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C J Brown

Publications and source records attributed to C J Brown.

At least 109 records · Page 6Linked to original sources
PubMed1993

Mapping of the distal boundary of the X-inactivation center in a rearranged X chromosome from a female expressing XIST.

A female patient with primary amenorrhea, immature secondary sexual characteristics, and tall stature was found to have a normal X chromosome and a rearranged X [rea(X)] chromosome that resembled an 'isochromosome' Xp, but retained the proximal portion of Xq. The rea(X) was interpreted as rec(X)dup p,inv(X)(p11.4q13). Replication studies demonstrated that the rea(X) was always the late-replicating and, therefore, presumably inactive X chromosome, which must contain the X-inactivation center. Consistent with this interpretation, fluorescence in situ hybridization demonstrated that the rea(X) retained the XIST gene, and reverse transcription polymerase chain reaction analysis showed that XIST was expressed in the patient's cells. By fluorescence in situ hybridization with previously mapped probes, the breakpoint of the rea(X) was located within an approximately 500-kb region located approximately 200 to 700 kb distal to the XIST locus. This is the closest breakpoint distal to XIST in an inactivated X chromosome and, therefore, defines a new distal boundary for the X-inactivation center in humans.

Adolescent↗
PubMed1993

The interleukin-2 receptor gamma chain maps to Xq13.1 and is mutated in X-linked severe combined immunodeficiency, SCIDX1.

The gene encoding the gamma chain of the lymphocyte interleukin-2 receptor has been cloned and shown to be required to associate with the beta chain in order for IL-2 internalization and cell activation to occur (1). We considered this gene, IL2RG, a candidate for the X-linked form of severe combined immunodeficiency at the SCIDX1 locus, in which affected males have impaired lymphocyte development. Using fluorescence in situ hybridization and PCR amplification of somatic cell hybrid DNAs, we mapped IL2RG to human Xq13.1, a location within the SCIDX1 critical region established by linkage analysis. The 4.2 kb IL2RG gene was sequenced, and its genomic organization was elucidated. Seven of 19 transformed B-lymphocyte cell lines with independent SCIDX1 mutations had absent or minimal IL2RG mRNA. Unique point mutations were documented to be specifically associated with the disease and the carrier state in four unrelated affected males and their family members: one in a boy with no detectable IL2RG mRNA, in which the mutation ablated a splice donor site; one causing premature chain termination; and two causing distinct amino acid changes. The demonstration of impaired IL2RG mRNA expression in males with X-linked SCID and of unique point mutations in SCIDX1 pedigrees constitutes powerful evidence that the SCIDX1 gene is IL2RG. Noguchi et al. (2) have independently published IL2RG mapping to Xq13 and discovery of mutations in three affected males. The specific pathogenesis of IL2RG mutations and approaches to gene therapy can now be addressed in the X-linked form of SCID.

Amino Acid Sequence↗
PubMed1993

2.6 Mb YAC contig of the human X inactivation center region in Xq13: physical linkage of the RPS4X, PHKA1, XIST and DXS128E genes.

X chromosome inactivation is a mechanism of dosage compensation that regulates the expression of mammalian X-linked genes between XY males and XX females. This phenomenon is cis-acting, clonally heritable, and requires the presence of an X inactivation center (XIC). In our attempts to characterize this phenomenon, we have focused on the physical organization of the human XIC localized to Xq13. From previous studies, we had determined that the candidate XIC interval contained two loci (DXS128 and XIST) and was bound by the breakpoints of two structurally abnormal inactivated X chromosomes, a t(X;14) and an idic(Xp). Here we present a refined mapping of the XIC-containing region using the breakpoint of a late replicating rearranged X (rea(X)), and the initial characterization of a set of 40 yeast artificial chromosomes (YACs) derived from the XIC-containing region. These YACs form a 2.6 Mb contig which completely covers the XIC, and physically links the RPS4X, PHKA1, XIST, and DXS128E genes, as well as a laminin receptor pseudogene (LAMRP4). Furthermore, we have determined the relative orientations of these four genes, and have derived a restriction map of the region using the rare cutter enzymes BssHII, EagI, MluI, NruI, SalI, SfiI, SstII (or SacII), and NotI. We have identified at least 9 CpG-rich islands within this region, and have discovered a large (approximately 125 kb) inverted duplication proximal to the XIC based on symmetrical restriction patterns and homologous probes. We estimate the maximum size of the XIC-containing interval to be between 680 kb and 1200 kb, based on the localization of the breakpoints of the rearranged X chromosomes mentioned above. This lays the groundwork for the further characterization of the XIC region and the isolation of other expressed sequences therefrom.

Amino Acid Sequence↗
PubMed1992

Expression of the human ADH2 gene: an unusual Sp1-binding site in the promoter of a gene expressed at high levels in liver.

The sequence 5'-GTGGGTGTGGC (G3T) is important for the efficient initiation of transcription from the human ADH2 promoter. We show here that the purified transcription factor Sp1 binds with high affinity to the G3T site of ADH2 (encoding beta beta-alcohol dehydrogenase), even though the G3T sequence does not contain the canonical Sp1-binding site, GGGCGG. Proteins from mouse liver nuclei and purified Sp1 both footprint the same sequence of the ADH2 promoter with similar patterns. UV crosslinking demonstrates that the major G3T-binding protein in the liver extract is similar in size to Sp1. Mouse liver nuclear extract resembles purified Sp1 in its relative binding affinity to a series of oligodeoxyribonucleotides containing either the Sp1-binding site or variants of the G3T sequence. These data indicate that the G3T sequence can interact with Sp1 and that Sp1 may be important in the expression of ADH2. The G3T sequence from the closely related ADH3 gene (encoding gamma gamma-alcohol dehydrogenase) differs from that of ADH2 in the first two nucleotides; it binds both the liver protein and purified Sp1 with lower affinity. This might explain why ADH3 is expressed at lower levels than ADH2 in the liver.

Alcohol Dehydrogenase↗
PubMed1992

The human XIST gene: analysis of a 17 kb inactive X-specific RNA that contains conserved repeats and is highly localized within the nucleus.

X chromosome inactivation in mammalian females results in the cis-limited transcriptional inactivity of most of the genes on one X chromosome. The XIST gene is unique among X-linked genes in being expressed exclusively from the inactive X chromosome. Human XIST cDNAs containing at least eight exons and totaling 17 kb have been isolated and sequenced within the region on the X chromosome known to contain the X inactivation center. The XIST gene includes several tandem repeats, the most 5' of which are evolutionarily conserved. The gene does not contain any significant conserved ORFs and thus does not appear to encode a protein, suggesting that XIST may function as a structural RNA within the nucleus. Consistent with this, fluorescence in situ hybridization experiments demonstrate localization of XIST RNA within the nucleus to a position indistinguishable from the X inactivation-associated Barr body.

Base Sequence↗
PubMed1992

Regulation of human alcohol dehydrogenase genes.

This review focuses upon the regulation of the three human class I alcohol dehydrogenase genes, ADH1, ADH2 and ADH3. These closely related genes are expressed at high levels in liver, and at different levels in other tissues. Multiple cis-acting sequences to which nuclear proteins bind have been mapped, and transcription factors that can bind to these sequences have been identified; these include C/EBP alpha, Sp1, USF, HNF1, CTF/NF1, the glucocorticoid receptor, and RAR alpha. There are interesting but often subtle differences in the binding to these three closely related genes, that presumably account for the differences in patterns of their expression.

Alcohol Dehydrogenase↗
PubMed1992

Effect of including relationships in the estimation of genetic parameters of beef calves.

Variances and covariances for birth weight, gain from birth to weaning (ADG), and 205-d weight were obtained from a sire-dam model and a sire-maternal grandsire model for a herd of Angus and a herd of Hereford cattle. Estimates of direct additive genetic variance (sigma 2A), maternal additive genetic variance (sigma 2M), covariance between direct and maternal additive genetic effects (sigma AM), permanent environmental variance (sigma 2PE), and residual variance (sigma 2e) were obtained both with and without the inverse of the numerator relationship matrix (A-1) included. Estimates of heritability for direct genetic effects (h2A), maternal genetic effects (h2M), and the correlation between direct and maternal effects (rAM) for birth weight were .37, .18, and -.01 in Angus and .53, .23, and -.19 in Herefords, respectively, for the analyses without A-1. For the analyses with A-1, estimates of h2A, h2M, and rAM were .42, .22, and -.12 for Angus and .58, .22, and -.13 for Herefords, respectively. Estimates of h2A, h2M, and rAM for ADG were .43, .15, and -.44 in Angus and .52, .38, and -.03 in Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .57, .15, and -.32 for Angus and .58, .39, and -.05 for Herefords, respectively. Estimates of h2A, h2M, and rAM for 205-d weight were .49, .15, and -.46 for Angus and .58, .43, and -.06 for Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .63, .16, and -.36 for Angus and .66, .43, and -.08 for Herefords, respectively. Estimates of h2A were higher with A-1 than without A-1, but estimates of h2M were similar. Using variances and covariances obtained from analyses including A-1 generally gave higher estimates of direct breeding values than using variances and covariances obtained from analyses not including A-1. Both Pearson product-moment and Spearman rank correlations were high (.99) between estimates of breeding values from the two analyses, although some changes in rank did occur.

Analysis of Variance↗
PubMed1992

Molecular cloning of mouse alcohol dehydrogenase-B2 cDNA: nucleotide sequences of the class III ADH genes evolve slowly even for silent substitutions.

We have cloned and sequenced a cDNA encoding the mouse class III alcohol dehydrogenase, Adh-B2. Adh-B2 mRNA is detectable in all the mouse tissues tested. Class III ADHs are highly conserved: the deduced amino acid sequence of the mouse Adh-B2 is 91 to 97% identical to the human, horse and rat liver enzymes. The mouse Adh-B2 cDNA is 87% identical in nucleotide sequence to the human chi-ADH cDNA. Previously, a slower rate of evolutionary divergence of the amino acid sequences of class III ADH proteins was detected and ascribed to functional constraints upon the protein. Our analysis of the nucleotide sequences demonstrates that this cannot be the entire explanation, since the rate of silent (synonymous) nucleotide substitutions is also lower in the class III ADHs than in the class I ADHs.

Alcohol Dehydrogenase↗
PubMed1991

Four decades of inversion polymorphism in Drosophila pseudoobscura.

We report data that continue the studies of Dobzhansky and others on the frequencies of third-chromosome inversions in natural populations of Drosophila pseudoobscura in North America. The common gene arrangements continue to be present in frequencies similar to those described four decades ago, and the broad geographic patterns also remain unchanged. There is only one pronounced trend over time: the increase in frequency of the Tree Line inversion in Pacific coast populations.

Animals↗
PubMed1991

A gene deleted in Kallmann's syndrome shares homology with neural cell adhesion and axonal path-finding molecules.

Kallmann's syndrome (clinically characterized by hypogonadotropic hypogonadism and inability to smell) is caused by a defect in the migration of olfactory neurons, and neurons producing hypothalamic gonadotropin-releasing hormone. A gene has now been isolated from the critical region on Xp22.3 to which the syndrome locus has been assigned: this gene escapes X inactivation, has a homologue on the Y chromosome, and shows an unusual pattern of conservation across species. The predicted protein has significant similarities with proteins involved in neural cell adhesion and axonal pathfinding, as well as with protein kinases and phosphatases, which suggests that this gene could have a specific role in neuronal migration.

Base Sequence↗
PubMed1991

A gene from the region of the human X inactivation centre is expressed exclusively from the inactive X chromosome.

X-chromosome inactivation results in the cis-limited dosage compensation of genes on one of the pair of X chromosomes in mammalian females. Although most X-linked genes are believed to be subject to inactivation, several are known to be expressed from both active and inactive X chromosomes. Here we describe an X-linked gene with a novel expression pattern--transcripts are detected only from the inactive X chromosome (Xi) and not from the active X chromosome (Xa). This gene, called XIST (for Xi-specific transcripts), is a candidate for a gene either involved in or uniquely influenced by the process of X inactivation.

Base Sequence↗
PubMed1991

Localization of the X inactivation centre on the human X chromosome in Xq13.

X-chromosome inactivation results in the strictly cis-limited inactivation of many but not all genes on one of the two X chromosomes during early development in somatic cells of mammalian females. One feature of virtually all models of X inactivation is the existence of an X-inactivation centre (XIC) required in cis for inactivation to occur. This concept predicts that all structurally abnormal X chromosomes capable of being inactivated have in common a defineable region of the X chromosome. Here we report an analysis of several such rearranged human X chromosomes and define a minimal region of overlap. The results are consistent with models invoking a single XIC and provide a molecular foothold for cloning and analysing the XIC region. One of the markers that defines this region is the XIST gene, which is expressed specifically from inactive, but not active, X chromosomes. The localization of the XIST gene to the XIC region on the human X chromosome implicates XIST in some aspect of X inactivation.

Chromosome Mapping↗
PubMed1991

Inter- and intraobserver reliability of walking-track analysis used to assess sciatic nerve function in rats.

The inter- and intraobserver reliability of the walking-track analysis of sciatic nerve function in the rat was assessed. Twenty-five walking tracks were assessed on three different occasions by four observers. Whereas the interobserver reliability was found to be excellent (r = 0.92), the intraobserver reliability was only satisfactory (r = 0.53 to r = 0.76). Walking-track analysis provides a noninvasive technique to assess function recovery in the rat, with excellent intraobserver reliability demonstrated. The lower intraobserver reliability suggests limitations to this new measurement technique.

Animals↗
PubMed1991

Biofeedback as a means to alter electromyographic activity in a total knee replacement patient.

This paper presents a single case controlled study of a 75-year-old male having bilateral total knee replacement. Baseline EMG recordings demonstrated differential levels of vastus medialis and vastus lateralis muscle activity in both knees during exercise, with increased vastus lateralis activity compared to vastus medialis activity. The purpose of the study was to use electromyographic (EMG) biofeedback training to train the patient to equalize vastus medialis and vastus lateralis EMG activity during exercise. After 11 and 13 training sessions for the left and right knees, respectively, differences between vastus medialis and vastus lateralis activity had markedly decreased. Following the termination of biofeedback training, EMG activity during exercise showed a return toward baseline levels. Several concomitant changes in psychological and physical function were noted. These results suggested that EMG biofeedback can be used to train vastus medialis and vastus lateralis activity in total knee replacement patients, and that biofeedback training may produce positive benefits in other functional areas.

Aged↗
PubMed1991

The 56/58 kDa androgen-binding protein in male genital skin fibroblasts with a deleted androgen receptor gene.

Human genital skin fibroblasts (GSF) make a relatively abundant 56/58 kDa protein that binds androgens. The protein shares many properties with the approximately 100 kDa androgen receptor that is encoded by a locus in the q12 region of the X chromosome. It does not appear to be androgen-induced, yet is absent in GSF of most patients with complete androgen insensitivity (CAI). A precursor-product relation with the androgen receptor (AR) protein has been largely excluded; that it may be an unorthodox product of the AR gene has not. The 56/58 kDa protein is made by the GSF of a mentally retarded subject who has CAI because of a complete deletion of the coding portion of the AR gene. Hence, the strong constitutional and statistical correlations that have been demonstrated between the two proteins cannot arise because they share the same gene. The subject's genomic DNA hybridizes normally with 11 single-copy probes from Xq11-Xq13. Therefore, we cannot attribute her mental retardation to a contiguous gene syndrome.

Androgen-Binding Protein↗