排序方式: 共有63条查询结果,搜索用时 15 毫秒
31.
Tobias Hill Karl JV Nordström Mikael Thollesson Tommy M Säfström Andreas KE Vernersson Robert Fredriksson Helgi B Schiöth 《BMC evolutionary biology》2010,10(1):42
Background
Phylogenetic trees based on sequences from a set of taxa can be incongruent due to horizontal gene transfer (HGT). By identifying the HGT events, we can reconcile the gene trees and derive a taxon tree that adequately represents the species' evolutionary history. One HGT can be represented by a rooted Subtree Prune and Regraft (RSPR) operation and the number of RSPRs separating two trees corresponds to the minimum number of HGT events. Identifying the minimum number of RSPRs separating two trees is NP-hard, but the problem can be reduced to fixed parameter tractable. A number of heuristic and two exact approaches to identifying the minimum number of RSPRs have been proposed. This is the first implementation delivering an exact solution as well as the intermediate trees connecting the input trees. 相似文献32.
33.
34.
Cathrine Hoyo Amy P Murtha Joellen M Schildkraut Randy Jirtle Wendy Demark-Wahnefried Michele R Forman Edwin S Iversen Joanne Kurtzberg Francine Overcash Zhiqing Huang Susan K Murphy 《Epigenetics》2011,6(7):928-936
Folic acid (FA) supplementation before and during pregnancy has been associated with decreased risk of neural tube defects although recent reports suggest it may also increase the risk of other chronic diseases. We evaluated exposure to maternal FA supplementation before and during pregnancy in relation to aberrant DNA methylation at two differentially methylated regions (DMRs) regulating insulin-like growth factor 2 (IGF2) expression in infants. Aberrant methylation at these regions has been associated with IGF2 deregulation and increased susceptibility to several chronic diseases. Using a self-administered questionnaire, we assessed FA intake before and during pregnancy in 438 pregnant women. Pyrosequencing was used to measure methylation at two IGF2 DMRs in umbilical cord blood leukocytes. Mixed models were used to determine relationships between maternal FA supplementation before or during pregnancy and DNA methylation levels at birth. Average methylation at the H19 DMR was 61.2%. Compared to infants born to women reporting no FA intake before or during pregnancy, methylation levels at the H19 DMR decreased with increasing FA intake (2.8%, p = 0.03 and 4.9%, p = 0.04, for intake before and during pregnancy, respectively). This methylation decrease was most pronounced in male infants (p = 0.01). Methylation alterations at the H19 DMR are likely an important mechanism by which FA risks and/or benefits are conferred in utero. Because stable methylation marks at DMRs regulating imprinted genes are acquired before gastrulation, they may serve as archives of early exposures with the potential to improve our understanding of developmental origins of adult disease.Key words: folic acid, epigenetics, IGF2, periconception, prenatal, exposure 相似文献
35.
Nolan CM McCarthy K Eivers E Jirtle RL Byrnes L 《Development genes and evolution》2006,216(3):144-151
The endosome/lysosome system plays key roles in embryonic development, but difficulties posed by inaccessible mammalian embryos
have hampered detailed studies. The accessible, transparent embryos of Danio rerio, together with the genetic and experimental approaches possible with this organism, provide many advantages over rodents.
In mammals, mannose 6-phosphate receptors (MPRs) target acid hydrolases to endosomes and lysosomes, but nothing is known of
acid hydrolase targeting in zebrafish. Here, we describe the sequence of the zebrafish cation-dependent MPR (CD-MPR) and cation-independent
MPR (CI-MPR), and compare them with their mammalian orthologs. We show that all residues critical for mannose 6-phosphate
(M6P) recognition are present in the extracellular domains of the zebrafish receptors, and that trafficking signals in the
cytoplasmic tails are also conserved. This suggests that the teleost receptors possess M6P binding sites with properties similar
to those of mammalian MPRs, and that targeting of lysosomal enzymes by MPRs represents an ancient pathway in vertebrate cell
biology. We also determined the expression patterns of the CD-MPR and CI-MPR during embryonic development in zebrafish. Both
genes are expressed from the one-cell stage through to the hatching period. In early embryos, expression is ubiquitous, but
in later stages, expression of both receptors is restricted to the anterior region of the embryo, covering the forebrain,
midbrain and hindbrain. The expression patterns suggest time- and tissue-specific functions for the receptors, with particular
evidence for roles in neural development. Our study establishes zebrafish as a novel, genetically tractable model for in vivo
studies of MPR function and lysosome biogenesis. 相似文献
36.
Markus Sällman Almén Karl JV Nordström Robert Fredriksson Helgi B Schiöth 《BMC biology》2009,7(1):50-14
Background
Membrane proteins form key nodes in mediating the cell's interaction with the surroundings, which is one of the main reasons why the majority of drug targets are membrane proteins. 相似文献37.
The objectives of this study were to 1) screen all sow herds in a region for M. hyopneumoniae, 2) to effectuate an eradication programme in all those herds which were shown to be infected with M. hyopneumoniae, and 3) to follow the success of the screening and the eradication programmes. The ultimate goal was to eradicate M. hyopneumoniae from all member herds of a cooperative slaughterhouse (153 farrowing herds + 85 farrowing-to-finishing herds + 150 specialised finishing herds) before year 2000. During 1998 and 1999, a total of 5067 colostral whey and 755 serum samples (mean, 25 samples/herd) were collected from sow herds and analysed for antibodies to M. hyopneumoniae by ELISA. Antibodies were detected in 208 (3.6%) samples. Two farrowing herds (1.3%) and 20 farrowing-to-finishing herds (23.5%) were shown to be infected with M. hyopneumoniae. A programme to eradicate the infection from these herds was undertaken. During March 2000, a survey was made to prove the success of the screening and the eradication programmes. In total, 509 serum samples were collected randomly from slaughtered finishing pigs. Antibodies to M. hyopneumoniae were not detected in 506 of the samples, whereas 3 samples were considered suspicious or positive. Accordingly, 3 herds were shown to be infected. One of the herds was previously falsely classified as non-infected. Two of the herds were finishing herds practising continuous flow system (CF). Unlike finishing herds which practice all-in/all-out management routines on herd level, CF herds do not get rid of transmissible diseases spontaneously between batches, for which reason a screening was made in the rest of the CF herds (total n = 7). Consequently, 2 more infected herds were detected. In addition to the results of the survey, a decreasing prevalence of lung lesions at slaughter (from 5.2% to 0.1%) and lack of clinical breakdowns indicated that all member herds were finally free from M. hyopneumoniae in the end of year 2000. 相似文献
38.
Imprint status of M6P/IGF2R and IGF2 in chickens 总被引:4,自引:0,他引:4
Catherine M. Nolan J. Keith Killian James N. Petitte Randy L. Jirtle 《Development genes and evolution》2001,211(4):179-183
Genomic imprinting is a method of gene regulation whereby a gene is expressed in a parent-of-origin-dependent fashion; however, it is hypothesized that imprinting should not occur in oviparous taxa such as birds. Therefore, we examined the allelic expression of two genes in the chicken that are reciprocally imprinted in most mammals, mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) and insulin-like growth factor 2 (IGF2). Single nucleotide polymorphisms were identified in these genes, and cDNA was prepared from several tissues of embryos heterozygous for these polymorphisms. Both alleles of M6P/IGF2R and IGF2 were expressed in all tissues examined by RT-PCR. Since the expression of these genes was independent of the parent from which they were inherited, we conclude that neither M6P/IGF2R nor IGF2 are imprinted in the chicken. 相似文献
39.
Abnormal postnatal maintenance of elevated DLK1 transcript levels in callipyge sheep 总被引:6,自引:0,他引:6
Susan K. Murphy Brad A. Freking Timothy P.L. Smith Kreg Leymaster Catherine M. Nolan Andrew A. Wylie Heather K. Evans Randy L. Jirtle 《Mammalian genome》2005,16(3):171-183
The underlying mechanism of the callipyge muscular hypertrophy phenotype in sheep (Ovis aries) is not presently understood. This phenotype, characterized by increased glycolytic type II muscle proportion and cell size accompanied by decreased adiposity, is not visibly detectable until approximately three to eight weeks after birth. The muscular hypertrophy results from a single nucleotide change located at the telomeric end of ovine Chromosome 18, in the region between the imprinted MATERNALLY EXPRESSED GENE 3 (MEG3) and DELTA, DROSOPHILA, HOMOLOG-LIKE 1 (DLK1) genes. The callipyge phenotype is evident only when the mutation is paternally inherited by a heterozygous individual. We have examined the pre- and postnatal expression of MEG3 and DLK1 in sheep of all four possible genotypes in affected and unaffected muscles as well as in liver. Here we show that the callipyge phenotype correlates with abnormally high DLK1 expression during the postnatal period in the affected sheep and that this elevation is specific to the hypertrophy-responsive fast-twitch muscles. These results are the first to show anomalous gene expression that coincides with both the temporal and spatial distribution of the callipyge phenotype. They suggest that the effect of the callipyge mutation is to interfere with the normal postnatal downregulation of DLK1 expression. 相似文献
40.
A small fraction of the genome contains genes that are imprinted and thus expressed exclusively from one parental allele.We report here that the human neuronatin gene (NNAT) on chromosome 20q11.2 is imprinted and transcribed specifically from the paternal allele. The region containing NNAT has multiple CpG islands, and methylation analysis showed that a 1.8-kb CpG island in its promoter region exhibits differential methylation in all tissues examined. This finding is consistent with the island acting as a component of the NNAT imprint control domain. NNAT lies within the singular 8.5-kb intron of the gene encoding bladder cancer-associated protein (BLCAP), which, as we demonstrate, is not imprinted. This study provides the first example, to our knowledge, in humans of an imprinted gene contained within the genomic structure of a nonimprinted gene. Thus, NNAT is in an imprinted "microdomain," making this locus uniquely suited for the investigation of mechanisms of localized imprint regulation. 相似文献