Biomedical subjects

D C Page

Publications and source records attributed to D C Page.

At least 19 recordsLinked to original sources

PubMed1992

The human Y chromosome: overlapping DNA clones spanning the euchromatic region.

The human Y chromosome was physically mapped by assembling 196 recombinant DNA clones, each containing a segment of the chromosome, into a single overlapping array. This array included more than 98 percent of the euchromatic portion of the Y chromosome. First, a library of yeast artificial chromosome (YAC) clones was prepared from the genomic DNA of a human XYYYY male. The library was screened to identify clones containing 160 sequence-tagged sites and the map was then constructed from this information. In all, 207 Y-chromosomal DNA loci were assigned to 127 ordered intervals on the basis of their presence or absence in the YAC's, yielding ordered landmarks at an average spacing of 220 kilobases across the euchromatic region. The map reveals that Y-chromosomal genes are scattered among a patchwork of X-homologous, Y-specific repetitive, and single-copy DNA sequences. This map of overlapping clones and ordered, densely spaced markers should accelerate studies of the chromosome.

Base Sequence↗

PubMed1992

The human Y chromosome: a 43-interval map based on naturally occurring deletions.

A deletion map of the human Y chromosome was constructed by testing 96 individuals with partial Y chromosomes for the presence or absence of many DNA loci. The individuals studied included XX males, XY females, and persons in whom chromosome banding had revealed translocated, deleted, isodicentric, or ring Y chromosomes. Most of the 132 Y chromosomal loci mapped were sequence-tagged sites, detected by means of the polymerase chain reaction. These studies resolved the euchromatic region (short arm, centromere, and proximal long arm) of the Y chromosome into 43 ordered intervals, all defined by naturally occurring chromosomal breakpoints and averaging less than 800 kilobases in length. This deletion map should be useful in identifying Y chromosomal genes, in exploring the origin of chromosomal disorders, and in tracing the evolution of the Y chromosome.

Base Sequence↗

PubMed1992

Cytogenetic and molecular characterization of marker chromosomes in patients with mosaic 45,X karyotypes.

Cytogenetic and molecular techniques were employed to determine the origin of marker chromosomes in five patients with mosaic 45,X karyotypes. The markers were shown to be derived from the X chromosome in three female patients and from the Y chromosome in one female and one male. One of the female patients, with a very small, X-derived ring chromosome, had additional phenotypic abnormalities not typically associated with Turner syndrome. In this patient, both the ring and the normal X chromosomes replicated early; perhaps the unusual phenotype is the result of both chromosomes remaining transcriptionally active. These studies illustrate the power of resolution and utility of combined cytogenetic and molecular approaches to some clinical cases.

Adolescent↗

PubMed1992

Rps4 maps near the inactivation center on the mouse X chromosome.

RPS4Y, a Y-linked gene in humans, appears to encode an isoform of ribosomal protein S4. A homologous locus on the human X chromosome, RPS4X, lies close to the X-inactivation center but fails to undergo X-inactivation. We have isolated a genomic clone from the mouse Rps4 locus, the homolog of human RPS4X. We derived an intron probe that hybridizes to the functional Rps4 locus but does not cross-hybridize to related sequences elsewhere in the mouse genome. Genetic mapping utilizing interspecific mouse backcrosses and the intron-specific probe demonstrates that Rps4 maps close to the Phka locus on the mouse X chromosome and in the vicinity of the X-inactivation center. The gene order Ccg-1-Rps4/Phka-Xist-Pgk-1 is conserved between mouse and human.

Animals↗

PubMed1991

Inactivation of the Zfx gene on the mouse X chromosome.

ZFX, an X chromosome-linked gene encoding a zinc-finger protein, has previously been shown to escape X inactivation in humans. Here we report studies of the inactivation status of the homolog, Zfx, on the mouse X chromosome. We took advantage of both the preferential inactivation of the normal X chromosome in females carrying the T(X;16)16H translocation and the high degree of nucleotide sequence variation between the laboratory strain of mouse [corrected] and Mus spretus genomes. An EcoRV restriction fragment difference between laboratory strain of mouse [corrected] and M. spretus was detected after amplification of Zfx transcripts using the reverse transcription-polymerase chain reaction. Using this allelic variation, we assessed expression of the two Zfx genes in females carrying the T(X;16)16H translocation (from laboratory strain of mouse [corrected]) and an intact X chromosome (from M. spretus). Such females exhibit Zfx transcription from the active laboratory strain of mouse [corrected] chromosome but not from the inactive M. spretus chromosome. These results indicate that the mouse Zfx gene is subject to X inactivation.

Animals↗

PubMed1991

Inactivation of the Rps4 gene on the mouse X chromosome.

The human RPS4X and RPS4Y genes, located on the X and Y chromosomes, appear to encode isoforms of ribosomal protein S4. Haploinsufficiency of these genes may contribute to the human phenotype known as Turner syndrome. Although RPS4X maps near the X-inactivation center, the gene is expressed on inactive human X chromosomes. We cloned Rps4, the mouse homolog of RPS4X. Exploiting allelic variation in Rps4, we examined transcription of the gene from active and inactive mouse X chromosomes in vivo, in female mice carrying an X-autosome translocation. We report that mouse Rps4, unlike human RPS4X, is subject to X inactivation. This finding may explain, at least in part, why the phenotypic consequences of X monosomy are less severe in mice than in humans.

Alleles↗

PubMed1991

An interstitial deletion in mouse Y chromosomal DNA created a transcribed Zfy fusion gene.

The small portion of the mouse Y chromosome retained in the Sxra transposition is thought to carry at least five genes including, as demonstrated here, the entirety of the zinc-finger genes Zfy-1 and Zfy-2. Sxrb, a derivative of Sxra, was previously thought to retain Zfy-1 but to be deleted for Zfy-2. Here we show that Sxrb differs from Sxra as the result of unequal crossing-over between Zfy-1 and Zfy-2. This unequal crossing-over created a transcribed Zfy-2/1 fusion gene and an interstitial deletion. Our data and previous results together suggest that this deletion encompassed the 3' portion of Zfy-2, the histocompatibility gene Hya, the spermatogenesis factor Spy, and the 5' portion of Zfy-1. We suggest that not only Zfy but also other neighboring genes such as Spy and Hya may exist in two copies on the Y as the result of a large tandem duplication during rodent evolution.

Animals↗

PubMed1991

XY chromosome nondisjunction in man is associated with diminished recombination in the pseudoautosomal region.

To assess the possible association between aberrant recombination and XY chromosome nondisjunction, we compared pseudoautosomal region recombination rates in male meiosis resulting in 47,XXY offspring with those resulting in 46,XY and 46,XX offspring. Forty-one paternally derived 47,XXYs and their parents were tested at six polymorphic loci spanning the pseudoautosomal region. We were able to detect crossing-over in only six of 39 cases informative for the telomeric DXYS14/DXYS20 locus. Subsequently, we used the data to generate a genetic linkage map of the pseudoautosomal region and found it to be significantly shorter than the normal male map of the region. From these analyses we conclude that most paternally derived 47,XXYs result from meiosis in which the X and Y chromosomes did not recombine.

Chromosome Mapping↗

PubMed1990

Homologous ribosomal protein genes on the human X and Y chromosomes: escape from X inactivation and possible implications for Turner syndrome.

We have isolated two genes on the human sex chromosomes, one on the Y and one on the X, that appear to encode isoforms of ribosomal protein S4. These predicted RPS4Y and RPS4X proteins differ at 19 of 263 amino acids. Both genes are widely transcribed in human tissues, suggesting that the ribosomes of human males and females are structurally distinct. Transcription analysis revealed that, unlike most genes on the X chromosome, RPS4X is not dosage compensated. RPS4X maps to the long arm of the X chromosome (Xq), where no other genes are known to escape X inactivation. Curiously, RPS4X maps near the site from which the X-inactivating signal is thought to emanate. On the Y chromosome, RPS4Y maps to a 90 kb segment that has been implicated in Turner syndrome. We consider the possible role of RPS4 haploinsufficiency in the etiology of the Turner phenotype.

Amino Acid Sequence↗

PubMed1990

Additional deletion in sex-determining region of human Y chromosome resolves paradox of X,t(Y;22) female.

Whether a human embryo develops as a male or a female is determined by the presence of the Y chromosome. The sex-determining function lies entirely in interval 1A, inasmuch as most XX individuals with descended testes and normal male external genitalia carry this small region of the Y chromosome. We have localized an essential part of the sex-determining function to a portion of interval 1A, on the basis of the discovery of a female with a reciprocal Y;22 translocation and part of 1A deleted at the translocation breakpoint. Recently, a paradox has arisen with the report of four partially masculinized XX individuals who carry only a portion of interval 1A--a portion that does not overlap the deletion in the X,t(Y;22) female. These recent findings imply that the sex-determining function lies in the portion of 1A present in the four XX intersexes and not in the portion deleted in the X,t(Y;22) female. To explain the X,t(Y;22) individual, it was proposed that she was female because of a chromosomal position effect or delayed development of the gonadal soma. Here we report that the X,t(Y;22) female has a deletion of a second portion of interval 1A--a portion corresponding closely to that present in the XX intersexes. This resolves the apparent contradiction. Nonetheless, phenotype-genotype correlations suggest that two or more genetic elements in interval 1A may contribute to the sex-determining function of the Y chromosome. The X,t(Y;22) female lacks the ZFY gene but does not exhibit the complex phenotype known as Turner's syndrome, arguing against the hypothesis that ZFY is the Turner's syndrome gene on the Y chromosome.

Chromosome Deletion↗

PubMed1990

Human sex-chromosome-specific repeats within a region of pseudoautosomal/Yq homology.

Several categories of human X-Y homologous DNA sequences have been recognized. We report that a locus (DXYS77) approximately 14 kb distal to the pseudoautosomal boundary (PAB) is 93% identical in nucleotide sequence to a locus (DYS148) on the long arm of the Y chromosome (Yq). Within this segment of pseudoautosomal/Yq homology we identified a member of a family of repeats that are concentrated in Xp22.3 and in the euchromatic portion of the Y chromosome. The repeat sequence structure--a dimer bounded by short terminal repeats--is reminiscent of retroposons derived from RNA polymerase III transcripts.

Base Sequence↗

PubMed1990

Chromosomal localization of ZFX--a human gene that escapes X inactivation--and its murine homologs.

The ZFY gene, found in the sex-determining region of the human Y chromosome, encodes a zinc-finger protein that may be the pivotal sex-determining signal. A closely related gene, ZFX, is found on the human X chromosome, and it may also function in sex determination. ZFX is one of a few genes on the human X chromosome that are known to escape X inactivation. We report the localization of ZFX, by meiotic linkage analysis and physical mapping, distal to POLA but proximal to DXS41 (p99-6), near the boundary of bands Xp21.3 and Xp22.1. (Our results suggest the following order of loci in Xp21-p22: cen-DMD-[GK,AHC]-DXS67 (pB24)-POLA-ZFX-[DXS41 (p99-6), DXS274 (CRI-L1391)]-DXS43 (pD2)-pter.) These findings contradict the model that escape from X inactivation is limited to genes near the short-arm telomere (i.e., in Xp22.3). Instead, escape from X inactivation is likely a property of several noncontiguous segments of the X chromosome. Curiously, in mouse, the homologous Zfx gene maps to X chromosome band D, near the center from which an X-inactivating signal is thought to spread. As judged by comparative mapping, it appears that an X-chromosomal segment that spans the ZFX and DMD genes has remained grossly intact during the divergence of mouse and human from a common ancestor. Conservation of this chromosomal segment may extent to marsupials, where homologs of the ZFX and DMD genes have been observed in proximity, but on an autosome. While autosomal homologs of ZFX have not been observed in other placental mammals, a locus derived from a processed Zfx transcript is found on mouse chromosome 10 band B3 or B4.

Animals↗

PubMed1990

Mouse Zfx protein is similar to Zfy-2: each contains an acidic activating domain and 13 zinc fingers.

The Zfy gene is located on the Y chromosome of placental mammals and encodes a zinc finger protein which may serve as the primary sex-determining signal. A related gene, Zfx, is similarly conserved on the X chromosome. Unlike that in most mammals, the mouse genome contains four homologous zinc finger loci: Zfy-1, Zfy-2, Zfx, and Zfa (on an autosome). We report that, in contrast to the mouse Zfy genes, Zfx is widely transcribed in embryos, newborns, and adults, both male and female. Moreover, Zfx transcripts contain long 3' untranslated sequences which are phylogenetically conserved. Zfa is a processed gene derived from Zfx. An analysis of cDNA clones demonstrated that Zfx encodes a 799-amino-acid protein that is 70% identical to the mouse Zfy-1 and Zfy-2 proteins. Zfx, Zfy-1, and Zfy-2 contain highly acidic amino-terminal domains and carboxy-terminal regions containing 13 zinc fingers. When fused to the DNA-binding domain of GAL4, the acidic domains of Zfx and Zfy-2 activated transcription in yeast cells.

Amino Acid Sequence↗

PubMed1990

A bird zinc-finger protein closely related to ZFY.

The ZFY gene is thought to reside in the "sex-determining" region of the mammalian Y chromosome and encodes a zinc-finger protein that may function in determining the sex of embryos. Although birds have a ZZ(male)/ZW(female) sex-determination system, they possess a gene, Zfb, that is highly homologous to ZFY. We used ZFY as a hybridization probe to clone the zinc-finger domain of the chicken Zfb gene. Chicken Zfb is widely transcribed in male and female tissues and encodes a protein with a zinc-finger domain that is 93% identical in amino acid sequence to the zinc-finger domain of ZFY. Thus, the putative DNA-binding domains of the Zfb and ZFY proteins diverged little from a common ancestral protein that existed prior to birds and mammals, suggesting that the DNA binding site has been similarly conserved. The absence of sex differences in the hybridization patterns of Zfb raises the question of whether this gene is present on the Z/W sex chromosomes in birds.

Age Factors↗

PubMed1990

Steroid sulfatase gene in XX males.

The human X and Y chromosomes pair and recombine at their distal short arms during male meiosis. Recent studies indicate that the majority of XX males arise as a result of an aberrant exchange between X and Y chromosomes such that the testis-determining factor gene (TDF) is transferred from a Y chromatid to an X chromatid. It has been shown that X-specific loci such as that coding for the red cell surface antigen, Xg, are sometimes lost from the X chromosome in this aberrant exchange. The steroid sulfatase functional gene (STS) maps to the distal short arm of the X chromosome proximal to XG. We have asked whether STS is affected in the aberrant X-Y interchange leading to XX males. DNA extracted from fibroblasts of seven XX males known to contain Y-specific sequences in their genomic DNA was tested for dosage of the STS gene by using a specific genomic probe. Densitometry of the autoradiograms showed that these XX males have two copies of the STS gene, suggesting that the breakpoint on the X chromosome in the aberrant X-Y interchange is distal to STS. To obtain more definitive evidence, cell hybrids were derived from the fusion of mouse cells, deficient in hypoxanthine phosphoribosyltransferase, and fibroblasts of the seven XX males. The X chromosomes in these patients could be distinguished from each other when one of three X-linked restriction-fragment-length polymorphisms was used. Hybrid clones retaining a human X chromosome containing Y-specific sequences in the absence of the normal X chromosome could be identified in six of the seven cases of XX males.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Putative transcription activator with alternative isoforms encoded by human ZFX gene.

The ZFY gene in the sex-determining region of the human Y chromosome encodes a protein with 13 zinc fingers, and may determine whether an embryo develops as a male or female. ZFX, a related gene on the human X chromosome, may also function in sex determination; it encodes a protein with a very similar zinc-finger domain and escapes X inactivation. ZFY and ZFX diverged from a common ancestral gene before the radiation of placental mammals, and retain a similar genomic organization. Analysis of complementary DNAs from the mouse Y-chromosomal homologues of ZFY indicates that these genes encode probable transcription activators. Here, we report that ZFX encodes a protein composed of a highly acidic amino-terminal domain, a basic putative nuclear-localization signal, and a carboxy-terminal zinc-finger domain. This combination of features, also found in the ZFY gene product, is typical of transcription activators. Alternative splicing generates ZFX transcripts encoding isoforms of 575 and 804 amino acids. These ZFX protein isoforms differ in the length of their acidic domains and may be functionally distinct.

Amino Acid Sequence↗

PubMed1989

ZFX has a gene structure similar to ZFY, the putative human sex determinant, and escapes X inactivation.

The ZFX gene on the human X chromosome is structurally similar to the ZFY gene, which may constitute the sex-determining signal on the human Y chromosome. ZFY and ZFX diverged from a common ancestral gene, as evidenced by similarities in their intron/exon organization and exon DNA sequences. The carboxy-terminal exons of ZFY and ZFX both encode 13 zinc fingers; 383 of 393 amino acid residues are identical, and there are no insertions or deletions. Thus, the ZFY and ZFX proteins may bind to the same nucleic acid sequences. ZFY and ZFX are transcribed in a wide variety of XY and (in the case of ZFX) XX cell lines. Transcription analysis of human-rodent hybrid cell lines containing "inactive" human X chromosomes suggests that ZFX escapes X inactivation. This result contradicts the "dosage/X-inactivation" model, which postulated that sex is determined by the total amount of functionally interchangeable ZFY and ZFX proteins.

Base Sequence↗

PubMed1989

The sex-determining region of the mouse Y chromosome encodes a protein with a highly acidic domain and 13 zinc fingers.

The ZFY gene, located in the sex-determining region of the human Y chromosome, appears to encode a zinc-finger protein. Two homologous genes, Zfy-1 and Zfy-2, are found in the sex-determining region of the mouse Y chromosome. One or both genes may serve as the primary sex-determining signal in mice. Both Zfy-1 and Zfy-2 are transcribed in the adult testis. Nucleotide sequence analysis of a Zfy-2 cDNA suggests that it encodes a 783 amino acid protein with two domains: the amino-terminal portion is highly acidic, with 25% of its residues being glutamic or aspartic acid, while the carboxy-terminal domain contains 13 zinc fingers. The presence in Zfy-2 of an acidic domain in combination with a putative nucleic acid binding domain suggests that Zfy-2 activates transcription in a sequence-specific fashion.

Animals↗