PubMed Health⌕ Search

Biomedical subjects

R L Kelley

Publications and source records attributed to R L Kelley.

At least 19 recordsLinked to original sources
PubMed2006

Energy-dependent excitation cross section measurements of the diagnostic lines of Fe XVII.

By implementing a large-area, gain-stabilized microcalorimeter array on an electron beam ion trap, the electron-impact excitation cross sections for the dominant x-ray lines in the Fe XVII spectrum have been measured as a function of electron energy establishing a benchmark for atomic calculations. The results show that the calculations consistently predict the cross section of the resonance line to be significantly larger than measured. The lower cross section accounts for several problems found when modeling solar and astrophysical Fe XVII spectra.

Journal Article↗
PubMed2003

Laboratory simulation of charge exchange-produced X-ray emission from comets.

In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory.

Journal Article↗
PubMed2001

Association and spreading of the Drosophila dosage compensation complex from a discrete roX1 chromatin entry site.

In Drosophila, dosage compensation is controlled by the male-specific lethal (MSL) complex consisting of MSL proteins and roX RNAs. The MSL complex is specifically localized on the male X chromosome to increase its expression approximately 2-fold. We recently proposed a model for the targeted assembly of the MSL complex, in which initial binding occurs at approximately 35 dispersed chromatin entry sites, followed by spreading in cis into flanking regions. Here, we analyze one of the chromatin entry sites, the roX1 gene, to determine which sequences are sufficient to recruit the MSL complex. We found association and spreading of the MSL complex from roX1 transgenes in the absence of detectable roX1 RNA synthesis from the transgene. We mapped the recruitment activity to a 217 bp roX1 fragment that shows male-specific DNase hypersensitivity and can be preferentially cross-linked in vivo to the MSL complex. When inserted on autosomes, this small roX1 segment is sufficient to produce an ectopic chromatin entry site that can nucleate binding and spreading of the MSL complex hundreds of kilobases into neighboring regions.

Animals↗
PubMed2001

Comparison of fermentation of selected fructooligosaccharides and other fiber substrates by canine colonic microflora.

OBJECTIVE: To compare fermentation characteristics of fructooligosaccharides (FOS) and other fiber substrates that are commonly found in canine diets. SAMPLE POPULATION: Fecal samples from 3 adult dogs. PROCEDURE: The ability of fiber substrates to be used in microbial fermentation reactions was assessed by use of an in vitro fermentation system. Dogs were fed a commercially available food, and feces were collected for use as the microbial inoculum. Substrates used were beet pulp, cellulose, soy fiber, mannanoligosaccharides (MOS), FOS, and 4 inulin products (inulin 1, 2, 3, and 4). Each substrate was incubated anaerobically with fecal inoculum and growth media for 6, 12, and 24 hours, and production of short-chain fatty acids (SCFA) was measured. RESULTS: Total production of SCFA was higher for fermentation of the 4 inulin products and FOS, whereas fermentation of beet pulp, MOS, and soy fiber resulted in moderate concentrations of SCFA. Fermentation of cellulose produced the lowest concentrations of total SCFA without detection of butyrate or lactate. Butyrate production was greatest for fermentation of the 4 inulin products and FOS. Total lactate production was greatest for FOS and inulin 4. As expected, production of SCFA increased for all substrates as fermentation time increased. CONCLUSIONS AND CLINICAL RELEVANCE: Canine fecal microflora ferment FOS-containing substrates in a similar manner, with little fermentation of cellulose-based carbohydrates. Furthermore, results of an in vitro fermentation system indicate that fiber type affects the metabolic activity of microorganisms, thus influencing the amount and nature of the end products of fermentation.

Animals↗
PubMed2000

Ordered assembly of roX RNAs into MSL complexes on the dosage-compensated X chromosome in Drosophila.

BACKGROUND: In the male Drosophila, the X chromosome is transcriptionally upregulated to achieve dosage compensation, in a process that depends on association of the MSL proteins with the X chromosome. A role for non-coding RNAs has been suggested in recent studies. The roX1 and roX2 RNAs are male-specific, non-coding RNAs that are produced by, and also found associated with, the dosage-compensated male X chromosome. Whether roX RNAs are physically part of the MSL complex has not been resolved. RESULTS: We found that roX RNAs colocalize with the MSL proteins and are highly unstable unless the MSL complex is coexpressed, suggesting a physical interaction. We were able to immunoprecipitate roX2 RNA from male tissue-culture cells with antibodies to the proteins Msl1 and Mle, consistent with an integral association with MSL complexes. Localization of roX1 and roX2 RNAs in mutants indicated an order of MSL-complex assembly in which roX2 RNA is incorporated early in a process requiring the Mle helicase. We also found that the roX2 gene, like roX1, is a nucleation site for MSL complex spreading into flanking chromatin in cis. CONCLUSIONS: Our results support a model in which MSL proteins assemble at specific chromatin entry sites (including the roX1 and roX2 genes); the roX RNAs join the complex at their sites of synthesis; and complete complexes spread in cis to dosage compensate most genes on the X chromosome.

Animals↗
PubMed2000

The role of chromosomal RNAs in marking the X for dosage compensation.

Both flies and mammals remodel the architecture of the X chromosome to achieve dosage compensation. A novel class of noncoding RNAs that paint entire chromosomes are centrally involved in this process. The genes encoding these unusual RNAs are themselves located on the X, and are key sites that target the X for dosage compensation.

Animals↗
PubMed2000

A risky business.

Explore the source record for details and available documents.

Emergency Medical Technicians↗
PubMed1999

Epigenetic spreading of the Drosophila dosage compensation complex from roX RNA genes into flanking chromatin.

The multisubunit MSL dosage compensation complex binds to hundreds of sites along the Drosophila single male X chromosome, mediating its hypertranscription. The male X chromosome is also coated with noncoding roX RNAs. When either msl3, mle, or mof is mutant, a partial MSL complex is bound at only approximately 35 unusual sites distributed along the X. We show that two of these sites are the roX1 and roX2 genes and postulate that one of their functions is to provide entry sites for the MSL complex to recognize the X chromosome. The roX1 gene provides a nucleation site for extensive spreading of the MSL complex into flanking chromatin even when moved to an autosome. The spreading can occur in cis or in trans between paired homologs. We present a model for how the dosage compensation complex recognizes X chromatin.

Animals↗
PubMed1999

Specific isoforms of squid, a Drosophila hnRNP, perform distinct roles in Gurken localization during oogenesis.

Heterogeneous nuclear RNA-binding proteins, hnRNPs, have been implicated in nuclear export of mRNAs in organisms from yeast to humans. A germ-line mutation in a Drosophila hnRNP, Squid (Sqd)/hrp40, causes female sterility as a result of mislocalization of gurken (grk) mRNA during oogenesis. Alternative splicing produces three isoforms, SqdA, SqdB, and SqdS. Here we show that these isoforms are not equivalent; SqdA and SqdS perform overlapping but nonidentical functions in grk mRNA localization and protein accumulation, whereas SqdB cannot perform these functions. Furthermore, although all three Sqd isoforms are expressed in the germline cells of the ovary, they display distinct intracellular distributions. Both SqdB and SqdS are detected in germ-line nuclei, whereas SqdA is predominantly cytoplasmic. We show that this differential nuclear accumulation is correlated with a differential association with the nuclear import protein Transportin. Finally, we provide evidence that grk mRNA localization and translation are coupled by an interaction between Sqd and the translational repressor protein Bruno. These results demonstrate the isoform-specific contributions of individual hnRNP proteins in the regulation of a specific mRNA. Moreover, these data suggest a novel role for hnRNPs in localization and translational regulation of mRNAs.

Animals↗
PubMed1997

Sex lethal controls dosage compensation in Drosophila by a non-splicing mechanism.

Dosage compensation in Drosophila requires the male-specific lethal (msl) proteins (MSL) to make gene expression from the single male X chromosome equivalent to that from both female X chromosomes. Expression of ms12 is repressed post-transcriptionally by Sex lethal (SXL), a female-specific RNA-binding protein that regulates alternative splicing in the sex-determination hierarchy. Although msl2 RNA is alternatively spliced in males and females, this does not alter its coding potential and splicing is not required for male-specific expression of MSL2 protein. Instead, our results suggest that the association of SXL protein with multiple sites in the 5' and 3' untranslated regions of the mx12 transcript represses its translation in females. Thus, this well characterized alternative splicing factor regulates at least one target transcript by a distinct mechanism.

Alternative Splicing↗
PubMed1997

Drosophila male-specific lethal-2 protein: structure/function analysis and dependence on MSL-1 for chromosome association.

MSL-2 is required for the male-specific assembly of a dosage compensation regulatory complex on the X chromosome of Drosophila melanogaster. We found that MSL-2 binds in a reproducible, partial pattern to the male X chromosome in the absence of MLE or MSL-3, or when ectopically expressed at a low level in females. Moreover, the pattern of MSL-2 binding corresponds precisely in each case to that of MSL-1, suggesting that the two proteins function together to associate with the X. Consistent with this hypothesis, we isolated EMS-induced loss of function msl-1 and msl-2 alleles in a screen for suppressors of the toxic effects of MSL-2 expression in females. We also used site-directed mutagenesis to determine the importance of the MSL-2 RING finger domain and second cysteine-rich motif. The mutations, including those in conserved zinc coordinating cysteines, confirm that the RING finger is essential for MSL-2 function, while suggesting a less stringent requirement for an intact second motif.

Amino Acid Sequence↗
PubMed1996

Holoprosencephaly in RSH/Smith-Lemli-Opitz syndrome: does abnormal cholesterol metabolism affect the function of Sonic Hedgehog?

The RSH/Smith-Lemli-Opitz syndrome (RSH/SLOS) is an autosomal recessive malformation syndrome associated with increased levels of 7-dehydro-cholesterol (7-DHC) and a defect of cholesterol biosynthesis at the level of 3 beta-hydroxy-steroid-delta7-reductase (7-DHC reductase). Because rats exposed to inhibitors of 7-DHC reductase during development have a high frequency of holoprosencephaly (HPE) [Roux et al., 1979], we have undertaken a search for biochemical evidence of RSH/SLOS and other possible defects of sterol metabolism among patients with various forms of HPE. We describe 4 patients, one with semilobar HPE and three others with less complete forms of the HPE sequence, in whom we have made a biochemical diagnosis of RSH/SLOS. The clinical and biochemical spectrum of these and other patients with RSH/SLOS suggests a role of abnormal sterol metabolism in the pathogenesis of their malformations. The association of HPE and RSH/SLOS is discussed in light of the recent discoveries that mutations in the embryonic patterning gene, Sonic Hedgehog (SHH), can cause HPE in humans and that the sonic hedgehog protein product undergoes autoproteolysis to form a cholesterol-modified active product. These clinical, biochemical, and molecular studies suggest that HPE and other malformations in SLOS may be caused by incomplete or abnormal modification of the sonic hedgehog protein and, possible, other patterning proteins of the hedgehog class, a hypothesis testable in somatic cell systems.

Cells, Cultured↗
PubMed1995

Equality for X chromosomes.

In many species, females possess two X chromosomes and males have one X chromosome. This difference is critical for the initial determination of sex. However, the X encodes many functions required equally in males and females; thus, X chromosome expression must be adjusted to compensate for the difference in dosage between the sexes. Distinct dosage compensation mechanisms have evolved in different species. A common theme in the Drosophila melanogaster and Caenorhabditis elegans systems is that a subtle alteration of chromatin structure may impose this modest, but vital adjustment of the X chromosome transcription level.

Animals↗
PubMed1995

Expression of msl-2 causes assembly of dosage compensation regulators on the X chromosomes and female lethality in Drosophila.

Male-specific lethal-2 (msl-2) is a RING finger protein that is required for X chromosome dosage compensation in Drosophila males. Consistent with the formation of a dosage compensation protein complex, msl-2 colocalizes with the other MSL proteins on the male X chromosome and coimmunoprecipitates with msl-1 from male larval extracts. Ectopic expression of msl-2 in females results in the appearance of the other MSL dosage compensation regulators on the female X chromosomes and decreased female viability. We suggest that msl-2 RNA is the primary target of SxI regulation in the dosage compensation pathway and present a speculative model for the regulation of two distinct modes of dosage compensation by SxI.

Amino Acid Sequence↗