Mammalian gonadal determination and gametogenesis

Dynamic and modular gene regulatory networks drive the development of gametogenesis

Gametogenesis is a complex process, which includes mitosis and meiosis and results in the production of ovum and sperm. The development of gametogenesis is dynamic and needs many different genes to work synergistically, but it is lack of global perspective research about this process. In this study, we detected the dynamic process of gametogenesis from the perspective of systems biology based on protein-protein interaction networks (PPINs) and functional analysis. Results showed that gametogenesis genes have strong synergistic effects in PPINs within and between different phases during the development. Addition to the synergistic effects on molecular networks, gametogenesis genes showed functional consistency within and between different phases, which provides the further evidence about the dynamic process during the development of gametogenesis. At last, we detected and provided the core molecular modules of different phases about gametogenesis. The gametogenesis genes and related modules can be obtained from our Web site Gametogenesis Molecule Online (GMO, http://gametsonline.nwsuaflmz.com/index.php), which is freely accessible. GMO may be helpful for the reference and application of these genes and modules in the future identification of key genes about gametogenesis. Summary, this work provided a computational perspective and frame to the analysis of the gametogenesis dynamics and modularity in both human and mouse.

An efficient method of generating transgenic mice by pronuclear microinjection

Genetic transformation of mice using pronuclear microinjection was demonstrated by a number of groups in rapid succession in the early 1980's. Since that time, studies using transgenic animals have produced major advances in biomedical sciences and molecular genetics. More important, it is possible to study the molecular basis for tissue and stage-specific expression of genes. We recently used this method to generate transgenic mice. DNA fragment (transgene) was injected into the pronucleus of one-cell embryos. We describe this simplified protocol, which is reliable. With the use of buffered medium M2 for the whole process, it is not mandatory to have a CO2 incubator.

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.

Cryptorchidism. Current concepts

Cryptorchidism is the most common genitourinary disorder of childhood. Even though its incidence has changed only slightly over the years, the number of operations for cryptorchid testes has tripled. Better understanding of the natural history of cryptorchidism, as well as changes that occur in testicular histology both in the cryptorchid and the contralateral descended testis very early in life, are the cause. This experience has led us to advocate early orchiopexy as the optimum means of treatment.

Expression of the rat testis-specific histone H1t gene in transgenic mice. One kilobase of 5'-flanking sequence mediates correct expression of a lacZ fusion gene

H1t is synthesized in mid to late pachytene spermatocytes of the male germ line and is the only tissue-specific member of the mammalian H1 histone family. As a step toward identifying DNA sequences that confer its tissue-specific expression, we have produced transgenic mice containing the intact rat H1t gene as well as a H1t-lacZ fusion gene. Transgenic mice carrying a 6.8-kilobase fragment of rat genomic DNA encompassing the H1t gene expressed rat H1t at high levels in the testis and in no other organ examined. H1t fragments truncated to within 141 base pairs (bp) of the gene in the 5' direction or within 837 bp in the 3' direction retained testis specificity. Expression of rat H1t protein was also evident in the testes of the transgenic mice, and in some lines the level of rat H1t exceeded that of the mouse protein. The stage of spermatogenesis of transgene expression was assessed by following appearance of transgenic mRNA in developing mice and by immunohistochemistry using an antiserum to rat H1t. In lines from three different constructs, expression was restricted to germinal cells, although in two strongly expressing lines the transgenes were expressed somewhat prematurely in preleptotene spermatocytes. An H1t(-948/+71)-lacZ fusion was also expressed specifically in the spermatocytes and round spermatids of a transgenic line, confirming that sequences sufficient for correct tissue and developmental expression lie within this 1,019-bp segment of the gene.

Cognitive functioning in female patients with 21-hydroxylase deficiency

The cognitive functioning of 27 female patients with congenital adrenal hyperplasia (CAH) (aged 11-41 yrs) and 13 of their healthy sisters (13-31 yrs) was compared using short versions of age-appropriate Wechsler scales. In contrast to other studies, neither a higher than average IQ level for CAH patients (mean: 99.0) nor for their sisters (97.7) was found. Unexpectedly, and in contrast to other reports, the subgroup of salt-wasting (SW) patients>16 yrs (N=6; mean score: 111.5) differed from their sisters as well as from simple-virilizing (SV) patients in "full IQ" (p<0.05) and subtest scorings for "Information", "Similarities", and "Picture Completion" (p<0.05-<0.10). SW patients displayed "more masculine" behaviour (vs. SV patients and sisters) which, in turn, was related to differential prenatal hormonal influences. No clear-cut relationships between IQ/cognitive (subtest) findings and gender-role behaviour were found.

The undescended testis. Hormonal and surgical management

Cryptorchidism is the most common disorder of sexual differentiation in males, with an incidence of 3.4 per cent in the term newborn, decreasing to 0.8 per cent at 1 year of age. The mechanisms of normal testicular descent are multifactorial and include an intact hypothalamic-pituitary-testicular axis, as well as a normal gubernaculum and epididymis. In boys with cryptorchidism, the testes demonstrate degenerative changes histologically as early as 1 to 2 years of age. Both testes may be affected, even with a unilateral undescended testis. The most important long-term complications of cryptorchidism include infertility and testicular cancer. The risk of malignancy is 10 to 40 times higher in men with cryptorchidism than in normal men and is highest in men who have had an intra-abdominal testis and in certain intersex conditions. Orchiopexy does not appear to lessen this risk. In clinical trials in the United States, hormonal therapy with hCG or GnRH has not been effective in causing testicular descent; therefore, orchiopexy remains standard treatment. However, hCG is recommended if the clinician suspects that a testis is retractile. Orchiopexy should be performed between 12 and 18 months of age to prevent the degenerative changes that are demonstrable by 2 years.

Characterization of Y chromosomal deoxyribonucleic acid fragments and translocations by Southern blot analysis

Hybridization of Y chromosome-specific probes to Southern blots of genomic deoxyribonucleic acid from patients with chromosomal variants permits direct and rapid characterization of the chromosomal content. We have used two single-copy Y chromosomal sequences specific for the short arm (47z and DP34) and one repeated sequence specific to the long arm (Y3.4) to study several patients with different types of sex chromosomal abnormalities, including three patients with gonadal dysgenesis and the karyotype 45,X/46,X + fragment, two females with Y autosomal translocations involving similar regions of the Y chromosome (46,XX,t(Y;14)(q11,p11) and 46,XY,t(Y;15)(q11,p11), two males with very small Y chromosomes (del(Y)(q12) and i(Yp], and a 45,X male with a small Y autosomal translocation. These techniques are more sensitive than chromosome banding and thus are an important adjunct to karyotyping for analysis of chromosomal content. For patients with gonadal dysgenesis and uncharacterized fragments, demonstration of Y chromosomal sequences identifies an important risk factor for the development of gonadoblastoma. For other patients, accurate identification of Y chromosomal content may facilitate prediction of the patient's phenotype.

Cryptorchidism: isolated and associated with other genitourinary defects

Cryptorchidism is the most common disorder of sexual differentiation in male children, with an incidence of 3.4 per cent in the term newborn, decreasing to 0.8 per cent at 1 year of age. The mechanisms of normal testicular descent are multifactorial and include an intact hypothalamic-pituitary-testicular axis, as well as a normal gubernaculum and epididymis. In boys with cryptorchidism, the testes demonstrate degenerative changes histologically as early as 1 to 2 years of age. Both testes may be affected, even with a unilateral undescended testis. The most important long-term complications of cryptorchidism include infertility and testicular cancer. The risk of malignancy is approximately 40 times higher in male subjects with cryptorchidism than in normal men, and is highest in male subjects who have had an intra-abdominal testis and in certain intersex conditions. Orchiopexy does not appear to lessen this risk. Hormonal therapy with HCG or LH-RH has remained unproven in clinical trials in the United States; therefore, orchiopexy remains standard treatment. HCG is recommended if the clinician suspects that a testis is retractile, however. Orchiopexy should be performed between 12 and 18 months of age to prevent the degenerative changes that are demonstrable by 2 years.

The human Y chromosome

Despite its central role in sex determination, genetic analysis of the Y chromosome has been slow. This poor progress has been due to the paucity of available genetic markers. Whereas the X chromosome is known to include at least 100 functional genetic loci, only three or four loci have been ascribed to the Y chromosome and even the existence of several of these loci is controversial. Other factors limiting genetic analysis are the small size of the Y chromosome, which makes cytogenetic definition difficult, and the absence of extensive recombination. Based on cytogenetic observation and speculation, a working model of the Y chromosome has been proposed. In this classical model the Y chromosome is defined into subregions; an X-Y homologous meiotic pairing region encompassing most of the Y chromosome short arm and, perhaps, including a pseudoautosomal region of sex chromosome exchange; a pericentric region containing the sex determining gene or genes; and a long arm heterochromatic genetically inert region. The classical model has been supported by studies on the MIC2 loci, which encode a cell surface antigen defined by the monoclonal antibody 12E7. The X linked locus MIC2X, which escapes X inactivation, maps to the tip of the X chromosome short arm and the homologous locus MIC2Y maps to the Y chromosome short arm; in both cases, these loci are within the proposed meiotic pairing region. MIC2Y is the first biochemically defined, expressed locus to be found on the human Y chromosome. The proposed simplicity of the classical model has been challenged by recent molecular analysis of the Y chromosome. Using cloned probes, several groups have shown that a major part of the Y chromosome short arm is unlikely to be homologous to the X chromosome short arm. A substantial block of sequences of the short arm are homologous to sequences of the X chromosome long arm but well outside the pairing region. In addition, the short arm contains sequences shared with the Y chromosome long arm and sequences shared with autosomes. About two-thirds of XX males contain detectable Y derived sequences. As the amount of Y sequences present varies in different XX males, DNA from these subjects can be used to construct a map of the region around the sex determining gene. Assuming that XX males are usually caused by simple translocation, the sex determining genes cannot be located in the pericentric region. Although conventional genetic analysis of the Y chromosome is difficult, this chromosome is particularly suited to molecular analysis. Paradoxically, the Y chromosome may soon become the best defined human chromosome at the molecular level and may become the model for other chromosomes.

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

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

A sex-determining gene, fem-1, required for both male and hermaphrodite development in Caenorhabditis elegans

Sex in the nematode Caenorhabditis elegans is normally determined by the X chromosome to autosome (X:A) ratio, with XX hermaphrodites and XO males. Previous work has shown that a set of at least four autosomal genes (her-1, tra-2, tra-3, and tra-1) is signaled by the X:A ratio and appears to act in a regulatory pathway to determine sex. Twenty-one new recessive alleles of the gene fem-1(IV) (formerly isx-1) have been isolated. Seven of these may be null alleles; one of these is an amber mutation. The other 14 alleles are temperature sensitive. The putative null mutations cause both XO and XX animals to develop as females when the mother as well as the zygote is fem-1(-). Therefore, fem-1(+) is required (a) for the development of the male body and (b) for spermatogenesis in males and hermaphrodites. In addition, fem-1 shows a maternal effect: wild-type fem-1 product partially rescues the development of fem-1(-) progeny. By analyzing double mutants it has been shown that fem-1(+) is part of the sex-determination pathway and has two distinct functions: (1) in the soma it prevents the action of tra-1, thereby allowing male development to occur, and (2) in the germline it is necessary for spermatogenesis in both sexes.

Extensive sequence homologies between Y and other human chromosomes

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

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes

Previous theoretical considerations and some experimental data have suggested a role for DNA methylation in the maintenance of mammalian X chromosome inactivation. The isolation of specific X-encoded sequences makes it possible to investigate this hypothesis directly. We have used cloned fragments of the human hypoxanthine phosphoribosyltransferase (HPRT) gene and methylation-sensitive restriction enzymes to study methylation patterns in genomic DNA of individuals with different numbers of X chromosomes and in somatic cell hybrid lines containing human X chromosomes that are either active or inactive or have been reactivated by treatment with 5-azacytidine. The results of these analyses show that there is hypomethylation of active X chromosomes relative to inactive X chromosomes in the 5' region of this gene. In the middle region of the gene, however, a site that is consistently undermethylated on inactive X chromosomes was identified. Taken together, the data suggest that the overall pattern of methylation, rather than methylation of specific sites, plays a role in the maintenance of X chromosome inactivation.

Human XX males with Y single-copy DNA fragments

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

H-Y antigen negativity associated with a normal male phenotype

The 46, XY, 45, X mosaicism is a complement found only once among 39,557 males at birth [18]. The spectrum of phenotypes associated with this mosaicism is continuous ranging from female phenotype with or without Turner syndrome, to mixed gonadal dysgenesis, hermaphroditism, or occasionally almost normal males [24]. In such mosaicism the Y chromosome is usually rearranged: mainly i(Y) and dic(Y) but also del(Y) and r(Y). In a few cases the cell line with 46 chromosomes contains a minute marker which was assumed to be a Y-fragment (Y-f) or a del(Yq) because of the presence of testicular tissue in subjects with sexual ambiguity [20]. We now report the case of a normal but sterile man with a 45, X/46, X, Y-f caryotype who is HY antigen-negative.

The genetics of hormonal influences on male sexual behavior of mice and rats

This review focuses on the intersection of genes and hormones as they relate to the development of male sexual behavior. Three major hypotheses are discussed: (1) Some differences in adult male sexual behavior are due to gene differences that influence brain differentiation. Genes that influence brain differentiation may do so by affecting the elaboration of testosterone (i.e., H-Y antigen) or the sensitivity to testosterone (i.e., Tfm mutation and autosomal variations) during neonatal and/or prenatal life. (2) Some differences in male sexual behavior are due to gene differences that influence adult levels of testosterone or sensitivity to testosterone and its metabolites. (3) There is a gene(s) on the Y chromosome that influences the development of sexual behavior that is associated with the arousal mechanism. A possible hormonal mechanism of this Y chromosomal gene(s) is discussed.

Isolation of recombinant bacteriophage containing male-specific mouse DNA

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

The application of DNA recombinant technology to the analysis of the human genome and genetic disease

Recombinant DNA technology permits the isolation of libraries of DNA sequences corresponding to either the whole genome of an individual or the expressed sequences of a given cell type. Gene-specific probes isolated from these libraries may be used for the identification of DNA sequences in the genome necessary for normal gene function and for the study of the consequences of mutations and rearrangements in these sequences which give rise to the clinical symptoms in genetic disease. DNA sequence polymorphisms can be used to construct a genetic linkage map of the entire human genome. This allows the development of antenatal diagnoses for monogenic diseases even in the absence of an understanding of the biochemical defect.

Mechanisms of gonadal differentiation

Sex differentiation is the result of the translation of genetic sex into gonadal sex. Without recognizable masculinizing signals the embryonic gonad will undergo ovarian differentiation. The main determinant of gonadal differentiation appears to be the presence or absence of a cell surface antigen, called H-Y antigen. The regulation of H-Y antigen expression is complex and involves the interaction between regulatory sites on the Y chromosome, the X chromosome, and possibly the autosomes.

Testosterone: a major determinant of extragenital sexual dimorphism

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