrei (males and females XX), a finding from which we conclude that the entire Y chromosome has been lost from these species. Perspectives concerning future studies are discussed.

Occurrence of gonadoblastoma in females with Turner syndrome and Y chromosome material: a population study

The presence of Y chromosome material in patients with Turner syndrome is a risk factor for the development of gonadoblastoma. However, no cases with gonadoblastoma or other ovarian malignancies have been found in epidemiological studies of cancer, morbidity, or mortality in Turner syndrome. We examined 114 females with Turner syndrome for the presence of Y chromosome material by PCR. Initially, five different primer sets were used. Y Chromosome-positive individuals were further examined with an additional four primer sets. We found 14 (12.2%; 95% confidence interval, 6.9-19.7%) patients who had Y chromosome material. The karyotype in 7 of these patients did not suggest the presence of Y chromosome material. Seven of the patients had been ovariectomized before entering the study due to verified Y chromosome material, whereas three patients were operated upon after the DNA analysis. The histopathological evaluations showed that 1 of the 10 ovariectomized patients actually had a gonadoblastoma. The rest of the patients did not have gonadoblastoma or carcinoma in situ on histopathological evaluation. Three patients (age, >50 yr) positive for Y chromosome material chose not to have ovariectomy performed, and detailed ultrasonographies did not suggest the presence of gonadoblastoma. The frequency of Y chromosome material is high in Turner syndrome (12.2%), but the occurrence of gonadoblastoma among Y-positive patients seems to be low (7-10%), and the risk may have been overestimated in previous studies, perhaps due to problems with selection bias. This study emphasizes the need for prospective unbiased studies.

Human Y chromosome, sex determination, and spermatogenesis- a feminist view

In this review I want to argue that, far from being a macho entity with an all-powerful role in male development, the human Y chromosome is a "wimp." It is merely a relic of the X chromosome, and most or all of the genes it bears-including the genes that determine sex and control spermatogenesis-are relics of genes on the X chromosome that have other functions altogether.

DXYS267: DYS393 and its X chromosome counterpart

The GATA repeat DYS393 was reported in 1987 among other Y-specific short tandem repeats. It has since been used for forensic and evolutionary studies. We decided to test its Y-specificity when we found that female DNA gave amplicons, in agreement with recent GDB-recorded experiences on radiation hybrids. Parent-child triplets revealed that heterozygous daughters always carried the same paternally derived amplicon which, however, was not amplified in their fathers' DNAs. The X-assignment was verified in larger families. A half-new primer set with a new reverse DYS393 primer, outside the old one, resulted in X amplicons in females as well as Y and X amplicons in males. This new primer set defines the new DXYS267 (GDB Data Curation). DNA-sequencing revealed four base pair differences between the Y- and the X-sequences. Two are within the reverse primer site sequence, thus probably causing preferential hybridization to the Y sequence when using the conventional primers. The two others are within the repeat array, giving the regular repeat GATA in the Y-sequence, and TATA and GACA, respectively, in the X-sequence. Allele frequency distribution in DYS393 was studied in 300 unrelated Norwegian males, allele distribution in the X-locus in 48 Norwegian women. Even if allele repeat numbers are overlapping between the loci, leading to identical fragment lengths, the allele distribution is different between DYS393 and the X-chromosome locus. The differences between the two homologous loci on the Y and X indicate a considerable lap of time since common ancestry. To avoid co-amplification of the X-locus in DYS393 typing, primer A was elongated to include one of the sequence differences between the two loci. This to a considerable extent improved the specificity of the DYS393 primers.

New uses for new haplotypes the human Y chromosome, disease and selection

Recent discoveries of many new genes have made it clear that there is more to the human Y chromosome than a heap of evolutionary debris, hooked up to a sequence that happens to endow its bearer with testes. Coupled with the recent development of new polymorphic markers on the Y, making it the best-characterized haplotypic system in the genome, this gives us new opportunities to assess its role in disease and selection, through association studies with phenotypes such as infertility and cancers. However, the peculiar genetics of this bizarre chromosome means that we should interpret such studies particularly cautiously.

Sexual dimorphism in diverse metazoans is regulated by a novel class of intertwined zinc fingers

Sex determination is regulated by diverse pathways. Although upstream signals vary, a cysteine-rich DNA-binding domain (the DM motif) is conserved within downstream transcription factors ofDrosophila melanogaster (Doublesex) and Caenorhabditis elegans (MAB-3). Vertebrate DM genes have likewise been identified and, remarkably, are associated with human sex reversal (46, XY gonadal dysgenesis). Here we demonstrate that the structure of the Doublesex domain contains a novel zinc module and disordered tail. The module consists of intertwined CCHC and HCCC Zn2+-binding sites; the tail functions as a nascent recognition α-helix. Mutations in either Zn2+-binding site or tail can lead to an intersex phenotype. The motif binds in the DNA minor groove without sharp DNA bending. These molecular features, unusual among zinc fingers and zinc modules, underlie the organization of a Drosophila enhancer that integrates sex- and tissue-specific signals. The structure provides a foundation for analysis of DM mutations affecting sexual dimorphism and courtship behavior.

Sex chromosomal transposable element accumulation and male-driven substitutional evolution in humans

We sequenced the genomic region containing the human Y-linked zinc finger gene (ZFY). Comparison of ZFY to the related region on the X chromosome (ZFX) and to autosomal sequences reveals a significant accumulation of transposable elements on the sex chromosomes. In addition, five times as many retroviruslike elements (RLEs) are present in the ZFY region as in the ZFX region. Thus, transposable elements accumulate more rapidly on the sex chromosomes, and the insertion of RLEs may occur more frequently in the male than in the female germ line. When the accumulation of substitutions in Alu elements was analyzed, it was found that the Alu elements at the Y-chromosomal locus diverged significantly faster than those at the X-chromosomal locus, whereas the divergence of autosomal Alu elements was intermediate. The male-to-female mutation rate ratio was estimated to be 2.5.

Four evolutionary strata on the human X chromosome

Human sex chromosomes evolved from autosomes. Nineteen ancestral autosomal genes persist as differentiated homologs on the X and Y chromosomes. The ages of individual X-Y gene pairs (measured by nucleotide divergence) and the locations of their X members on the X chromosome were found to be highly correlated. Age decreased in stepwise fashion from the distal long arm to the distal short arm in at least four "evolutionary strata." Human sex chromosome evolution was probably punctuated by at least four events, each suppressing X-Y recombination in one stratum, without disturbing gene order on the X chromosome. The first event, which marked the beginnings of X-Y differentiation, occurred about 240 to 320 million years ago, shortly after divergence of the mammalian and avian lineages.

Neurofibromin deficiency in mice causes exencephaly and is a modifier for Splotch neural tube defects

Neural tube defects are common and serious human congenital anomalies. These malformations have a multifactorial etiology and can be reproduced in mouse models by mutations of numerous individual genes and by perturbation of multiple environmental factors. The identification of specific genetic interactions affecting neural tube closure will facilitate our understanding of molecular pathways regulating normal neural development and will enhance our ability to predict and modify the incidence of spina bifida and other neural tube defects. Here, we report a genetic interaction between Nf1, encoding the intracellular signal transduction protein neurofibromin, and Pax3, a transcription factor gene mutated in the Splotch mouse. Both Pax3 and Nf1 are important for the development of neural crest-derived structures and the central nervous system. Splotch is an established model of folate-sensitive neural tube defects, and homozygous mutant embryos develop spina bifida and sometimes exencephaly. Neural development is grossly normal in heterozygotes and neural tube defects are not seen. In contrast, we found a low incidence of neural tube defects in heterozygous Splotch mice that also harbored a mutation in one Nf1 allele. All compound homozygotes had severe neural tube defects and died earlier in embryogenesis than either Nf1(-/-) or Sp(-/-) embryos. We also report occasional exencephaly in Nf1(-/-) mice and identify more subtle CNS abnormalities in normal-appearing Nf1(-/-) embryos. Though other genetic loci and environmental factors affect the incidence of neural tube defects in Splotch mice, these results establish Nf1 as the first known gene to act as a modifier of neural tube defects in Splotch.

Tex27, a gene containing a zinc-finger domain, is up-regulated during the haploid stages of spermatogenesis

Tex27 is a gene encoding a protein containing a zinc-finger domain in the carboxy terminal region and a transactivation domain in the amino terminal region. The Tex27 cDNA was isolated from a subtractive library that was enriched for genes preferentially expressed during the development of the seminiferous epithelium. Northern and in situ hybridization analyses demonstrated that Tex27 is differentially expressed in the testis, showing an increased expression in the germ cells corresponding to postmeiotic stages of spermatogenesis. This expression pattern in testis has been described for other C2H2-type zinc-finger proteins in mouse and human, like CTfin51, Zpf29, Sp1, and Zpf37. RFLP-Southern assays revealed that Tex27 is conserved in mammals. The polypeptide analysis and expression pattern suggest that Tex27 is a potential transcription factor preferentially expressed in postmeiotic cells during mouse spermatogenesis.

Advances in Y chromosome mapping

The human Y chromosome has long been recognized as being responsible for sex determination. In fact, it also encodes more than 30 genes and gene families that participate in a variety of cellular functions, including bone development, tooth growth, and spermatogenesis. De-novo deletion of Y chromosome segments that contain spermatogenesis genes occurs frequently, resulting in low sperm production and male infertility. This article reviews our current knowledge of the structure and function of the Y chromosome is reviewed.

ZFX transactivation of the HIV-1 LTR is cell specific and depends on core enhancer and TATA box sequences

The ZFX gene is ubiquitously transcribed and highly conserved among vertebrates. The integrity of Zfx, its murine homologue, has been shown to be important for growth during embryogenesis and sustained gamete production. Alternative splicing was shown to result in production of mRNAs coding for either ZFX804or a shorter isoform initiated downstream, ZFX575. ZFX575was previously shown to be a potent transactivator of the HLA-A11 promoter. Here, the HIV-1 LTR is also shown to be potently transactivated by ZFX575in several cell types, while ZFX804activity is found to be similar to that of ZFX575, null or intermediary according to the cell type. In all cell types, the HIV-1 TATA box sequence is a key element of transactivation, while the Sp1 or NFkappaB sites are variably required, according to the cell type. Overall, the results suggest that ZFX575and ZFX804could play a role in HIV-1 LTR induction as co-activators enhancing productive interactions between upstream transactivators and the basal transcription complexes recruited by the TATA box.

Gene interactions in gonadal development

The acquisition of a sexually dimorphic phenotype is a critical event in mammalian development. Although the maturation of sexual function and reproduction occurs after birth, essentially all of the critical developmental steps take place during embryogenesis. Temporally, these steps can be divided into two different phases: sex determination, the initial event that determines whether the gonads will develop as testes or ovaries; and sexual differentiation, the subsequent events that ultimately produce either the male or the female sexual phenotype. A basic tenet of sexual development in mammals is that genetic sex--determined by the presence or absence of the Y chromosome--directs the embryonic gonads to differentiate into either testes or ovaries. Thereafter, hormones produced by the testes direct the developmental program leading to male sexual differentiation. In the absence of testicular hormones, the pathway of sexual differentiation is female. This chapter reviews the anatomic and cellular changes that constitute sexual differentiation and discusses SRY and other genes, including SF-1, WT1, DAX-1, and SOX9, that play key developmental roles in this process. Dose-dependent interactions among these genes are critical for sex determination and differentiation.

Cloning and sequencing of buffalo male-specific repetitive DNA: sexing of in-vitro developed buffalo embryos using multiplex and nested polymerase chain reaction

Buffalo Y-chromosome specific repetitive DNA (BuRY.I) was cloned and sequenced in order to develop a sensitive method for sexing of buffalo preimplantation stage embryos using polymerase chain reaction (PCR). A highly sensitive and reliable sex determination assay using a primary (BRY.I), nested (BuRYN.I) and multiplex (BuRYN.I, ZFX/ZFY) PCR was developed. The BRY.I and BuRYN.I primers are targeted to amplify Y-specific sequences, while the ZFX/ZFY loci was amplified to serve as a positive control for both male and female samples. Accuracy of the sex determination assay was initially verified with genomic DNA obtained from blood of known gender. Further sensitivity and reproducibility of the assay was examined using DNA obtained from 1 or 2 blastomeres to demi embryos. Altogether, 80 IVF-derived embryos ranging from the 2 to 4 cell to the blastocyst stage were used for sex determination. Definite and clear signals following PCR amplification were obtained from all embryo samples. Accuracy of assays was determined by comparing results from a single cell with those of blastocyst stage embryos, thereby indicating that 1 or 2 blastomeres from a preimplantation buffalo embryo is sufficient for sex determination by PCR. No misidentification was observed within the embryo samples using nested (BuRY.I), primary (BRY.I) and multiplex (BuRYN.I; ZFX/ZFY) PCR, suggesting that this technique is a highly reliable method for sexing buffalo embryos.

XX-male syndrome bearing the sex-determining region Y

The case of a 25-year-old man who presented for evaluation of infertility is described. The physical examination revealed testicular atrophy without gynecomastia. Repeated seminal analyses showed azoospermia, and serum hormonal levels suggested a state of a hypergonadotropic hypogonadism. Chromosomal analysis demonstrated 46XX. Polymerase chain reaction revealed the existence of a sex-determining region Y. The etiology of this rare sex reversal syndrome is discussed and cases reported in Japan are reviewed.

Genetic abnormalities and male infertility. A comprehensive review

The development of assisted reproductive technologies, such as intracytoplasmic sperm injection (ICSI) substantially improved the outlook for patients with severe male fertility problems. However this implies that for the first time genetic defects associated with male in- or subfertility might be transmitted to offspring and result in genetic disease [de Kretser DM, The potential of intracytoplasmic sperm injection (ICSI) to transmit genetic defects causing male infertility. Reprod. Fertil. Dev. 1995;7:137-142]. The knowledge of male specific fertility genes on the Y chromosome increased enormously in the last decade. The SRY gene plays a critical role in gonadal differentiation. DAZ, SPGY and related genes on the Y chromosome are very important for spermatogenesis. Interstitial Y-chromosomal microdeletions encompassing the AZFa, b or c region have become an additional class of genetic abnormalities causing male infertility. A review is given of the different genetic aspects of male infertility.

Evidence for a Turner syndrome locus or loci at Xp11.2-p22.1

Turner syndrome is the complex human phenotype associated with complete or partial monosomy X. Principle features of Turner syndrome include short stature, ovarian failure, and a variety of other anatomic and physiological abnormalities, such as webbed neck, lymphedema, cardiovascular and renal anomalies, hypertension, and autoimmune thyroid disease. We studied 28 apparently nonmosaic subjects with partial deletions of Xp, in order to map loci responsible for various components of the Turner syndrome phenotype. Subjects were carefully evaluated for the presence or absence of Turner syndrome features, and their deletions were mapped by FISH with a panel of Xp markers. Using a statistical method to examine genotype/phenotype correlations, we mapped one or more Turner syndrome traits to a critical region in Xp11.2-p22.1. These traits included short stature, ovarian failure, high-arched palate, and autoimmune thyroid disease. The results are useful for genetic counseling of individuals with partial monosomy X. Study of additional subjects should refine the localization of Turner syndrome loci and provide a rational basis for exploration of candidate genes.

Prenatal identification of mos 45,X/46,X,+mar in a normal male baby by cytogenetic and molecular analysis

We report a case of mos 45,X/46,X,+mar, diagnosed prenatally by amniocentesis, whose physical examination, including external and internal organs, along with serum testosterone values were normal five years after delivery. The mosaic karyotype was seen in 146 of 240 cells examined (amniotic fluid cells, 110/65; placental chorionic villi: 5/4; cord blood, 21/81; cultured skin fibroblasts, 10/90) from 386 metaphases, and the marker chromosome appeared as a small non-fluorescent acrocentric chromosome. All autosomes appeared normal, and no normal Y chromosome could be demonstrated. Analysis of 26 Y-chromosome loci by molecular techniques such as PCR, Southern analysis using multiple Y-specific DNA probes, and Hae III restriction endonuclease assessment of male-specific repeated DNA in the heterochromatic region of the Y chromosome, and fluorescence in situ hybridization (FISH), revealed the marker was derived from a Y chromosome including p terminal to q11.23, and paracentric inversion in the remaining Y long arm. The formation of testes can be considered as existence of SRY (sex-determining region of Y) as a testis-determining factor. The present report illustrates the importance of FISH and molecular techniques as a complement to cytogenetic methods for accurate identification and characterization of chromosome rearrangements in prenatal diagnosis.

Seminoma in a postmenopausal woman with a Y;15 translocation in peripheral blood lymphocytes and a t(Y;15)/45,X Turner mosaic pattern in skin fibroblasts

We report an unusual case of a 55 year old Japanese woman with a seminoma but relatively normal menses. The patient was a phenotypic female with late onset menarche (18 years of age), who was amenorrhoeic for the first year, followed by menses of one to three days' slight flow with dysmenorrhoea, but an otherwise normal menstrual history. A typical seminoma was removed from the left adnexal region and an immature testis was identified separately as an associated right adnexal mass. Repeated karyotypic studies on peripheral blood lymphocyte cultures showed only 46,X,-Y,t(Y;15)(q12;p13). Cytogenetic examination of the patient's younger brother, who had fathered three healthy children, showed an identical karyotype. Mosaicism of 46,X,-Y,t(Y;15)(q12;p13)/45,X cell lines was found in skin samples from the patient's elbow and genital regions, although there were no clinical stigmata of Turner syndrome. An androgen receptor binding assay of cultured genital skin fibroblasts was negative. Molecular analysis using Southern blot hybridisation, PCR, and direct DNA sequencing showed that neither the patient nor her brother had a detectable deletion or other abnormalities of Y chromosome sequences, including the SRY (sex determining region of the Y chromosome) gene sequence. These findings suggest that Turner mosaicism of the 45,X cell line may have contributed to this atypical presentation in an XY female, although we cannot exclude abnormalities of other genes related to sex differentiation.

The mouse Y chromosome interval necessary for spermatogonial proliferation is gene dense with syntenic homology to the human AZFa region

The Delta Sxrb deletion interval of the mouse Y chromosome contains Spy, a spermatogenesis factor gene(s) whose expression is essential for the postnatal development of the mitotic germ cells, spermatogonia. The boundaries of Delta Sxrb are defined by the duplicated genes Zfy1 and Zfy2 and four further genes have previously been mapped within the interval: Ube1y and Smcy, linked with Zfy1 on a contig of 250 kb, and Dffry and Uty, which were unanchored. The interval was estimated to be >450 kb. In order to identify any further gene(s) that may underlie Spy, systematic exon trapping was performed on an extended contig, anchored on Zfy1, which covers 750 kb of the Delta Sxrb interval. Exons from two novel genes were isolated and placed together with Dffry and Uty on the contig in the order Dffry-Dby-Uty-Tspy-Eif2gammay-Smcy- Ube1y-Zfy1. All the genes, with the double exception of Tspy, are X-Y homologous and produce putatively functional, spliced transcripts. The tight linkage and order of Dffry, Dby and Uty was shown to be conserved in deletion intervals 5C/5D of the human Y chromosome by the construction of a contig of human PAC and YAC clones; this represents the first example of syntenic homology between Y chromosomes from two distinct mammalian orders. Interval 5C/5D contains the distal boundary of the AZFa interval, which, like Delta Sxrb, is believed to be necessary for spermatogonial development in the prepubertal testis. Our results therefore show that AZFa and Spy may be encoded by homologous genes.

A proposed path by which genes common to mammalian X and Y chromosomes evolve to become X inactivated

Mammalian X and Y chromosomes evolved from an autosomal pair; the X retained and the Y gradually lost most ancestral genes. In females, one X chromosome is silenced by X inactivation, a process that is often assumed to have evolved on a broadly regional or chromosomal basis. Here we propose that genes or clusters common to both the X and Y chromosomes (X-Y genes) evolved independently along a multistep path, eventually acquiring dosage compensation on the X chromosome. Three genes studied here, and other extant genes, appear to be intermediates. ZFX, RPS4X and SMCX were monitored for X inactivation in diverse species by assaying CpG-island methylation, which mirrors X inactivation in many eutherians. ZFX evidently escaped X inactivation in proto-eutherians, which also possessed a very similar Y-linked gene; both characteristics were retained in most extant orders, but not in myomorph rodents. For RPS4X, escape from X inactivation seems unique to primates. SMCX escapes inactivation in primates and myomorphs but not in several other lineages. Thus, X inactivation can evolve independently for each of these genes. We propose that it is an adaptation to the decay of a homologous, Y-linked gene.

Turner syndrome and haploinsufficiency

Turner syndrome was one of the first human genetic disorders ascribed to haploinsufficiency but the identification of specific genes responsible for the phenotype has been problematic. Recent data point to several candidate genes, some new and some old, for specific aspects of the phenotype associated with monosomy X in humans.

The mammalian Y chromosome: a new perspective

For several decades, the mammalian Y chromosome was considered a genetic "desert," with the testis determinant being the sole survivor of the attrition that followed the chromosome's inception. Aside from the addition of a genetic factor required for spermatogenesis to the human Y chromosome in 1976, this view held sway until the mid-1980s. The ensuing molecular genetic analysis, culminating in the recent paper in Science by Lahn and Page, has identified more than 20 genes or gene families on the human Y. This has led to a reappraisal of the evolution and functions of this unique chromosome.

Frequency of Y chromosomal material in Mexican patients with Ullrich-Turner syndrome

Cytogenetic studies have shown that 40-60% of patients with Ullrich-Turner syndrome (UTS) are 45,X, whereas the rest have structural aberrations of the X chromosome or mosaicism with a second cell line containing a structurally normal or abnormal X or Y chromosome. However, molecular analysis has demonstrated a higher proportion of mosaicism, and studies in different populations have shown an extremely variable frequency of Y mosaicism of 0-61%. We used Southern blot analysis and polymerase chain reaction (PCR) to detect the presence of Ycen, ZFY, SRY, and Yqh in 50 Mexican patients with UTS and different karyotypes to determine the origin of marker chromosomes and the presence of Y sequences. Our results indicated the origin of the marker chromosome in 1 patient and detected the presence of Y sequences in 4 45,X patients. Taken together, we found a 12% incidence of Y sequences in individuals with UTS. The amount of Y-derived material was variable, making the correlation between phenotype and molecular data difficult. Only 1 patient had a gonadoblastoma. We discuss the presence of Y chromosomes or Y sequences in patients with UTS and compare our frequency with that previously reported.

Patterns of Y and X chromosome DNA sequence divergence during the Felidae radiation

The 37 species of modern cats have evolved from approximately eight phylogenetic lineages within the past 10 to 15 million years. The Felidae family has been described with multiple measures of morphologic and molecular evolutionary methods that serve as a framework for tracking gene divergence during brief evolutionary periods. In this report, we compare the mode and tempo of evolution of noncoding sequences of a large intron within Zfy (783 bp) and Zfx (854 bp), homologous genes located on the felid Y and X chromosomes, respectively. Zfy sequence variation evolves at about twice the rate of Zfx, and both gene intron sequences track feline hierarchical topologies accurately. As homoplasies are infrequent in patterns of nucleotide substitution, the Y chromosome sequence displays a remarkable degree of phylogenetic consistency among cat species and provides a highly informative glimpse of divergence of sex chromosome sequences in Felidae.

Cloning and mapping of bovine ZFX gene to the long arm of the X-chromosome (Xq34) and homologous mapping of ZFY gene to the distal region of the short arm of the bovine (Yp13), ovine (Yp12-p13), and caprine (Yp12-p13) Y chromosome

A part of mouse Zfy-2 sequence was synthesized and used to screen a genomic library of the spinous country-rat (Tokudaia osimensis spp., 2n = 45). An isolated clone had the C-terminal region of Zfy, which consisted of 1190 bp, encoded 336 amino acid residues, and harbored 11 out of 13 zinc finger motifs. With this as a probe, a bovine testis cDNA library was screened. Two ZFX clones were isolated and their sequences combined. The short sequence, lacking part of the 5' upstream region, was amplified by PCR or RT-PCR, cloned, and sequenced. A full-length ZFX was constructed by combining these three sequences. The bovine ZFX consisted of 5328 bp and encoded 800 amino acid residues, which contained 13 zinc finger motifs. ZFX was used as a probe for fluorescence in situ hybridization and was mapped to Xq34, different from its previously reported site at Xq21-q231. A SINE (short interspersed nuclear element) sequence consisting of 188 bp was found close to the end of the 3'-untranslated region of ZFX. The SINE sequence hybridized to all bovine chromosomes. ZFY is highly homologous with ZFX and, as a result, ZFY could be mapped simultaneously. ZFY was mapped to the distal region of the short arm of the Y Chromosome (Chr) (Yp13), contradicting the previously reported position Yq1. Ovine and caprine ZFY were also mapped with bovine ZFX. Both were mapped to the distal region of the short arm of the Y Chr (Yp12-p13). Ovine ZFX was mapped to a region close to the centromere of the X Chr (Xq13).

Regulation of sexual dimorphism in mammals

Sexual dimorphism in humans has been the subject of wonder for centuries. In 355 BC, Aristotle postulated that sexual dimorphism arose from differences in the heat of semen at the time of copulation. In his scheme, hot semen generated males, whereas cold semen made females (Jacquart, D., and C. Thomasset. Sexuality and Medicine in the Middle Ages, 1988). In medieval times, there was great controversy about the existence of a female pope, who may have in fact had an intersex phenotype (New, M. I., and E. S. Kitzinger. J. Clin. Endocrinol. Metab. 76: 3-13, 1993.). Recent years have seen a resurgence of interest in mechanisms controlling sexual differentiation in mammals. Sex differentiation relies on establishment of chromosomal sex at fertilization, followed by the differentiation of gonads, and ultimately the establishment of phenotypic sex in its final form at puberty. Each event in sex determination depends on the preceding event, and normally, chromosomal, gonadal, and somatic sex all agree. There are, however, instances where chromosomal, gonadal, or somatic sex do not agree, and sexual differentiation is ambiguous, with male and female characteristics combined in a single individual. In humans, well-characterized patients are 46, XY women who have the syndrome of pure gonadal dysgenesis, and a subset of true hermaphrodites are phenotypic men with a 46, XX karyotype. Analysis of such individuals has permitted identification of some of the molecules involved in sex determination, including SRY (sex-determining region Y gene), which is a Y chromosomal gene fulfilling the genetic and conceptual requirements of a testis-determining factor. The purpose of this review is to summarize the molecular basis for syndromes of sexual ambiguity seen in human patients and to identify areas where further research is needed. Understanding how sex-specific gene activity is orchestrated may provide insight into the molecular basis of other cell fate decisions during development which, in turn, may lead to an understanding of aberrant cell fate decisions made in patients with birth defects and during neoplastic change.

Reconstructing hominid Y evolution: X-homologous block, created by X-Y transposition, was disrupted by Yp inversion through LINE-LINE recombination

The human X and Y chromosomes share many blocks of similar DNA sequence. We conducted mapping and nucleotide sequencing studies of extensive, multi-megabase homologies between Yp and Xq21, which do not recombine during male meiosis. We confirmed and built upon previous evidence that a Yp inversion had occurred during evolution: a single contiguous segment of Xq21 is homologous to two non-contiguous segments of Yp. We precisely defined and sequenced the inversion breakpoints, obtaining evidence that the inversion was mediated by recombination between LINE-1 elements in otherwise non-homologous regions. This inversion appears to have followed a single transposition of an approximately 4 Mb segment from the X to the Y chromosome. These events jointly account for the present arrangement of Yp-Xq21 homologous sequences. Based on Southern blotting studies of primates and of humans drawn from diverse populations, we conclude that both the X-Y transposition and the subsequent, LINE-mediated Yp inversion occurred after the divergence of hominid and chimp lineages but before the radiation of extant human populations. This evolutionary scenario is consistent with our finding of 99.3 +/- 0.2% nucleotide identity between the X and Y chromosomes within the transposed region, which suggests that the transposition occurred approximately 3-4 million years ago, near the time of emergence of Homo . Comparative sequencing of the entire human X and Y chromosomes may reveal a succession of transpositions, inversions and other rearrangements underlying the complex pattern of sequence similarities between the present-day sex chromosomes. With the possible exception of cubitus valgus, phenotypic features of Turner syndrome are absent in individuals monosomic for Yp-Xq21 homologous sequences, suggesting that most of the critical 'Turner genes' are found elsewhere on the X and Y chromosomes.