Biomedical subjects

B M Cattanach

Publications and source records attributed to B M Cattanach.

At least 37 records · Page 2Linked to original sources

PubMed1994

Genetic imprinting in the mouse: implications for gene regulation.

Genetic imprinting specifies a germline marking that subsequently results in the repression of one or other parental allele at some point in development. Genetic manipulations to generate maternal and paternal duplications of specific chromosome regions have been used to screen almost the entire mouse genome for evidence of imprinting. As a result, 15 imprinting effects involving 10 regions on 6 different chromosomes have been detected that range from early embryonic lethalities to various growth and developmental defects seen only after birth. Genes with important roles in development therefore appear to be involved. Diverse studies have identified four imprinted genes, all of which show monoallelic expression in some, but not necessarily all, tissues. A correlation with methylation is indicated but the pattern of methylation is not consistent for each of the genes; methylation is therefore unlikely to be the imprinting signal. Methods being used to identify further imprinted genes are summarized and some of the difficulties posed are indicated.

Animals↗

PubMed1993

Parental-origin-specific epigenetic modification of the mouse H19 gene.

The H19 gene produces an abundant developmentally regulated transcript of unknown function in normal embryos. In the mouse it lies on chromosome 7 and is subject to transcriptional regulation by parental imprinting, which results in the maternally inherited gene being expressed and the paternally inherited gene being repressed. Embryos carrying maternal duplication/paternal deficiency for distal chromosome 7 (MatDi7) therefore express a double dose of H19. Here we examine the parental-origin-specific epigenetic modifications that may be involved in this regulation by comparing CpG methylation and nuclease sensitivity of chromatin in MatDi7 embryos with normal littermates. We show that specific sites in the CpG island promoter and 5' portion of the gene are methylated only on the paternal allele. Furthermore, active maternal alleles in chromatin of MatDi7 embryos are more sensitive and accessible to nucleases. Therefore hypermethylation and chromatin compaction in the region of the H19 promoter is associated with repression of the paternally inherited copy of the gene. Most, but not all, of these sites are unmethylated in sperm, with methylation of the paternal promoter occurring after fertilization. These results contrast with our findings for the closely linked and reciprocally imprinted gene encoding insulin-like growth factor II (ref. 4).

Animals↗

PubMed1993

Mapping the murine Xce locus with (CA)n repeats.

The X Chromosome (Chr) controlling element locus (Xce) in the mouse has been shown to influence the X inactivation process. Xce maps to the central region of the X Chr, which also contains the Xist sequence, itself possibly implicated in the X inactivation process. Three microsatellite markers spanning the Xist locus have been isolated from an Xist containing YAC. All three microsatellite markers showed complete linkage with Xce in recombinants for the central span of the mouse X Chr between Ta and Moblo and strong linkage disequilibrium with Xce in all but one of the inbred mouse strains tested. In the standard Xceb typing strain JU/Ct, the two microsatellites most closely flanking Xist fail to carry the allelic forms expected if Xist and Xce are synonymous. Alternative explanations for this finding are presented in the context of our search for understanding the relation between Xist and Xce.

Animals↗

PubMed1993

The radiosensitivity of spermatogonial stem cells in C3H/101 F1 hybrid mice.

The radiosensitivity of spermatogonial stem cells of C3H/HeH x 101/H F1 hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIIirr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D0 of 1.4 Gy. In stages XIirr-Virr, when the cells were proliferatively active, the D0 was about 2.6 Gy. Based on the D0 values for sensitive and resistant spermatogonia and on the D0 for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing. When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = e tau D, with tau = 1 for the sensitive and tau = 0.1 for the resistant spermatogonial stem cells, with a maximal e tau D of 100.

Animals↗

PubMed1993

Large deletions and other gross forms of chromosome imbalance compatible with viability and fertility in the mouse.

Large deletions and other gross forms of chromosome imbalance are known in man but have rarely been found in the mouse. By screening progeny of spermatogonially irradiated male mice for a combination of runting and other phenotypic effects, we have identified animals that have large deletions comprising from 2.5-30 percent of the length of individual chromosomes, or other major chromosome changes, which are compatible with viability and fertility. Certain chromosome regions appear particularly susceptible to the generation of viable deletions and this has implications for radiation mutagenesis studies. Correlations with human deletions are also indicated.

Animals↗

PubMed1993

Deletion of Y chromosome sequences located outside the testis determining region can cause XY female sex reversal.

An approach designed to map and generate mutations in the region of the short arm of the mouse Y chromosome, known to be involved in sex determination and spermatogenesis, is described. This relies on homologous Yp-Sxra pairing and asymmetrical exchange which can occur at meiosis in XY males carrying Sxra on their X chromosome. Such exchange potentially generates deficiencies and duplications of Yp or Sxra. Three fertile XY females were found out of about 450 XY offspring from XSxra/Y x XX crosses. In all three, despite evidence for deletion of Y chromosomal material, the Sry locus was intact. Each deletion involved a repeat sequence, Sx1, located at a distance from Sry. Since expression of Sry was affected these results suggest that long range position effects have disrupted Sry action.

Animals↗

PubMed1993

Activation of an imprinted Igf 2 gene in mouse somatic cell cultures.

The mouse insulin-like growth factor II gene (Igf 2), located on distal chromosome 7, is parentally imprinted such that the paternal allele is expressed while the maternal allele is transcriptionally silent. We derived a cell line from a mouse embryo maternally disomic and paternally deficient for distal chromosome 7 (MatDi7) to determine the stability of gene repression in culture. MatDi7 cells maintained Igf2 in a repressed state even after immortalization, except for one randomly picked clone which spontaneously expressed the gene. Igf 2 was expressed in a cell culture derived from a normal littermate; this expression was growth regulated, with Igf 2 mRNA levels increasing in the stationary phase of growth. Analysis of the methylation status of 28 sites distributed over 10 kb of the gene did not show consistent differences associated with expression level in the normal and MatDi7 cell lines, and the CpG island in the Igf 2 promoter remained unmethylated in all of the cell lines. Only with an oncogenically transformed cell line did the promoter become extensively methylated. We attempted to derepress the imprinted gene in MatDi7 cells by treatments known to alter gene expression. Expression of the Igf 2 allele in MatDi7 cells was increased in a dose-dependent manner by treatment with 5-aza-2'-deoxycytidine or bromodeoxyuridine, agents known to change DNA methylation patterns or chromatin conformation. Treatment of the cells with 1-beta-D-arabinofuranosylcytosine, 2'-deoxycytidine, calcium ionophore, heat shock, cold shock, or sodium butyrate did not result in increases in the levels of Igf 2 expression. It seems likely that the mechanism of the Igf 2 imprint involves subtle changes in the methylation or chromatin conformation of the gene which are affected by 5-aza-2'-deoxycytidine and bromodeoxyuridine.

Animals↗

PubMed1992

The response of spontaneous and transplantable murine tumors to vasoactive agents measured by 31P magnetic resonance spectroscopy.

31P magnetic resonance spectroscopy has been used to compare the effects of the vasoactive agents hydralazine and flunarizine on the oxygenation of the transplantable tumors, SCCVII/Ha and 16C, and a range of spontaneous mammary tumors arising in the breeding stock in the Genetics Division at the Radiobiology Unit. The vasodilator hydralazine, previously shown to increase the radiobiological hypoxic fraction of transplantable murine tumors, increased inorganic phosphate to total phosphate (Pi/total) in SCCVII/Ha and 16C tumors. However, only two spontaneous tumors responded to this agent (2/12). The calcium antagonist flunarizine, which sensitizes the SCCVII tumor to X rays, consistent with a reduction in hypoxic fraction, reduced Pi/total in this and the 16C tumor. Further, most spontaneous tumors tested (8/10) responded to this agent, as measured by a reduction in Pi/total. These results point to fundamental differences between transplantable and spontaneously arising tumors in mice in their response to vasoactive agents.

Animals↗

PubMed1992

A candidate mouse model for Prader-Willi syndrome which shows an absence of Snrpn expression.

The best examples of imprinting in humans are provided by the Angelman and Prader-Willi syndromes (AS and PWS) which are associated with maternal and paternal 15q11-13 deletions, respectively, and also with paternal and maternal disomy 15. The region of the deletions has homology with a central part of mouse chromosome 7, incompletely tested for imprinting effects. Here, we report that maternal duplication for this region causes a murine imprinting effect which may correspond to PWS. Paternal duplication was not associated with any detectable effect that might correspond with AS. Gene expression studies established that Snrpn is not expressed in mice with the maternal duplication and suggest that the closely-linked Gabrb-3 locus is not subject to imprinting. Finally, an additional new imprinting effect is described.

Animals↗

PubMed1991

Embryological and molecular investigations of parental imprinting on mouse chromosome 7.

Mouse embryos with duplications of whole maternal (parthenogenetic and gynogenetic) or paternal (androgenetic) genomes show reciprocal phenotypes and do not develop to term. Genetic complementation has identified the distal region of chromosome 7 (Chr 7) as one of the regions for which both a maternal and paternal chromosome copy are essential for normal development, presumably because of the presence of imprinted genes whose expression is dependent on their parental origin. Embryos with the maternal duplication and paternal deficiency of distal Chr 7 are growth retarded and die around day 16 of gestation; the reciprocal paternal duplication embryos die at an unidentified earlier stage. We report here the incorporation of cells with the paternal duplication into chimaeras, resulting in a striking growth enhancement of the embryos. One gene located on mouse distal Chr 7 (ref. 5) is the insulin-like growth factor 2 (Igf2) gene, an embryonic mitogen. In embryos with the maternal duplication of distal Chr 7, the two maternal alleles of the Igf2 gene are repressed. The presence of two paternal alleles of this gene in many cells is probably responsible for the growth enhancement observed in chimaeras. We propose that there are other imprinted genes in this Chr 7 region. We also compare the imprinting of this subgenomic region with phenotypes resulting from the duplication of the whole parental genome in parthenogenones and androgenones.

Actins↗

PubMed1991

Molecular genetic analysis of the Ta25H deletion: evidence for additional deleted loci.

Seventeen linking clones sublocalized to the central region of the mouse X Chromosome (Chr) were screened against genomic DNA from male mice carrying the tabby-25H (Ta25H) deletion. Two of these linking clones, lambda EM131 and lambda EM169, were found to be deleted in Ta25H/Y animals. Genetic mapping through Mus musculus domesticus/Mus spretus interspecific backcross progeny, segregating for the original tabby (Ta) gene mutation, was utilized to order these markers and to define nearest flanking markers to the Ta25H deletion (lambda EM140 and lambda EM171). The size of the Ta25H deletion was thus estimated as up to 4.5 centiMorgans (cM). The order of markers, proximal to distal, was found to be lambda EM140/lambda EM131, mouse androgen receptor gene (Ar)/lambda EM169, Ta/lambda EM171. A putative CpG-rich island and a highly evolutionarily conserved DNA probe were isolated from the DXCrc169 locus which co-segregates with the Ta locus in this study.

Animals↗

PubMed1991

Testicular steroidogenesis in X/X sex-reversed mice.

The sex-reversed X/X Sxr mouse is phenotypically male but lacks germ cells. This provides the opportunity to examine Leydig cell function in the absence of a normal germinal epithelium and without experimental manipulation of the testis. Serum testosterone was lower in Sxr males compared to normal (X/Y) males but there was no significant difference in intratesticular testosterone levels. Serum immunoactive and bioactive luteinizing hormone levels were not significantly different between the two groups. Injection of human chorionic gonadotrophin (hCG) increased intratesticular testosterone in Sxr males more than in normal males although there was no difference in serum testosterone levels. These differences in circulating and intratesticular testosterone levels may be related to reduced blood flow through the Sxr testis. Both basal and hCG-stimulated androgen production by whole testes in vitro were not significantly different between normal and Sxr males. Androgen production per Leydig cell, however, was significantly reduced in cells from Sxr males; this difference was apparent under basal conditions and following stimulation with hCG, dibutyryl cyclic AMP, 22R-hydroxycholesterol or pregnenolone. Results show that in the absence of a normal germinal epithelium there is a decrease in the steroidogenic capacity of the Leydig cells although steroidogenesis by the whole testis is not impaired significantly.

Androgens↗

PubMed1991

Rumpshaker: an X-linked mutation affecting CNS myelination. A study of the female heterozygote.

This study examines the myelin deficits found in the spinal cord and optic nerves of female mice heterozygotes for rumpshaker (rsh), an X-linked mutation causing hypomyelination. No clinical abnormalities were detected but morphological changes were evident, particularly in the spinal cord, which showed no evidence of resolving with age. In the spinal cord, scattered hypomyelinated axons, occasionally grouped in twos or threes, were the major feature; oligodendrocyte numbers were slightly elevated at all ages compared to normal male littermates and the total amount of myelin was reduced. Myelin protein composition of the sheaths was examined by immunostaining for myelin basic protein (MBP) and two peptide regions of PLP/DM-20 molecule; one being proteolipid protein (PLP)-specific and the other recognizing the c-terminal common to PLP-DM-20. The majority of myelin sheaths immunostained for MBP and PLP. Occasional MBP-positive sheaths failed to stain with PLP/DM-20 or PLP-specific antiserum. Therefore, at least two types of immunocytochemically-defined myelin sheaths are present in the heterozygotes. Changes in the optic nerves were much less obvious; glial cell numbers were increased but thinly myelinated axons were not detected although the total amount of myelin was reduced compared to normal littermates. In no instance were mosaic, amyelinated/hypomyelinated patches detected. Heterozygotes for rsh, therefore, are considerably different from those for other X-linked myelin mutations like the jimpy mouse and the myelin-deficient rat, both in regard to the severity of the lesions and their failure to recover with age.

Animals↗

PubMed1991

Genetic and molecular evidence of an X-chromosome deletion spanning the tabby (Ta) and testicular feminization (Tfm) loci in the mouse.

A new radiation-induced mutation in the mouse, tabby-25H (Ta25H), has proved to be a deletion which spans both the tabby and testicular feminization (Tfm) loci on the X chromosome. The Ta phenotype closely resembles that of the original TaFa mutation in both the heterozygous and hemizygous conditions but Ta25H/Y animals additionally show the Tfm/Y phenotype, being externally female but possessing abdominally located testes. There is a shortage of both Ta25H/+ and Ta25H/Y classes relative to their normal sibs among the progeny of Ta25H/+ females at weaning age and this was indicated to be due to prenatal or neonatal losses. Exencephaly was observed in some members of both classes prior to birth. Both Ta25H classes tend to be runted at weaning but, remarkably, Ta25H/+ females often show a range of abnormalities not evident in Ta25H/Y animals. When probes for the Zfx, Ccg-1, Phk, and DXPas19 loci, which lie close to Ta, were hybridised to DNAs from Ta25H hemizygotes, the profiles of the X-linked bands were similar to those of control DNAs, suggesting these loci lie outside the deletion. However, a clear absence of an X-linked band was found with human androgen receptor probes, indicating that the Tfm locus is indeed missing. The deletion, therefore, extends a minimum of 1.5 cM and, with its proximal and distal boundaries partially defined, it could be as large as 4 cM. As Ta25H/+ females show the striped X-inactivation coat pattern, the putative X-inactivation centre, Xce, which lies close to Ta, cannot be located within the region deleted. The greasy (Gs) locus similarly appears to lie outside the deletion.

Androgen-Insensitivity Syndrome↗

PubMed1990

Rumpshaker mouse: a new X-linked mutation affecting myelination: evidence for a defect in PLP expression.

This report describes a new X-linked mutation in mice, named rumpshaker (rsh) which is associated with hypomyelination of the central nervous system. Myelination commences appropriately but the majority of sheaths fail to develop normally. Oligodendrocytes are increased in number and have prominent Golgi apparatus, rough endoplasmic reticulum and free ribosomes. Occasional cisternae of rough endoplasmic reticulum are distended. Some dense lamellar inclusions occur in oligodendrocytes but overall, degenerative changes and cell death are uncommon. Immunostaining demonstrates a major defect in expression of PLP DM-20. Using site-specific antisera directed at different portions of the PLP/DM-20 molecule, the major defect appears to be with PLP where virtually no myelin sheaths are positive. Antiserum against the C-terminal common to PLP and DM-20 shows reduced but definite myelin staining. Genetic analysis indicates a locus at or close to the PLP/jimpy (jp) locus. The rsh mutation, however, differs from jp in that affected mice have normal longevity, can breed, produce substantially more myelin and have increased numbers of oligodendrocytes.

Animals↗

PubMed1990

Autosomal and X-chromosome imprinting.

Mouse genetic studies using Robertsonian and reciprocal translocations have shown that certain autosomal regions of loci are subject to a parental germ line imprint, which renders maternal and paternal copies functionally inequivalent in the embryo or later stages of development. Duplication of maternal or paternal copies with corresponding paternal/maternal deficiencies in chromosomally balanced zygotes causes various effects. These range from early embryonic lethalities through to mid-fetal and neonatal lethalities, and in some instances viable young with phenotypic effects are obtained. Eight to nine chromosomal regions that give such imprinting effects have been identified. Six to seven of these regions are located in only three chromosomes (2, 7 and 17). The two other regions are located in chromosomes 6 and 11. Maternal and paternal disomies for each of four other chromosomes (1, 5, 9 and 14) have been recovered with different frequencies, but the possibility that this may be due to imprinting has yet to be supported by follow-up studies on regions of the chromosomes concerned. No clear evidence of genetic-background modifications of the imprinting process have been observed in these mouse genetic experiments. The mammalian X chromosome is also subject to imprinting, as demonstrated by the non-random, paternal X-inactivation in female mouse extra-embryonic tissues and in the somatic cells of marsupial females. There is also the opposite bias towards inactivation of the maternal X in the somatic cells of female mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Sex chromosome pairing patterns in male mice of novel Sxr genotypes.

The influence of the sex-reversal factor (Sxr) on X and Y chromosome pairing was examined by comparing males with "novel" and "standard" Sxr genotypes. The novel Sxr males were exceptional in carrying Sxr on their X rather than their Y chromosome, or homozygously on both their X and Y chromosomes, or on a Y chromosome of different origin to that on which the factor arose. Regardless of its chromosomal location, Sxr was found to elevate the frequency of X-Y separation. Univalent X and Y chromosomes were observed to undergo self-association in a variable proportion of spermatocytes of all Sxr-carrying males. There was a suggestion that chromosomal location of the factor could influence the frequency of univalent self-association. Our observations do not support the published hypothesis of Y self-pairing as the cause of the elevated rate of X-Y separation at pachytene in Sxr-carrying males. Rather, they suggest that heterozygosity due to the presence of Sxr in the XY pairing region may be sufficient to disrupt pairing and cause univalence, or alternatively, that Sxr is an inefficient promoter of X-Y pairing initiation.

Animals↗

PubMed1989

Induction of specific locus mutations in mouse spermatogonial stem cells by combined chemical X-ray treatments.

Data that demonstrate how the biology of spermatogenesis plays an important role in determining the yield of genetic damage from ionizing radiation are briefly reviewed. It is suggested that for valid extrapolations of data from mouse mutation experiments to man detailed knowledge of the spermatogonial stem cell systems in the two species is required. Two new sets of mouse specific mutation data are presented. (1) When a 2 mg/kg dose of triethylenemelamine (TEM) was used as a conditioning dose and followed 24 h later by 6 Gy X-rays, the mutation yield from spermatogonial stem cells was over twice as high (30.20 X 10(-5)/locus/gamete) as that when the X-ray dose was given alone (13.75 X 10(-5)/locus/gamete). No such effect was found when the TEM was given only 3 h prior to the X-irradiation. Since TEM at the dose used is inefficient at inducing specific-locus mutations, an augmentation of the X-ray response is indicated. It has therefore been concluded that the augmented mutation responses obtained with equal 24 h X-ray fractionations at high doses are attributable to mutation induction by the second dose. The responsive cells would be the formerly resistant component of the stem cell population that had survived the TEM treatment and that had been 'triggered' into a radiosensitive phase by the population depletion. (2) When 2 doses of 500 mg/kg hydroxyurea (HU) were given 3 h apart 3 h prior to 6 Gy X-rays to reduce the numbers of stem cells in the S and G2 phases of the cell cycle exposed to the radiation, the mutation responses was greatly enhanced to a level that is the highest yet recorded per unit X-ray dose (7.10 X 10(-5)/locus/gamete/Gy). No such effect was obtained when the intervals between the HU and X-ray treatments were either shorter (less than 0.5 h) or longer (24 h). It was concluded that X-ray-induced specific-locus mutations derive principally from stem cells in the G1 phase of the cell cycle. The reasons why the X-ray-induced mutation-yields from repopulating stem cells (with a short cell cycle and, hence, short G1 phase) are similar to those from undamaged stem cell populations, in contrast to translocation yields, therefore remains unresolved.

Animals↗