Showing papers on "X chromosome published in 1981"
TL;DR: Since 5-azacytidine treatment results in hypomethylation of DNA, DNA methylation may be a mechanism of human X chromosome inactivation.
Abstract: A mouse-human somatic cell hybrid clone, deficient in hypoxanthine-guanine phosphoribosyltransferase (HPRT) and containing a structurally normal inactive human X chromosome, was isolated. The hybrid cells were treated with 5-azacytidine and tested for the reactivation and expression of human X-linked genes. The frequency of HPRT-positives clones after 5-azacytidine treatment was 1000-fold greater than that observed in untreated hybrid cells. Fourteen independent HPRT-positive clones were isolated and analyzed for the expression of human X markers. Isoelectric focusing showed that the HPRT expressed in these clones is human. One of the 14 clones expressed human glucose-6-phosphate dehydrogenase and another expressed human phosphoglycerate kinase. Since 5-azacytidine treatment results in hypomethylation of DNA, DNA methylation may be a mechanism of human X chromosome inactivation.
671 citations
TL;DR: Fragments from section 3 of the salivary gland X chromosome of D. melanogaster were dissected with a micromanipulator and a sample of which were analysed and shown to contain Drosophila DNA which hybridises in situ to the region of section 2 of the X chromosome.
Abstract: Fragments from section 3 of the salivary gland X chromosome of D. melanogaster were dissected with a micromanipulator. The DNA was extracted, cut and ligated to a λ vector in a volume of a few nanoliters in an oil chamber monitored through a microscope. From about 10 pg of DNA we obtained 80 recombinant clones, a sample of which were analysed and shown to contain Drosophila DNA which hybridises in situ to the region of section 3 of the X chromosome. With this technique we can isolate clones from any desired region as small as 200 kb from the euchromatic arms of polytene chromosomes.
298 citations
TL;DR: A library of 50,000 recombinants representative of the human X chromosome has been constructed for the investigation of genetic diseases such as Duchenne muscular dystrophy and of neoplasia, where several specific chromosomal anomalies have been identified.
Abstract: A library of 50,000 recombinants representative of the human X chromosome has been constructed. Human X chromosomes were physically separated using a fluorescence-activated cell sorter. The DNA was purified from the chromosomes, digested to completion with the restriction enzyme EcoRI and cloned into the phage lambda gtWES.lambda B. The X-derived nature of the recombinants was confirmed by hybridization to rodent/human cell line DNA containing only the human X chromosome. Such libraries will be particularly useful for the investigation of genetic diseases such as Duchenne muscular dystrophy, where the basic defect has not been elucidated, and of neoplasia, where several specific chromosomal anomalies, particularly for the leukaemias, have been identified.
234 citations
TL;DR: A model of amplification in which additional rounds of replication are specifically initiated within the central gene-containing regions, followed by bidirectional replication in the absence of discrete termination sites is suggested.
232 citations
TL;DR: A cycle of inactivation and reactivation of one X chromosome in the female (XX) germ line is shown by analysis of gene dosage effects on activity of an X-linked enzyme.
Abstract: A cycle of inactivation and reactivation of one X chromosome in the female (XX) germ line is shown by analysis of gene dosage effects on activity of an X-linked enzyme. The ratio of activities of the X-linked enzyme HPRT and an autosomal enzyme APRT are determined in XX and XY germ cells from embryonic gonads from the 12th to the 17th day of pregnancy. Mitotic stages of XX and XY germ cells on the 12th day have similar HPRT:APRT ratios, but on the 13th day the ratios are significantly higher in XX than XY germ cells. As the XX germ cells enter meiosis they show a marked increase in HPRT:APRT ratio which is primarily due to a rise in X-linked HPRT activity. Comparisons are made with XO germ cells on the 12th and 14th day. On the 12th day, XO do not differ from XX and XY germ cells, suggesting that only one X chromosome is active in XX germ cells at this stage. On the 14th day, on the other hand, the HPRT:APRT ratios in XO and XY germ cells are similar but in XX germ cells the ratio is significantly higher. The twofold difference between the ratio in XX and XO germ cells suggests that by this stage both X chromosomes are active in XX germ cells. The subsequent large increase of the ratio in XX relative to XY germ cells is thought to reflect their differing cell states.
229 citations
TL;DR: Many of the data are consistent with the hypothesis that XX males arise through interchange of the testic-determining gene on the Y chromosome and a portion of the X chromosome containing the Xg gene, but actual evidence in favor of this hypothesis is still lacking, and the H-Y antigen data are not easy to explain.
Abstract: Information relating to the etiology of human XX males is reviewed. The lesser body height and smaller tooth size in comparison with control males and first-degree male relatives could imply that the patients never had any Y chromosome. Neither reports of occasional mitoses with a Y chromosome, nor of the occurrence of Y chromatin in Sertoli cells are convincing enough to support the idea that low-grade or circumscribed mosaicism is a common etiologic factor. Reports of an increase in length of one of the X chromosomes in XX males are few and some are conflicting. Nor is there any evidence to support the idea of loss of material. However, absence of visible cytogenetic alteration does not rule out the possibility of translocations, exchanges or deletions.
212 citations
Journal Article•
TL;DR: It is concluded that the locus for Duchenne muscular dystrophy is at Xp21 and, furthermore, that this site may be particularly susceptible both to chromosome breakage and exchange and to gene mutation.
Abstract: An isolated case of Duchenne muscular dystrophy in a female who has a de novo t(X;5)(p21;q35) translocation is described. The similarities between this patient and four previously reported females with Duchenne muscular dystrophy are discussed. It is concluded that the locus for Duchenne muscular dystrophy is at Xp21 and, furthermore, that this site may be particularly susceptible both to chromosome breakage and exchange and to gene mutation.
143 citations
TL;DR: The lack of complementation indicates that the X chromosome-linked mutations in mouse and man affect homologous loci and supports the evolutionary conservation of X chromosomal loci in mammals; however, the position of the locus on the human X chromosome indicates that intrachromosomal rearrangement has occurred.
Abstract: We have established a cell line from mouse kidney cells expressing the tfm mutation and showed that these cells lack androgen binding activity. A subclone of these simian virus 40 (SV40)-transformed cells (6TGR-SV-tfm) selected in 6-thioguanine and lacking hypoxanthine phosphoribosyltransferase was used to produce a series of mouse--human hybrids containing the normal human X chromosome or various X autosome-translocation chromosomes (expressing only segments of the human X chromosome). When the androgen receptor locus (AR) was present in the hybrid, the number of receptor sites and kinetics of binding were similar to that in the human parental cells. Analysis of hybrids with partial human X chromosomes by using assays for X chromosome-linked enzymes and for the androgen receptor protein indicate that the AR locus on the human X chromosome is near the centromere between Xq13 and Xp11 and is proximal to the locus for phosphoglycerate kinase. Hybrids derived from 6TGR-SV-tfm mouse cells and human labial fibroblasts from an XY individual with the ar- form of androgen insensitivity have no binding activity. The lack of complementation indicates that the X chromosome-linked mutations in mouse and man affect homologous loci and supports the evolutionary conservation of X chromosomal loci in mammals; however, the position of the locus on the human X chromosome indicates that intrachromosomal rearrangement has occurred.
135 citations
Journal Article•
TL;DR: The present results suggest that the influence of the X- and Y-chromosome gene(s) on amelogenesis is the same in quantitative terms but different in relation to the determination of the distance between dentino-enamel junctions; the Y chromosome is more effective than the X chromosome in that respect.
Abstract: Enamel thicknesses in 45,X females', their male and female relatives', and population control males' and females' permanent tooth crowns were determined from radiographs. The results showed that the enamel layer in both maxillary first incisors and canines of 45,X females is definitely thinner than that of control males or females. Enamel in control males' and females' teeth was about equal in size. The distance between mesial and distal dentino-enamel junctions or the thickness of "dentin" was similar in 45,X females' and in control females' teeth, but definitely smaller than in control males' teeth. These findings show that in the presence of the second sex-chromosome in the chromosome complement, whether X or Y, there is a definite and equal increase in the amount of enamel. On the other hand, in the presence of the Y chromosome in the chromosome complement, relative to the second X chromosome, there is a definite increase in the thickness of the dentin. The results of earlier studies have indicated a direct growth-promoting effect of the sex chromosomes on tooth growth, and that the effect of X and Y chromosomes is different. The present results suggest that the influence of the X- and Y-chromosome gene(s) on amelogenesis is the same in quantitative terms but different in relation to the determination of the distance between dentino-enamel junctions; the Y chromosome is more effective than the X chromosome in that respect. It is postulated that this size-increasing effect of the Y-chromosome gene(s) might result from its profound effect on cell proliferations.
129 citations
TL;DR: The results have been interpreted to mean that the non-random X expression derives from a primary non- randomness of the X inactivation process and that a new and more extreme Xce allele, designated Xce c , was present on the Pgr-1 a -marked X chromosome.
Abstract: The non-random X chromosome expression that has been observed with coat markers in female mice heterozygous for the Xce alleles, Xcea and Xceb, has now been investigated with the electrophoretic enzyme marker, Pgk-1. Because the Xce status of the Pgk-1a marked chromosome was not known, PGK expression was assessed in Pgk-1a/Pgk-lb heterozygotes which carried either Xcea or Xceb on their Pgk-1b chromosome. The PGK-1A allozyme was found to predominate in both genotypes but when Xceb was present on the Pgk-lb chromosome the expression of the two allo-zymes was less unequal. This effect was seen in both liver and kidney of adults and to at least the same degree in embryos aged 13·5 and 7·5 days. The results have been interpreted to mean that the non-random X expression derives from a primary non-randomness of the X inactivation process and that a new and more extreme Xce allele, designated Xcec, was present on the Pgr-1a-marked X chromosome.
113 citations
TL;DR: The assumption that there is no dosage compensation for Z-linked or X-linked genes by the sex chromosome inactivation mechanism in the sex chromosomes of Amphibia is supported.
Abstract: A modified BrdU-Hoechst-Giemsa technique permitted the demonstration of easily reproducible replication patterns in the somatic chromosomes of Amphibia. These banding patterns allow for the first time a precise identification of all chromosomes and the analysis of the patterns of replication in the various stages of S-phase in Amphibia. Several possibilities for the use of this technique were demonstrated on three frog species of the family Ranidae, all differing greatly in their DNA-content. With this method, the homomorphic chromosome pair No. 4 in Rana esculenta could be identified as sex-specific chromosomes of the XX/XY-type. All male animals exhibit an extremely late replicating region in the Y-chromosome, which is lacking in the X-chromosome in the female animals, both X-chromosomes replicate synchronously. These sex-specific chromosomes cannot be distinguished by other banding techniques. In the highly heteromorphic ZZ/ZW-sex chromosome system of Pyxicephalus adspersus a synchronous replication of the two Z-chromosomes of male animals and a very late replication of the short arm of the W-chromosomes of male animals was demonstrated. These results support the assumption that there is no dosage compensation for Z-linked or X-linked genes by the sex chromosome inactivation mechanism in the sex chromosomes of Amphibia.
TL;DR: A female with Duchenne muscular dystrophy who was a carrier of a balanced translocation t(X;6)(p21;q21) is reported, and the extremely low probability of five independent (X;A) translocations having a breakpoint at Xp21 points to a non-rand association of this site with the DMD phenotype.
Abstract: A female with Duchenne muscular dystrophy who was a carrier of a balanced translocation t(X;6)(p21;q21) is reported. Four other previously described (X;A) translocations associated with DMD share with the present case a breakpoint at Xp21. The extremely low probability of five independent (X;A) translocations having a breakpoint at Xp21 points to a non-rand association of this site with the DMD phenotype. A DMD locus at Xp21 could be damaged by the translocation, giving rise to Duchenne muscular dystrophy. Alternatively, a pre-existing DMD gene could weaken the chromosome, favouring breaks at Xp21.
TL;DR: A functional CAD gene from Syrian hamster cells is cloned using a cosmid vector and introduced into CAD-deficient Chinese hamster ovary (CHO) cell mutants by fusing them with protoplasts of Escherichia coli containing the cosmids.
TL;DR: Six regions on the Y chromosome of Drosophila melanogaster necessary for male fertility are defined and localize and appear to contain but one functional unit, as defined by failure of complementation among translocations with breakpoints within the same block.
Abstract: Cytological and genetic analyses of 121 translocations between the Y chromosome and the centric heterochromatin of the X chromosome have been used to define and localize six regions on the Y chromosome of Drosophila melanogaster necessary for male fertility. These regions are associated with nonfluorescent blocks of the Y chromosome, as revealed using Hoechst 33258 or quinacrine staining. Each region appears to contain but one functional unit, as defined by failure of complementation among translocations with breakpoints within the same block. The distribution of translocation breakpoints examined appears to be nonrandom, in that breaks occur preferentially in the nonfluorescent blocks and not in the large fluorescent blocks.
TL;DR: It is demonstrated that oogonia have a single active X chromosome and that the inactive X chromosome is reactivated at or, more likely, shortly before entry into meiotic prophase.
Abstract: Mature mammalian oocytes have both of their X chromosomes active, while somatic cells from the same individual have one of their X chromosomes in an inactive state. We asked whether the X chromosomes of the germ cells never undergo inactivation in their ontogeny or whether inactivation of an X chromosome does occur but is followed by a subsequent reactivation event. Our approach has used an electrophoretic polymorphism for the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) in the mouse species Mus caroli. G6PD is dimeric, and a heterodimer is produced in cells from heterozygous females if and only if both X chromosomes are active. Ovaries from heterozygous fetuses at different gestational ages were dissected and either studied cytologically or pressed between microscopy slides to obtain germ cell-rich and germ cell-poor preparations. No heterodimer band was detected on the 10th day of development in germ cell-rich preparations. On subsequent days, an increasingly intense heterodimer band was detected, which, by the 13th day, was approximately twice as intense as the corresponding homodimer bands. Consideration of (i) the G6PD activity per germ cell and per somatic cell and (ii) the percentage of germ cells in the germ cell-rich preparations indicated that a heterodimer band should have been visible on the 10th day had both X chromosomes been active. Cytological examinations showed that the earliest germ cells enter meiotic prophase on the eleventh day. These results demonstrate that oogonia have a single active X chromosome and that the inactive X chromosome is reactivated at or, more likely, shortly before entry into meiotic prophase.
TL;DR: It seems reasonable to conclude that the recovered X-ray-induced mutants available for analysis do not represent a random sample of those initially induced in the exposed male germ cells.
Abstract: Cytogenetic analysis of more than 1500 randomly recovered lethal X chromosomes derived from 2000 and 3000 r X-ray exposures of post-meiotic male germ cells has made possible a plot of the distribution in different regions of the X chromosome of: (1) gene mutations associated with cytologically normal chromosomes, (2) mutations associated with chromosomal rearrangement breakpoints, (3) deficiencies, and (4) rearrangement breakpoints whether or not they are associated with mutations. The distribution of point mutations, vital loci and rearrangement breakpoints in different regions of the X chromosome is not proportional to either the number of bands or the relative DNA content. Further, the density of vital loci (those capable of mutating to a lethal allele) is quite different in some regions as compared to others. For example, vital loci in the 3AB region, which has been thoroughly studied by Judd and others, are at least as numerous as bands; whereas, the 3CD region, equally long, has only two vital loci. Other regions densely populated with vital loci include 1B, 1F-2A, 10A, 11A, and 19EF; sparsely populated regions include 6EF and 10B-10E. It seems reasonable to conclude that the recovered X-ray-induced mutants available for analysis do not represent a random sample of those initially induced in the exposed male germ cells.
TL;DR: It is suggested that the X chromosome possesses only one inactivation center, and results of this study allowed a more precise localization of this inactivation centre.
Abstract: The observation of five special cases of structural anomalies involving the X chromosomes led us to study the inactivation center. These data, combined with those from the literature, suggest that the X chromosome possesses only one inactivation center. Results of this study allowed a more precise localization of this inactivation center.
TL;DR: The main determinant of gonadal differentiation appears to be the presence or absence of a cell surface antigen, called H-Y antigen, which involves the interaction between regulatory sites on the Y chromosome, the X chromosome, and possibly the autosomes.
Abstract: 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
TL;DR: Several lines of evidence presented here show that the chromosomal positions of at least some P factors can be identified as points of frequent chromosome breakage (hotspots) and a new procedure for efficiently determining the positions of hotspots on a given chromosome is described.
TL;DR: No germ cells in meiosis were found in the fetal testes of XY males, nor of XO Sex-reversed males, so it is suggested that a second X chromosome renders a germ cell more susceptible to the meiosis-inducing influence of the mesonephric rete.
Abstract: XX germ cells in the fetal testes of XX Sex-reverse male mice were observed mostly to develop in the same manner as do XY germ cells in a normal fetal testis; but some, in the vicinity of the mesonephric rete region, entered the prophase of meiosis at the same time as do XX germ cells in a normal fetal ovary. No germ cells in meiosis were found in the fetal testes of XY males, nor of XO Sex-reversed males. It is suggested that a second X chromosome renders a germ cell more susceptible to the meiosis-inducing influence of the mesonephric rete.
TL;DR: It was found that male mating behavior is controlled by factors located in the PGM-marked chromosome and in the Y chromosome, and there appears to be no correlation between a chromosome's structural diversity and its contribution to sexual isolation.
Abstract: The chromosomal determination of interspecific differences in mating behavior was studied in the interfertile pair, Drosophila arizonensis and Drosophila mojavensis, by means of chromosomal substitutions. Interspecific crossing over was avoided by crossing hybrid males to parental females, and identification of the origin of each chromosome in backcrossed hybrids was possible by means of allozyme markers. It was found that male mating behavior is controlled by factors located in the PGM-marked chromosome (which, in other Drosophila species, is part of the X chromosome) and in the Y chromosome. The other chromosomes influence male sexual behavior through their interactions with each other and with the PGM-marked chromosome, but their overall effect is minor. Female mating behavior is controlled by factors located in the ODH-marked and AMY-marked chromosomes, with the other chromosomes exercising a small additive effect. Hence, the two sex-specific behaviors are under different genetic control. Cytoplasmic origin has no effect on the mating behavior of either sex. There appears to be no correlation between a chromosome's structural diversity (i.e., amounts of inversion polymorphism within a species or numbers of fixed inversions across species) and its contribution to sexual isolation. These findings are in general agreement with those from similar Drosophila studies and may not be specific to the species studied here.
TL;DR: Evidence indicates that the structural gene for the flavin polypeptide of MAO-A is on the human X chromosome, which represents the first chromosomal assignment of a human gene coding for an enzyme of neurotransmitter metabolism.
Abstract: Inherited variations in monoamine oxidase (MAO) activity are thought to affect human behavior and expression of disease. The present study has established the chromosomal location of one of the structural genes coding for this enzyme. Mapping was carried out by somatic cell hybridization between normal human skin fibroblasts and mouse neuroblastoma cells. Selective media for growth of cells with or without hypoxanthine phosphoribosyltransferase (HPRT) activity were used to obtain hybrid lines which had retained or lost the human X chromosome, respectively. Cytogenetic techniques, isozyme analysis, and limited proteolysis and peptide mapping of [3H]pargyline-labeled MAO were used to characterize hybrid lines. With one exception, only lines containing the human X chromosome and human forms of two X-linked enzymes (phosphoglycerate kinase and glucose-6-phosphate dehydrogenase) expressed the human form of the flavin polypeptide of type A MAO. The exceptional hybrid line contained a putative translocation of part of the human X chromosome, since it expressed human forms of both MAO and phosphoglycerate kinase but neither the human form of glucose-6- phosphate dehydrogenase nor HPRT activity. This evidence indicates that the structural gene for the flavin polypeptide of MAO-A is on the human X chromosome. This represents the first chromosomal assignment of a human gene coding for an enzyme of neurotransmitter metabolism. This information will help to elucidate the structure of MAO and modes of its inheritance in the human population.
TL;DR: The genetic determination of resistance to the sterility-producing genetic elements called P factors was studied in a strain characterized as neutral (Q) in the P-M system of hybrid dysgenesis, and cytotype was found to be primarily controlled by the genotype, but the maternal cytoplasm, under some circumstances, has an important short-term effect.
Abstract: The genetic determination of resistance to the sterility-producing genetic elements called P factors was studied in a strain characterized as neutral ( Q ) in the P-M system of hybrid dysgenesis. Sixteen lines were synthesized, representing all possible homozygous combinations of the three major chromosomes and differing maternal cytoplasms of an original resistant ( Q ) and susceptible ( M ) strain.—The results provide a detailed genetic analysis of the determination of cytotype (which mediates resistance or susceptibility to P factors) in the absence of the P-M dysgenic interaction. They extend the findings of Engels (1979) by providing specific information on both the location and relative magnitude of effect of cytotype-determining chromosomal factors and their interaction over time with maternally transmitted cytoplasm.—Cytotype was found to be primarily controlled by the genotype, but the maternal cytoplasm, under some circumstances, has an important short-term effect. Major cytotype-determining chromosomal factors are localized to the distal half of the X chromosome. However, there was also evidence for minor factors located on the major autosomes, particularly chromosome 3. Under certain circumstances, cytotypic switches in either direction can be produced in a single generation by the substitution of an X chromosome carrying a major cytotype determinant. This may provide an explanation of why reciprocal differences have sometimes been interpreted as direct effects of X -chromosome suppressors. However, slow but systematic changes of M to P cytotype were observed in five synthesized lines of mixed origin over twenty generations with no chromosomal substitution. Alternative explanations of these changes in terms of delayed effects of minor autosomal factors or of the transposability of cytotype determinants are discussed.
TL;DR: The functional role of H-Y antigen in directing differentiation of the heterogametic gonad appears to have been preserved during evolution, but the mechanism of its control has changed and this latter mechanism is only poorly understood.
Abstract: While it remains to be clarified what detection of H-Y antigen by current methods means, the existence of a factor governing testicular differentiation of the indifferent gonadal anlage seems to be well established. There are various kinds of evidence that H-Y antigen as a biologically meaningful factor has a complex genetical basis. There is the contribution of the Y chromosome which, independent of the number of other chromosomes, especially of X chromosomes, leads to a male phenotype. The X chromosome must be involved also because structural aberrations of its distal short arm influence the expression of the H-Y structural gene. Due to examples of autosomal inheritance of various forms of sex reversal, an autosomal gene is assumed to be involved as well. Arguments are presented favoring the assumption that the structural H-Y gene is autosomal, while genes on the X and Y chromosomes have a controlling function. This genetic control mechanism for H-Y antigen seems to have evolved secondary to placentation in mammals. In non-mammalian vertebrates, H-Y antigen is controlled by other factors, e.g. steroid hormones. While the functional role of H-Y antigen in directing differentiation of the heterogametic gonad appears to have been preserved during evolution, the mechanism of its control has changed. This latter mechanism is only poorly understood.
Journal Article•
TL;DR: The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from 12 1/2-day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1), confirming Johnston's evidence that Pgk-1 expression reflects a single active X chromosome at this time.
Abstract: The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from 12 1/2-day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle's translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chromosome is expressed. This confirms Johnston's evidence (1979, 1981) that Pgk-1 expression reflects a single active X chromosome at this time. Extracts of 12 1/2-day germ cells from heterozygous females carrying two normal X chromosomes show both the A and the B forms of PGK; since only one X chromosome in each cell is active, different alleles must be expressed in different cells, suggesting that X-chromosome inactivation is normally random in the germ line. This result makes it unlikely that germ cells are derived from the yolk-sac endoderm where the paternally derived X chromosome is preferentially inactivated. In their pattern of X-chromosome inactivation, germ cells evidently resemble other tissues derived from the epiblast.
TL;DR: The ratio of enzyme activities in XX Sxr/+ prosper matogonia was significantly higher than that in XY prospermatogonia, suggesting that the silent X chromosome is reactivated in XX male germ cells before birth, as it is in female germ cells.
Abstract: Summary. Germ cells were isolated from XX ovaries and XY and XX sex-reversed (Sxr/+) testes of mouse embryos 14\p=n-\16days post coitum, and the activity of an X-chromosome-coded enzyme, hypoxanthine phosphoribosyl transferase (HPRT), relative to an autosomal one, adenine phosphoribosyl transferase was determined. The ratio of enzyme activities in XX Sxr/+ prospermatogonia was significantly higher than that in XY prospermatogonia, up to 2-fold, suggesting that the silent X chromosome is reactivated in XX male germ cells before birth, as it is in female germ cells. The ratio was several times higher still in XX oocytes than in XX prospermatogonia, confirming that the increase in HPRT activity reported in oocytes is only partly due to an X-chromosome dosage effect.
TL;DR: Linkage tests with Mo vbr and Ta demonstrate that the mouse X chromosomal locus, Xce, lies close to Ta, and provide genetic evidence which establish that the C3H/HeH X chromosome carries the Xce a allele of this gene and the JU/FaCt and C57BL/GoH X chromosomes carry theXce b allele.
Abstract: Previous studies have shown that the mouse X chromosomal locus, Xce, which causes non-random X chromosome inactivation, is closely linked to the Is(X; 7)Ct X-autosome translocation. This has placed it either near Ta on one side of the breakpoint or near jp on the other. Linkage tests with Movbr and Ta now demonstrate that the locus in fact lies close to Ta. The data also provide genetic evidence which establish that the C3H/HeH X chromosome carries the Xcea allele of this gene and the JU/FaCt and C57BL/GoH X chromosomes carry the Xceb allele, and further suggest that the X-linked modification of the heterozygous phenotypes of X-linked genes observed by various other investigators are all attributable to differences at the Xce locus. Evidence of a maternal influence upon Movbr phenotypes is also presented. This appears to operate independently of the X-inactivation process, probably through an effect of differing levels of copper in the milk in early life upon the mutant coat colour in the young.
TL;DR: The major type I insert sequence for the 28S rRNA genes of Drosophila melanogaster has been mapped within the chromosomes using a probe synthesized from a cloned sequence containing the entire 5·4 kb segment.
Abstract: The major type I insert sequence for the 28S rRNA genes of Drosophila melanogaster has been mapped within the chromosomes using a probe synthesized from a cloned sequence containing the entire 5·4 kb segment. The genomic distribution was shown to be complex in that the insert sequence occurred next to many different types of sequences, in addition to occurring as an insert in the 28S rRNA genes of the X chromosome. In situ hybridization of mitotic chromosomes showed most of the insert units not contained in the ribosomal genes to be located near the ribosomal gene cluster on the X chromosome. Additional sites were detected in polytene chromosomes in region 102C, 8–12 and in the hetero-chromatin of the autosomes.