Search PubMed⌕ Search

Biomedical subjects

L M Silver

Publications and source records attributed to L M Silver.

At least 127 records · Page 7Linked to original sources
PubMed1982

Genomic analysis of the H-2 complex region associated with mouse t haplotypes.

Naturally occurring t haplotypes suppress recombination over a region of mouse chromosome 17 that includes the H-2 complex. Each of these t haplotypes is associated with a specific set of H-2 alleles and can be placed into one of a limited number of complementation groups. Genetic studies have demonstrated the existence of a basic homology in genomic organization among all t haplotypes. We used an H-2 cDNA probe to investigate, at the molecular level, possible relationships among the H-2 regions of different t haplotypes. We identified a family of t haplotype-specific restriction fragments that carry DNA sequences homologous to the H-2-like genes. Surprisingly, the H-2-defined restriction patterns from all five complete t haplo-types analyzed are highly homologous, even though H-2 gene products expressed are antigenically distinct. These data lead to two major conclusions. First, all t haplotypes were derived from a small number of closely related ancestors. Second, the H-2 complex region associated with each primordial t chromosome has been maintained within at least the five present-day t haplotypes analyzed here. Hence the H-2 complex is an integral component of naturally occurring t haplotypes.

Animals↗
PubMed1981

Recombination suppression of mouse t-haplotypes due to chromatin mismatching.

We show here that recombination occurs at the normal rate in compound female mice containing two different complementing lethal haplotypes (th17/tw12) where there is a long stretch of homologous t-mutant chromatin. Thus the recombination suppression of a complete t-haplotype cannot be due to an intrinsic factor(s) which suppresses along the length of its own chromosome but is due to 'mismatching' of wild-type and mutant chromatin. Naturally occurring t-haplotypes of mouse chromosome 17 have several interesting genetic properties. First, they are always transmitted from males in much higher proportions than mendelian expectation; presumably this accounts for the maintenance of lethal and semilethal t-haplotypes at polymorphic levels in populations of wild mice. t-Haplotypes also show recombination suppression. The conventional map distance between genetic markers T and tf is 7-12 cM, whereas in (t/+) heterozygotes for naturally occurring t-haplotypes, recombination is suppressed and T and tf seem to be separated by only 0.1-0.5 cM (ref. 1). The region of recombination suppression extends to and includes the major histocompatibility complex (H-2). Thus t and H-2 effectively travel as a single unit-- a 'super gene'. Although recombination suppression is known to be accompanied by failure of chiasmata formation, the mechanism underlying the suppression has remained an enigma. Lyon suggested a disorder of t-heterochromatin and more recently a change in 'intercalary' middle repetitive DNA. She proposed that either t-chromatin is intrinsically incapable of participating in crossing-over, or chiasma formation is prevented because of mismatching and mispairing of normal and abnormal chromatin. We have measured recombinant between two chromosomes which carried extensive overlapping segments of t-chromatin. We report here that in this configuration, recombination occurs at a normal rate, and thus we conclude that cross-over suppression is due to mismatching.

Animals↗
PubMed1981

Distribution studies on polytene chromosomes using antibodies directed against hnRNP.

The distribution of nuclear ribonucleoprotein (hnRNP) particles in Drosophila polytene chromosomes has been investigated using anti-B-36 serum as a probe. The use of polytene chromosomes allows resolution at the level of the chromomere, and provides the opportunity to look for both positive and negative correlations with transcriptional activity. The antiserum was obtained using the nuclear protein B-36 from Physarum polycephalum as the immunogen. It has been shown to precipitate hnRNP particles from HeLa cells through a cross-reaction with the major 32,000- and 34,000-dalton hnRNP particle proteins. The antiserum cross-reacts with a Drosophila nuclear protein of approximately 34,000 daltons. By indirect immunofluorescence, we observed that the antiserum reacts preferentially with transcriptionally active loci of the polytene chromosomes, whereas loci previously or subsequently active do not show significant fluorescence. The overall pattern of fluorescence is very similar to that generated with anti-RNA polymerase B serum. The correlation of fluorescence and transcriptional activity observed suggests that the anti-B-36 serum is recognizing hnRNP proteins which have combined with nascent RNA molecules at the sites of transcription.

Animals↗
PubMed1980

Molecular analysis of the genetic relationship of trans interacting factors at the T/t complex.

The T/t complex is an extensive genetic region proximal to the H-2 complex on mouse chromosome 17, with multiple effects on embryonic development, spermatogenesis and recombination. Recently, two-dimensional gel analysis of testicular cell proteins identified a gene within the T/t complex that codes for a major cell surface-associated protein, p63/6.9 (ref. 4). The wild-type gene, Tcp-1b, codes for a 63,000-molecular weight protein (p63/6.9b), whereas a mutant allele, Tcp-1a, which occurs in all intact t haplotypes, codes for a more acidic form of the protein (p63/6.9a). Analysis of partial t haplotypes obtained from rare recombination events showed that Tcp-1a correlated completely with the tail interaction factor tT, which is thought to be a genetic allele of T, thus raising the possibility that the locus of T codes for the p63/6.9 protein. We report here that the p63/6.9 proteins produced by seven chromosomes carrying independently derived dominant mutations at the locus of T are all indistinguishable from the wild-type form; thus, the cumulative data indicate that the Tcp-1 gene is most probably not at the locus of T.

Animals↗
PubMed1980

Cell-free translation of a T/t complex cell surface-associated gene product.

The p63/6.9 protein has previously been shown to be specified by a gene within the mouse T/t complex. All wild-type chromosomes 17 specify a basic form of p63/6.9 (p63/6.9b). It is distinguishable by two-dimensional gel electrophoresis from the acidic form of p63/6.9 (p63/6.9a), which is specified by all complete t haplotypes analyzed to date. To determine whether p63/6.9 is a direct gene product of the T/t complex, testicular cytoplasmic RNA from mice bearing the genotypes +/+, +/t and t/t was translated in a rabbit reticulocyte-derived cell-free system, and translated products were analyzed by two-dimensional gel electrophoresis. The data indicate that the difference between th allelic forms of p63/6.9 is encoded within mRNA transcribed from the T/t complex. Thus p63/6.9 is the first primary gene product identified in the T/t complex. Results obtained from both cell-free translation and pulse-chase labeling experiments indicate that the mature cell surface-associated form of p63/6.9 has not undergone detectable post-translational modification.

Alleles↗
PubMed1980

Evidence for unequal crossing over within the mouse T/t complex.

The Tcp-1 gene located within the T/t complex on chromosome 17 of the mouse codes for a major cell surface-associated protein p63/6.9. Previously, we identified two structural alleles of this gene which specify alternate forms of the p63/6.9 protein. The Tcp-1b allele is associated with all wild-type chromosome 17; the Tcp-1a allele is found only with chromosome 17 carrying a complete t haplotype. Normal recombination along a major length of chromosome 17 is suppressed in mice that are heterozygous for any complete t haplotype. Suppression is not complete, however, and rare crossing over between wild-type and t haplotype chromatin does occur. In this report, 15 rare recombinant chromosomes have been analyzed for Tcp-1 alleles. The results indicate that in four independent events the Tcp-1b and Tcp-1a alleles have become associated in cis position in a single DNA molecule. Further genetic analysis provides support for the hypothesis that a significant nonhomology exists between the arrangement of DNA sequences on wild-type and t-carrying chromosome 17. This could account for both the suppression of normal recombination along the stretch of t chromatin and the frequent unequal crossing over when rare recombinational events do take place.

Alleles↗
PubMed1978

Production and characterization of antisera against three individual NHC proteins; a case of a generally distributed NHC protein.

In order to assess the selectivity of the distribution patterns of individual nonhistone chromosomal proteins (NHC proteins), immunofluorescent staining experiments were performed on Drosophila polytene chromosomes. Antisera have been prepared against three individual NHC proteins which were isolated by sequential preparative slab gel isoelectric focusing and SDS polyacrylamide gel electrophoresis. In two cases, immunofluorescent staining of the chromosomes indicated a specific limited distribution pattern; apparently the antigen in each case is present at a reproducible and distinct subset of chromomeres. This type of pattern has also been obtained with antisera prepared against molecular weight subfractions of NHC proteins (Silver and Elgin, 1977). Each selective fluorescence distribution pattern obtained so far is reproducible and unique to the antiserum under study. In a third case, an antiserum caused prominant staining at dense chromomeres and the chromocenter in a pattern mimicking DNA (and presumably histone) distribution. Indirect radioimmunostaining of SDS and isoelectric focusing gels on which total NHC proteins had been separated confirmed that this antiserum reacted specifically with a protein(s) of molecular weight 21,000 D and pI 5.2. The data in conjunction with absorption experiments indicates that the chromosomal staining is due to an interaction of antibodies with NHC protein(s) and not with histones. This finding suggests that at least one major acidic NHC protein plays a very general role (comparable to that of the histones) in maintaining chromatin structure.

Animals↗
PubMed1978

A protein released by DNAase I digestion of drosophila nuclei is preferentially associated with puffs.

Antisera have been produced against five molecular weight subfractions of the Drosophila proteins readily extracted from nuclei following limited DNAase I digestion. Immunofluorescence staining techniques were used to assess the distributions of these proteins in the polytene chromosomes of Drosophila. In three cases, the antigens were widely distributed; in one case, the antigens appeared to be slightly more concentrated at active loci; and in one case, the antigens were strongly concentrated at a defined set of loci, including puffs and most of the loci which are active (puffed) at some time during third instar larval and prepupal development. The latter distribution pattern differs from that of RNA polymerase. Nonhistone chromosomal proteins of this type may have a key role in establishing and/or maintaining the altered chromatin structure characteristic of the active state.

Animals↗
PubMed1976

A method for determination of the in situ distribution of chromosomal proteins.

A technique has been developed for "staining" cytological preparations by indirect immunofluorescent methods that permits determination of the in situ distribution of chromosomal proteins. The method is particularly oriented to the use of polytene chromosome squashes from Drosophila salivary glands. Control experiments indicate that the fixation methods used allow little or no extraction or rearrangement of the chromosomal proteins. The results obtained demonstrate the specific in vivo chromosomal locations of nonhistone proteins purified from isolated chromatin. The technique is apparently capable of resolution at the level of the chromomere or band, the unit of genetic organization in Drosophila.

Animals↗
PubMedDate not supplied

Necrotizing fasciitis in the lower extremity: a review and case presentation.

Necrotizing fasciitis is a rare but potentially fatal disease which is often confused with cellulitis. By examining the pathogenesis, clinical presentation, treatment, and a representative case study, this article proposes to lend a broader perspective to this infection. Emphasis is placed on the necessity of surgical debridement in combination with antibiotic therapy to minimize the possible morbidity associated with this condition.

Anti-Bacterial Agents↗