PubMed Health⌕ Search

Biomedical subjects

S L Mansour

Publications and source records attributed to S L Mansour.

13 recordsLinked to original sources
PubMed2001

Impaired motor coordination in mice that lack punc.

The punc gene, encoding a member of the neural cell adhesion molecule family expressed in the developing central nervous system, limbs, and inner ear, was identified. To extend studies of the normal expression pattern of punc and to determine its function, a mouse strain bearing a lacZ/neo insertion in a 5' coding exon was created. The complex pattern of punc expression in embryos from embryonic day 9.5 (E9.5) to E11.5 was mimicked accurately by beta-galactosidase (beta-Gal) activity. As development proceeded, the distribution of beta-Gal activity was increasingly restricted, finally becoming confined to the brain and inner ear by E15.5. In the adult, beta-Gal activity was detected in several regions of the inner ear and brain and was particularly strong in the cerebellar Bergmann glia. Genetic analysis of this null allele demonstrated that punc is not required for normal embryogenesis. Interestingly, comparisons of beta-Gal activity and punc transcripts in heterozygous and homozygous mutant individuals demonstrated that punc is negatively autoregulated in some tissues. Adult punc-deficient mice were overtly normal and had normal hearing. Compared with control littermates, however, homozygous mutants had significantly reduced retention times on the Rotarod, suggesting a role for Bergmann glia-expressed Punc in the cerebellar control of motor coordination.

Amino Acid Sequence↗
PubMed2000

Defective organellar membrane protein trafficking in Ap3b1-deficient cells.

AP-3 is a heterotetrameric protein complex involved in intracellular vesicle transport. Molecular analyses show that Ap3b1, which encodes the AP-3 (&bgr;)3A subunit, is altered in pearl mice. To provide genetic evidence that mutation of Ap3b1 is responsible for the pearl phenotype and to determine the null phenotype, the Ap3b1 gene was disrupted by homologous recombination. Mice homozygous for the resulting allele, Ap3b1(LN), or compound heterozygotes with pearl, displayed phenotypes similar to those of pearl mice, confirming that Ap3b1 is the causal gene for pearl. Moreover, pearl is likely to be a hypomorph as the Ap3b1(LN) homozygotes had a lighter coat color and accumulated fewer of the micro3 and (&dgr;)3 subunits of AP-3 than did pearl mice. Finally, immunofluorescence analysis of fibroblasts and melanocytes cultured from Ap3b1(LN) homozygotes revealed that the lysosomal membrane proteins Lamp I and Lamp II and the melanosomal membrane protein tyrosinase were mislocalized. In particular, the Lamp proteins were clustered on the cell surface. These findings strengthen the evidence for an alternate pathway via the plasma membrane for cargo normally transported to organelles by AP-3.

Adaptor Protein Complex 3↗
PubMed1999

Expression and genetic analysis of prtb, a gene that encodes a highly conserved proline-rich protein expressed in the brain.

A mouse gene, designated prtb (proline codon-rich transcript, brain expressed) was identified and characterized from a gene trap embryonic stem cell line. It encodes a proline-rich protein of 168 amino acids that shares 99% amino acid sequence identity with its human homologue and is located on the distal region of mouse chromosome 15. To determine the expression pattern and function of prtb, mice that carry the prtb(gt) allele were generated. During embryogenesis,prtb gene expression as revealed by beta-galactosidase (beta-gal) marker gene activity was highly regulated. Between embryonic day (E) 11.5 and E12.5, beta-gal activity was restricted to the developing heart. From E13.5 on, expression in the heart was extinguished. However, very strong beta-gal activity could be detected in the brains of adult mice, suggesting a role for this gene in brain function. Mice homozygous for the mutation were viable, fertile, and did not display any obvious abnormalities. This could be due to functional redundancy as Northern blot hybridization analysis clearly demonstrated that prtb(gt) is likely to be a null allele.

5' Untranslated Regions↗
PubMed1997

Trapping genes expressed in the developing mouse inner ear.

Identification of the genes involved in the development of the mouse inner ear and developmental studies of mice that bear mutations in these genes is an important approach to understanding genetically determined human auditory dysfunction. Towards this end, we initiated a gene trap screen designed to simultaneously mark and mutate genes in mouse embryonic stem cells by the insertion of a lacZ reporter gene. Expression of beta-galactosidase in gene trap cell lines was monitored both before and after the addition of factors that are known to affect inner ear development. Gene trap cell lines that expressed beta-galactosidase under one or more culture conditions were used to create chimeric mouse embryos for studies of reporter gene expression in vivo. A high proportion of these gene trap insertions were expressed in the developing inner ear, suggesting that this strategy provides an effective means of identifying genes that may be involved in inner ear development or function.

Animals↗
PubMed1994

Targeted disruption of int-2 (fgf-3) causes developmental defects in the tail and inner ear.

The int-2 gene (also designated fgf-3) was originally identified because its transcription is activated by the nearby integration of mouse mammary tumor virus in virus-induced tumors. Molecular analyses have revealed that the int-2 gene produces at least four mRNAs, all of which encode a protein that has 40-50% amino acid sequence similarity with the fibroblast growth factors (FGFs). Int-2 gene expression is localized to a small number of discrete sites in the developing mouse, but has not been detected in any nonneoplastic adult tissue. The expression data and the amino acid sequence similarity with the FGFs suggested several potential roles for int-2 during normal development. To evaluate these possibilities, we initiated a genetic analysis of int-2. A gene-targeting protocol was used to generate embryonic stem (ES) cells that are heterozygous for an insertion of the neo(r) gene into the first protein-coding exon of int-2. These cells were used to establish a line of mice that carry the gene disruption. Animals that are heterozygous for the int-2neo allele are normal and fertile. Homozygous mutants survive embryonic development and can be visually identified after 12.5 days of gestation by a short, initially dorsally curled tail. This defect is potentially due to the disruption of int-2 expression in the primitive streak/tail bud. Most of the homozygous mutants die at or soon after birth, but several have survived to adulthood. In addition to the tail phenotype, the surviving homozygotes show, to varying extents, symptoms characteristic of inner ear abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1993

Mice homozygous for a targeted disruption of the proto-oncogene int-2 have developmental defects in the tail and inner ear.

We derived mice that carry a targeted insertion of a neor gene in the int-2 (Fgf-3) proto-oncogene coding sequences. The mutation was found to be recessive and mice that were homozygous for the insertion did not often survive to adulthood. The mutant mice had defects in the development of the tail and inner ear that could be correlated with disruption of int-2 expression in the posterior primitive streak and hindbrain or otic vesicle. While the tail phenotype was 100% penetrant, we found that the inner ear phenotype had reduced penetrance and variable expressivity. The variable expressivity could not be attributed to variability in the genetic background of the mutant allele or to leaky expression from the mutant allele. Thus, we conclude that even in a uniform genetic background, stochastic variation in the expression of a developmental circuit can result in dramatic differences in phenotypic consequences.

Animals↗
PubMed1990

Gene targeting in murine embryonic stem cells: introduction of specific alterations into the mammalian genome.

The ability to create targeted mutations in the mouse will have an impact on many areas of research in mammalian biology. Mutations are generated in embryonic stem (ES) cells by homologous recombination between exogenously added DNA and the endogenous chromosomal sequences. These cells are then used to generate chimeric intermediates that pass the mutant allele through the germ line, initiating a strain of mice that carry the desired mutation. This review focuses on the selection of a starting ES cell line, introduction of DNA into ES cells, construction of gene targeting vectors, and selection/enrichment schemes for the isolation of targeted cell lines. The generation of mice that carry the targeted allele is briefly outlined.

Animals↗
PubMed1990

Introduction of a lacZ reporter gene into the mouse int-2 locus by homologous recombination.

We demonstrate that the frequency of gene targeting is unaffected by the length of nonhomologous DNA transferred to a target chromosomal sequence. A result of this finding is that a much wider spectrum of designed genomic alterations is now feasible. As a first application, we inserted a 5.4-kilobase cassette of nonhomologous DNA into the int-2 locus in mouse embryo-derived stem cells by gene targeting. The inserted DNA contained a lacZ gene positioned to create an in-frame fusion with the int-2 protein-coding region. Upon differentiation of these cells to embryoid bodies, the int-2-lacZ fusion faithfully reproduced the expression pattern of int-2 RNA. This ability to target reporter genes, such as lacZ, to specific mouse loci, combined with the ability to move the tagged gene into different mutant backgrounds, may provide an ideal approach for analyzing interactions among genes that participate in a developmental network.

Animals↗
PubMed1988

Disruption of the proto-oncogene int-2 in mouse embryo-derived stem cells: a general strategy for targeting mutations to non-selectable genes.

Gene targeting--homologous recombination of DNA sequences residing in the chromosome with newly introduced DNA sequences--in mouse embryo-derived stem cells promises to provide a means to generate mice of any desired genotype. We describe a positive nd negative selection procedure that enriches 2,000-fold for those cells that contain a targeted mutation. The procedure was applied to the isolation of hprt- and int-2- mutants, but it should be applicable to any gene.

Animals↗
PubMed1988

Four classes of mRNA are expressed from the mouse int-2 gene, a member of the FGF gene family.

Mouse embryos at 7.5 days of gestation and endodermal cells derived from embryonal carcinoma cells each express four int-2 mRNAs of similar size and relative abundance. To determine their structure and coding potential, we prepared a cDNA library from endoderm mRNA and isolated several int-2 cDNAs. Structural analysis of these cDNAs combined with Northern blot hybridization and primer extension analyses of int-2 mRNA revealed that the differences between the mRNAs are generated through the use of two alternate transcriptional start sites and two alternate polyadenylation sites. All four mRNAs share a common core sequence that encodes a protein with amino acid similarity to fibroblast growth factor.

Amino Acid Sequence↗
PubMed1986

Downstream sequences affect transcription initiation from the adenovirus major late promoter.

We analyzed a set of adenovirus-simian virus 40 (SV40) hybrids in which the SV40 T antigen coding sequences are inserted downstream from the adenovirus major late promoter within the first, second, and third segments of the tripartite leader. In infected cells, these viruses give rise to a matched set of hybrid SV40 mRNAs that differ only in the number of tripartite leader segments attached to the complete SV40 T antigen coding region. We found that the number of tripartite leader segments present at the 5' end of the hybrid SV40 mRNAs had little effect on the efficiency of T antigen translation. Surprisingly, insertion of SV40 sequences within the first leader segment, at +33 relative to the start of transcription, significantly reduced the frequency of transcription initiation from the major late promoter. The 3' boundary of this downstream transcriptional control element was mapped between +33 and +190 by showing that insertion of SV40 sequences within the intron after the first leader segment at +190 had very little effect on transcription initiation from the late promoter. A transient expression assay was used to show that the effect of downstream sequences on transcription initiation from the major late promoter is dependent on a trans-acting factor encoded or induced by adenovirus.

Adenoviridae↗
PubMed1985

An adenovirus vector system used to express polyoma virus tumor antigens.

We have used a generalized adenovirus vector system to express the three polyoma tumor (T) antigen proteins under the control of the adenovirus major late promoter. One hybrid virus, Ad-PySVR498, expresses high levels of polyoma middle and small T antigens. A second hybrid virus, Ad-LTSVR545, which contains a cDNA copy of the polyoma A gene, overproduces large T antigen. The T antigens produced are indistinguishable from their authentic polyoma counterparts as determined by immunoprecipitation and partial cleavage by V8 protease. Analysis of polyoma mRNAs encoded by the recombinant viruses showed that they initiate from the adenovirus major late promoter and contain the tripartite leader at their 5' ends. Large T antigen isolated from Ad-LTSVR545-infected cells by immunoaffinity was shown to bind selectively to polyoma DNA sequences that contain the origin of viral DNA replication as well as the sites for transcription initiation.

Adenoviridae↗