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Biomedical subjects

R M Speed

Publications and source records attributed to R M Speed.

At least 19 recordsLinked to original sources
PubMed2002

Partial rescue of the Dazl knockout mouse by the human DAZL gene.

Y-chromosomal DAZ (deleted in azoospermia) and autosomal DAZ-like (DAZL) comprise a gene family involved in gametogenesis. Y-chromosomal and autosomal genes only co-exist in humans and old world monkeys, indicating that DAZ genes are a recent acquisition of the Y chromosome. In most mammals, the ancestral Dazl alone is sufficient to complete gametogenesis. It is not yet understood why humans and old world monkeys have a second set of genes that are apparently necessary for spermatogenesis, since deletions removing the Y-chromosomal DAZ are often associated with azoo- or oligospermia. We used transgenic mice carrying either human DAZL or human DAZ on a mouse Dazl null background to investigate the functions of the human homologues. Both transgenes enabled prophase spermatocytes to be produced, mainly of the leptonema/zygonema stage, but failed to promote differentiation into mid- to late pachytenes. The presence of human DAZL resulted in a larger amount of early germ cells compared with that observed in DAZ. The degree of rescue was independent of copy number, integration site or presence of the DAZ repeat region for the DAZ transgenes. These findings confirm that DAZL and DAZ can only substitute for early functions of the murine homologue resulting in the establishment of the germ cell population and partial progression into meiosis.

Animals↗
PubMed2000

Meiotic studies of a human male carrier of the common translocation, t(11;22), suggests postzygotic selection rather than preferential 3:1 MI segregation as the cause of liveborn offspring with an unbalanced translocation.

The t(11;22)(q23;q11) translocation is the only non-Robertsonian rearrangement for which there are a large number of unrelated families, apparently with the same breakpoints. These families most often have been ascertained through an abnormal child with the karyotype 47,XX or XY, +der(22) t(11;22)(q23;q11). To explain the high incidence of 3:1 segregants, rarely seen in offspring of carriers of other reciprocal translocations, a number of theoretical models have been suggested. We have used both electron microscope analysis of the synaptonemal complex (SC) and dual-color FISH to investigate the meiotic chromosome behavior in a male carrier of the translocation who has the karyotype 46,XY, t(11;22)(q23;q11). Chromosome synapsis, first-meiotic chiasma configuration, and segregation behavior of this translocation have been analyzed directly. Examination of SCs by electron microscopy showed pachytene-cross formation in 49/50 nuclei. Approximately 50% (26/50) revealed a classical fully synapsed quadrivalent. A proportion of these (10/26), however, showed some central asymmetry, suggesting heterologous synapsis. The remaining cells appeared to have incomplete synapsis. FISH analysis showed only quadrivalents in all 100 metaphase I nuclei. The chiasma frequency was increased within the interstitial segments, in comparison with the same region in normal bivalents. All types of segregation category were found in metaphase II nuclei. There was no indication of preferential 3:1 anaphase I segregation. We conclude that the +der(22) constitution in offspring of carriers of t(11;22)(q23;q11) is not likely to be due to meiotic 3:1 segregation being especially common. Rather, the +der(22) constitution is more likely to be the result of postzygotic selection against other unbalanced karyotypes.

Cell Nucleus↗
PubMed1999

Deficiency of Trp53 rescues the male fertility defects of Kit(W-v) mice but has no effect on the survival of melanocytes and mast cells.

Mutations of the receptor tyrosine kinase, Kit, or its ligand, mast growth factor (Mgf), affect three unrelated cell populations: melanocytes, germ cells, and mast cells. Kit signaling is required initially to prevent cell death in these lineages both in vitro and in vivo. Mgf appears to play a role in the survival of some hematopoietic cells in vitro by modulating the activity of p53. Signaling by Mgf inhibits p53-induced apoptosis of erythroleukemia cell lines and suppresses p53-dependent radiation-induced apoptosis of bone marrow cells. We tested the hypothesis that cell survival in Kit mutant mice would be enhanced by p53 deficiency in vivo. Double-mutant mice, which have greatly reduced Kit receptor tyrosine kinase activity and also lack Trp53, were generated and the affected cell lineages examined. Mast cell, melanoblast, and melanocyte survival in the double Kit(W-v/W-v):Trp53(-/-) mutants was not increased compared to the single Kit(W-v/W-v):Trp53(+/+) mutants. However, double-mutant males showed an increase in sperm viability and could father litters, in contrast to their homozygous Kit mutant, wild-type p53 littermates. This germ cell rescue appears to be male specific, as female ovaries were similar in mice homozygous for the Kit mutant allele with or without p53. We conclude that defective Kit signaling in vivo results in apoptosis by a p53-independent pathway in melanocyte and mast cell lineages but that in male germ cells apoptosis in the absence of Kit is p53-dependent.

Animals↗
PubMed1999

A human DAZ transgene confers partial rescue of the mouse Dazl null phenotype.

In a subset of infertile men, a spectrum of spermatogenic defects ranging from a complete absence of germ cells (sertoli cell only) to oligozoospermia is associated with microdeletions of the DAZ (deleted in azoospermia) gene cluster on human distal Yq. DAZ encodes a testis-specific protein with RNA-binding potential recently derived from a single-copy gene DAZL1 (DAZ-like) on chromosome 3. Y chromosomal DAZ homologues are confined to humans and higher primates. It remains unclear which function unique to higher primate spermatogenesis DAZ may serve, and the functional status of the gene recently has been questioned. To assess the extent of functional conservation we have tested the capacity of a human DAZ gene contained in a 225-kb yeast artificial chromosome to complement the sterile phenotype of the Dazl null mouse (Dazl-/-), which is characterized by severe germ-cell depletion and meiotic failure. Although Dazl-/- mice remained infertile when the DAZ transgene was introduced, histological examination revealed a partial and variable rescue of the mutant phenotype, manifest as a pronounced increase in the germ cell population of the seminiferous tubules and survival to the pachytene stage of meiosis. As well as constituting definitive proof of the spermatogenic role of the DAZ gene product, these findings confirm the high degree of functional conservation between the DAZ and DAZL1 genes, suggesting they may constitute a single target for contraceptive intervention and raising the possibility of therapeutic up-regulation of the DAZL1 gene in infertile men.

Animals↗
PubMed1999

Mice with Y chromosome deletion and reduced Rbm genes on a heterozygous Dazl1 null background mimic a human azoospermic factor phenotype.

A subset of azoospermia or oligozoospermia patients have microdeletions in defined regions of their Y chromosome, namely the AZFa, b, and c regions. Candidate genes in humans that may cause the azoospermia factor (AZF) phenotype have been assigned to these regions and can include the DAZ and RBM genes. Part of the variability in the AZFc phenotype might be due to interaction between the effects of deleting the DAZ and RBM genes. We mimicked human deletions of RBM and DAZ in the mouse by crossing male mice with a deleted Y chromosome with a reduced number of Rbm genes (Y(d1)) to heterozygote Dazl1 null female mice to study the interaction of the Dazl1 and Rbm or other genes located in the Y(d1) deletion interval. Dazl-/+ Y(d1) animals showed a significant reduction in the sperm count (P < 0.001), an increase of abnormal sperm heads and prominent mid-piece defects of the tails compared to either mutation alone (P < 0.001). Hence, Dazl1 and the genes removed on the Y(d1) chromosome are active in different pathways contributing to different stages of spermatogenesis. Reduction of Dazl1 and Rbm genes as well as/or deletion of the Y chromosome in mice gives rise to a phenotype similar to the heterogeneous AZFc phenotype observed in humans.

Animals↗
PubMed1997

Fertility investigations in the F1 hybrid and backcross progeny of cattle (Bos taurus) and yak (B. grunniens) in Mongolia.

Investigations conducted in Mongolia into the sterility of the male khainag, an F1 hybrid animal resulting from crossing cattle (Bos taurus, 2n = 60) with yaks (B. grunniens, 2n = 60), are reported. Reduced numbers of spermatogonia appear to characterise the testicular tubules of the khainag, and despite the identical cytological appearance of the two parental karyotypes, synaptic anomalies are seen at meiotic prophase in primary spermatocytes. The female khainag is fertile and can be backcrossed to cattle or yak bulls to produce a B1 backcross animal, the ortoom. Further backcrossing of ortoom females to cattle or yaks will yield a B2 backcross animal, the usanguzee. The impression is gained of better meiotic pairing in the backcross animals than in the khainag. The "Haldane Rule" is followed perfectly by the cattle x yak hybrid; namely, sterility is confined to the male.

Animal Husbandry↗
PubMed1996

Different distributions of homologous chromosomes in adult human Sertoli cells and in lymphocytes signify nuclear differentiation.

Using whole chromosome painting probes for human chromosomes 3,7,8,13,17 and 21 and X and the probe pHY2.1 for the Y chromosome coupled with fluorescent in situ hybridization (FISH) analysis, the distribution of chromosomes is reported in nuclei of Sertoli cells of the adult testis and in stimulated blood lymphocytes. The distribution of chromosomes in the two cell types is significantly different. A strong tendency for each pair of homologues to pair is inferred from the observation of only a single detectable signal in the majority of Sertoli cell nuclei. The sex chromosomes, by contrast, give two clearly separated signals. Interphase nuclei in dividing blood lymphocytes, analysed as controls, also show mainly two separated signals for all non-acrocentric autosomal pairs, but acrocentric pairs no. 13 and 21 show some tendency to associate, probably reflecting satellite association.

Adult↗
PubMed1995

A reassessment of Y chromosomal behaviour in germ cells and Sertoli cells of the mouse as revealed by in situ hybridisation.

In situ hybridisation experiments were carried out to reappraise the state of condensation of the Y chromosome in germ cells and Sertoli cells of the mouse. Previous work had suggested that all testicular cells showed a condensed Y chromosome prior to the adult stage. We now demonstrate that, although the Y chromosome is condensed in pre-pubertal Sertoli cells, it is greatly expanded in primordial germ cells (gonocytes). An expanded Y-signal is first seen in Sertoli cell nuclei at or around day 21 of postnatal development, coinciding with the first appearance of spermatids in the germinal epithelium.

Animals↗
PubMed1994

Condensation behaviour of the human X chromosome in male germ cells and Sertoli cells examined by fluorescence in situ hybridization.

The chromatin condensation behaviour of the human X chromosome has been studied by fluorescence in situ hybridization (FISH) analysis in germ cells and Sertoli cells of the adult testis, and comparisons are made with previous findings for the human Y chromosome and for chromosome 7. In meiotic prophase, the X chromosome can be seen to extend greatly at zygotene and to contract through pachytene into the sex vesicle. Such extension, which has also been noted for the human Y chromosome at this stage of meiosis, could be a prerequisite for XY pairing and crossing-over. By in situ hybridization analysis, the sex chromosomes of patients with 'Sertoli-cell-only' syndrome appear extremely contracted compared with the normally extended state of those in adult Sertoli cells of fertile men. By contrast, the state of expansion for chromosome 7 in Sertoli cells appears identical for sterile and fertile testes. This could suggest an association between gene-controlled germ cell losses and failure of expansion of the sex chromosome axes. The variable patterns of extension and contraction for the X and Y chromosome axes in germ cells and Sertoli cells might provide underlying clues to patterns of expression noted for sex-linked genes in the human testis.

Adult↗
PubMed1993

A Y chromosome gene family with RNA-binding protein homology: candidates for the azoospermia factor AZF controlling human spermatogenesis.

We have previously mapped the human azoospermia factor to a deletion in Y chromosome interval 6 (subinterval XII-XIV). We now report the isolation and characterization of a gene family located within this deletion. Analysis of the predicted protein products suggests a possible role in RNA processing or translational control during early spermatogenesis. The Y chromosome RNA recognition motif (YRRM) family includes a minimum of three members expressed specifically in the testis. Interphase in situ results and Southern blot analysis indicate that several further YRRM sequences map within interval 6. Several mammalian species show Y chromosome conservation of YRRM sequences. We have detected deletions of YRRM sequences in two oligospermic patients with no previously detectable mutation.

Amino Acid Sequence↗
PubMed1993

Chromatin condensation behaviour of the Y chromosome in the human testis. I. Evidence for decondensation of distal Yq in germ cells prior to puberty with a switch to Sertoli cells in adults.

The condensation behaviour of the human Y chromosome in germ cells and Sertoli cells of pre- and post-pubertal testes was followed by fluorescence in situ hybridisation using probes for three different regions of the Y chromosome. Patterns of expansion or contraction of signal are taken to reflect degrees of condensation of the related Y chromatin and hence its potential for genetic activity. For probe pHY2.1, which labels the distal non-fluorescent and fluorescent heterochromatin of the Y chromosome (Yq12), an expanded signal seen in gonocytes of the prepubertal testis is superseded by a condensed signal seen in adult germ cells at all but the zygotene stage of meiotic prophase when meiotic pairing takes place. In contrast, Sertoli cells show a condensed signal pre-pubertally but a greatly expanded signal in the adult testis. A totally condensed pHY2.1 signal is found in a chromosomally normal man with Sertoli-cell-only syndrome. It is hypothesised that control over at least some facets of spermatogenesis may not, in the adult, be autonomous to the germ cells, but rather may emanate from the Sertoli cells. Chromatin expansion at zygotene could, however, be important for pairing and crossing over in the XY bivalent, successful synapsis ensuring survival of spermatocytes into the post-meiotic stages.

Adult↗
PubMed1992

Infertility in human males with autosomal translocations. II. Meiotic studies in three reciprocal rearrangements, one showing tertiary monosomy in a 45-chromosome individual and his father.

The meiotic prophase behavior of three human reciprocal autosomal translocations is presented. Each translocation was ascertained among men attending an infertility clinic. Two involved chromosomes 3 and 5, with breakpoints in different places. Quadrivalents were seen in every cell. The third translocation was a rare t(11q;15q) rearrangement in a 45-chromosome individual with tertiary monosomy. The long product of the translocation was retained in the karyotype over two generations of the family, the short product having been lost. At meiotic prophase, a trivalent was seen in every cell; in 60% of the nuclei, the short arm of the trivalent was closely associated with the XY bivalent. The transmission and phenotypic effects of tertiary monosomy in man and the mouse are discussed.

Chromosome Deletion↗
PubMed1992

Role of the pseudoautosomal region in sex-chromosome pairing during male meiosis: meiotic studies in a man with a deletion of distal Xp.

Meiotic studies were undertaken in a 24-year-old male patient with short stature, chondrodysplasia punctata, ichthyosis, steroid sulfatase deficiency, and mild mental retardation with an inherited cytologically visible deletion of distal Xp. Molecular investigations showed that the pseudoautosomal region as well as the steroid sulfatase gene were deleted, but telomeric sequences were present at the pter on the deleted X chromosome. A complete failure of sex-chromosome pairing was observed in the primary spermatocytes of the patient. Telomeric approaches between the sex chromosomes were made at zygotene in some cells, but no XY synaptonemal complex was formed. The sex chromosomes were present as univalents at metaphase I, and germ-cell development was arrested between metaphase I and metaphase II in the vast majority of cells, consistent with the azoospermia observed in the patient. The failure of XY pairing in this individual indicates that the pseudoautosomal sequences play an important role in initiating XY pairing and formation of synaptonemal complex at meiosis.

Adult↗
PubMed1991

Persistence of two Y chromosomes through meiotic prophase and metaphase I in an XYY man.

Studies of spermatogenesis in an XYY male, presenting at a subfertility clinic, confirm the tendency for the germ cells to lose the second Y chromosome but for some XYY cells to reach metaphase I (MI). Light microscope studies of MI revealed the presence of YY bivalents and EM studies of microspread, silver-stained pachytene stages showed 30% of the cells to have two Y chromosomes; 13 out of 16 of these showing a YY synaptonemal complex. Strikingly, the Y axes show only partial synapsis; in no case was synapsis of the long arm heterochromatic regions apparent.

Humans↗
PubMed1990

Infertility in human males with autosomal translocations: meiotic study of a 14;22 Robertsonian translocation.

Pachytene analysis was undertaken in a male patient heterozygous for a 14q22q Robertsonian translocation. The relatively low rate of XY autosome association led us to examine the relationships existing between the chromosomes involved in the translocation, the rate of XY-autosome association and the degree of spermatogenic failure. Cytogenetic investigations in infertile men and the results of the meiotic studies suggest a direct correlation between the frequency of XY-autosome association at pachytene and the degree of spermatogenic failure. Whether associations arise as a consequence or cause of germ cell failure is still not certain.

Adult↗
PubMed1990

Prophase of meiosis in human spermatocytes analysed by EM microspreading in infertile men and their controls and comparisons with human oocytes.

Observations at the electron microscope (EM) level have been made on 1883 primary spermatocytes from 40 chromosomally normal subfertile men and 566 spermatocytes from 10 fertile controls, using the technique of microspreading. Spermatocytes of infertile men in general showed greater indications of degeneration including higher levels of background silver deposition, nucleolar organising region - XY associations, fragmentation of synaptonemal complexes and overproduction of XY excrescences. A few oligospermic men also showed an immature morphology of the XY pair and/or a reduced extent of XY synapsis. Dissociation of the sex chromosome axes at prophase was found to occur with a much lower frequency than that recorded for separated X and Y chromosomes at metaphase I. In a single spermatocyte, synaptonemal complex formation was observed between Xqter and Yqter, a situation that could enable rare XqYq interchange. A proteinaceous stalked body exists on the Y axis towards its non-pairing end; this structure might have a functional relationship with the gene for spermatogenesis, (AZF), located at the euchromatin/heterochromatin interface. Compared with human oocytes, spermatocytes show fewer anomalies of synapsis, i.e. asynapsed segments or whole axes, non-homologous associations, interchanges, interlocks. These latter data agree well with findings from the mouse.

Adult↗