983 resultados para Nuclear genes


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A multisubunit form of acetyl coenzyme A (CoA) carboxylase (ACCase) from soybean (Glycine max) was characterized. The enzyme catalyzes the formation of malonyl CoA from acetyl CoA, a rate-limiting step in fatty acid biosynthesis. The four known components that constitute plastid ACCase are biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and the α- and β-subunits of carboxyltransferase (α- and β-CT). At least three different cDNAs were isolated from germinating soybean seeds that encode BC, two that encode BCCP, and four that encode α-CT. Whereas BC, BCCP, and α-CT are products of nuclear genes, the DNA that encodes soybean β-CT is located in chloroplasts. Translation products from cDNAs for BC, BCCP, and α-CT were imported into isolated pea (Pisum sativum) chloroplasts and became integrated into ACCase. Edman microsequence analysis of the subunits after import permitted the identification of the amino-terminal sequence of the mature protein after removal of the transit sequences. Antibodies specific for each of the chloroplast ACCase subunits were generated against products from the cDNAs expressed in bacteria. The antibodies permitted components of ACCase to be followed during fractionation of the chloroplast stroma. Even in the presence of 0.5 m KCl, a complex that contained BC plus BCCP emerged from Sephacryl 400 with an apparent molecular mass greater than about 800 kD. A second complex, which contained α- and β-CT, was also recovered from the column, and it had an apparent molecular mass of greater than about 600 kD. By mixing the two complexes together at appropriate ratios, ACCase enzymatic activity was restored. Even higher ACCase activities were recovered by mixing complexes from pea and soybean. The results demonstrate that the active form of ACCase can be reassembled and that it could form a high-molecular-mass complex.

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Simple phylogenetic tests were applied to a large data set of nucleotide sequences from two nuclear genes and a region of the mitochondrial genome of Trypanosoma cruzi, the agent of Chagas' disease. Incongruent gene genealogies manifest genetic exchange among distantly related lineages of T. cruzi. Two widely distributed isoenzyme types of T. cruzi are hybrids, their genetic composition being the likely result of genetic exchange between two distantly related lineages. The data show that the reference strain for the T. cruzi genome project (CL Brener) is a hybrid. Well-supported gene genealogies show that mitochondrial and nuclear gene sequences from T. cruzi cluster, respectively, in three or four distinct clades that do not fully correspond to the two previously defined major lineages of T. cruzi. There is clear genetic differentiation among the major groups of sequences, but genetic diversity within each major group is low. We estimate that the major extant lineages of T. cruzi have diverged during the Miocene or early Pliocene (3–16 million years ago).

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Stress-induced mutations may play an important role in the evolution of plants. Plants do not sequester a germ line, and thus any stress-induced mutations could be passed on to future generations. We report a study of the effects of heat shock on genomic components of Brassica nigra Brassicaceae. Plants were submitted to heat stress, and the copy number of two nuclear-encoded single-copy genes, rRNA-encoding DNA (rDNA) and a chloroplast DNA gene, was determined and compared to a nonstressed control group. We determined whether genomic changes were inherited by examining copy number in the selfed progeny of control and heat-treated individuals. No effects of heat shock on copy number of the single-copy nuclear genes or on chloroplast DNA are found. However, heat shock did cause a statistically significant reduction in rDNA copies inherited by the F1 generation. In addition, we propose a DNA damage-reppair hypothesis to explain the reduction in rDNA caused by heat shock.

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To examine whether mtDNA is uni- or biparentally transmitted in mice, we developed an assay that can detect sperm mtDNA in a single mouse embryo. In intraspecific hybrids of Mus musculus, paternal mtDNA was detected only through the early pronucleus stage, and its disappearance co-incided with loss of membrane potential in sperm-derived mitochondria. By contrast, in interspecific hybrids between M. musculus and Mus spretus, paternal mtDNA was detected throughout development from pronucleus stage to neonates. We propose that oocyte cytoplasm has a species-specific mechanism that recognizes and eliminates sperm mitochondria and mtDNA. This mechanism must recognize nuclearly encoded proteins in the sperm midpiece, and not the mtDNA or the proteins it encodes, because sperm mitochondria from the congenic strain B6.mtspr, which carries M. spretus mtDNA on background of M. musculus (B6) nuclear genes, were eliminated early by B6 oocytes as in intraspecific crosses. We conclude that cytoplasmic genomes are transmitted uniparentally in intraspecific crosses in mammals as in Chlamydomonas and that leakage of parental mtDNA is limited to interspecific crosses, which rarely occur in nature.

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The level and structure of yeast iso-1-cytochrome c and iso-2-cytochrome c, encoded by the nuclear genes CYC1 and CYC7, respectively, are normally not altered in rho- mutants, which completely lack the cytochromes a.a3 subunits and cytochrome b that are encoded by mitochondrial DNA. In contrast, iso-cytochromes c containing the amino acid change Thr-78-->Ile (T78I) were observed at the normal or near-normal wild-type level in rho+ strains but were completely absent in rho- mutants. We have demonstrated with the "global" suppressor mutation Asn-52-->Ile and by pulse-chase labeling that the T78I iso-1-cytochrome c undergoes rapid cellular degradation in rho- mutants. Furthermore, specific mutations revealed that the deficiency of T78I iso-1 cytochrome c can be caused by the lack of cytochrome a.a3 or cytochrome c1, but not by the lack of cytochrome b. Thus, this and certain other, but not all, labile forms of cytochrome c are protected from degradation by the interaction with its physiological partners.

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A diversidade de espécies e fenotípica pode variar consideravelmente entre grupos taxonômicos e ao longo do tempo em uma mesma linhagem. O estudo de tais variações tornou-se um dos principais objetivos da biologia evolutiva fornecendo informações importantes a respeito dos possíveis mecanismos que regulam a biodiversidade. Dessa forma, o objetivo geral da presente tese foi investigar os padrões da diversificação de espécies e da morfologia em um grupo cosmopolita de serpentes, a família Viperidae, e os potenciais processos subjacentes. Primeiramente, (1) reconstruímos as relações filogenéticas e estimamos os tempos de divergência entre as linhagens da família Viperidae utilizando uma abordagem Bayesiana. (2) Aplicando um método recentemente desenvolvido (BAMM), exploramos como as taxas de especiação e extinção variaram ao longo da radiação do grupo inferindo os possíveis processos reguladores. Por fim, (3) analisamos se a evolução do tamanho do corpo e as taxas de especiação variam nos diferentes habitats ocupados pelos viperídeos (terrestres vs arborícola). Nesta tese geramos a filogenia molecular de viperídeos mais completa até o momento utilizando sequências para 11 genes mitocondriais e nucleares abrangendo 79% das espécies viventes (264 terminais) e todos com exceção de um gênero. De maneira geral, foi possível obter relações filogenéticas robustas para o grupo com a maioria dos gêneros sendo monofilética. Os tempos de divergência obtidos indicam que os viperídeos começaram a diversificar em meados do Paleoceno tardio/meio do Eoceno inferindo idades um pouco mais tardias que o encontrado em estudos anteriores. Durante a radiação do grupo, um aumento nas taxas de especiação parece ter ocorrido durante a diversificação dos crotalíneos (pit vipers) em decorrência não só da evolução das fossetas loreais mas também como resultado de mudanças geológicas e climáticas na Ásia e da invasão do novo mundo. Após este rápido aumento inicial, as taxas de especiação desaceleraram em direção ao presente. Por fim, os resultados aqui apresentados indicam que apesar dos habitats arborícolas limitarem a evolução morfológica nos viperídeos, a evolução da arborealidade parece não afetar as taxas de especiação que permanecem similares entre linhagens arborícolas e terrestres. Isto sugere dois cenários: (1) a especiação acontece de forma independente das mudanças morfológicas nos viperídeos; ou (2) o isolamento geográfico seria um mecanismo importante na diversificação de linhagens arborícolas contrabalançando decréscimos nas oportunidades de especiação possivelmente relacionados às pressões seletivas impostas pelo ambiente arborícola. A presente tese contribui para entendermos mais sobre como evoluíram os viperídeos ao longo dos seus ∼50 milhões de anos. Além de propor cenários e hipóteses a serem futuramente explorados com os viperídeos, elaboramos uma discussão ampla e conceitual a respeito dos possíveis mecanismos por trás da diversificação de espécies e da morfologia que poderiam também ser contemplados para outros grupos de organismos. Portanto, a presente tese contribui não só para entendermos os mecanismos que geram e mantém a diversidade de serpentes, mas também para enriquecer a discussão dos mecanismos que geram e mantém a biodiversidade como um todo

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Phylogeographic analyses of the fauna of the Australian wet tropics rainforest have provided strong evidence for long-term isolation of populations among allopatric refugia, yet typically there is no corresponding divergence in morphology. This system provides an opportunity to examine the consequences of geographic isolation, independent of morphological divergence, and thus to assess the broader significance of historical subdivisions revealed through mitochondrial DNA phylogeography. We have located and characterized a zone of secondary contact between two long isolated (mtDNA divergence > 15%) lineages of the skink Carlia rubrigularis using one mitochondrial and eight nuclear (two intron, six microsatellite) markers. This revealed a remarkably narrow (width < 3 km) hybrid zone with substantial linkage disequilibrium and strong deficits of heterozygotes at two of three nuclear loci with diagnostic alleles. Cline centers were coincident across loci. Using a novel form of likelihood analysis, we were unable to distinguish between sigmoidal and stepped cline shapes except at one nuclear locus for which the latter was inferred. Given estimated dispersal rates of 90-133 m x gen(-1/2) and assuming equilibrium, the observed cline widths suggest effective selection against heterozygotes of at least 22-49% and possibly as high as 70%. These observations reveal substantial postmating isolation, although the absence of consistent deviations from Hardy-Weinberg equilibrium at diagnostic loci suggests that there is little accompanying premating isolation. The tight geographic correspondence between transitions in mtDNA and those for nuclear genes and corresponding evidence for selection against hybrids indicates that these morphologically cryptic phylogroups could be considered as incipient species. Nonetheless, we caution against the use of mtDNA phylogeography as a sole criterion for defining species boundaries.

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The molecular clock does not tick at a uniform rate in all taxa but maybe influenced by species characteristics. Eusocial species (those with reproductive division of labor) have been predicted to have faster rates of molecular evolution than their nonsocial relatives because of greatly reduced effective population size; if most individuals in a population are nonreproductive and only one or few queens produce all the offspring, then eusocial animals could have much lower effective population sizes than their solitary relatives, which should increase the rate of substitution of nearly neutral mutations. An earlier study reported faster rates in eusocial honeybees and vespid wasps but failed to correct for phylogenetic nonindependence or to distinguish between potential causes of rate variation. Because sociality has evolved independently in many different lineages, it is possible to conduct a more wide-ranging study to test the generality of the relationship. We have conducted a comparative analysis of 25 phylogenetically independent pairs of social lineages and their nonsocial relatives, including bees, wasps, ants, termites, shrimps, and mole rats, using a range of available DNA sequences (mitochondrial and nuclear DNA coding for proteins and RNAs, and nontranslated sequences). By including a wide range of social taxa, we were able to test whether there is a general influence of sociality on rates of molecular evolution and to test specific predictions of the hypothesis: (1) that social species have faster rates because they have reduced effective population sizes; (2) that mitochondrial genes would show a greater effect of sociality than nuclear genes; and (3) that rates of molecular evolution should be correlated with the degree of sociality. We find no consistent pattern in rates of molecular evolution between social and nonsocial lineages and no evidence that mitochondrial genes show faster rates in social taxa. However, we show that the most highly eusocial Hymenoptera do have faster rates than their nonsocial relatives. We also find that social parasites (that utilize the workers from related species to produce their own offspring) have faster rates than their social relatives, which is consistent with an effect of lower effective population size on rate of molecular evolution. Our results illustrate the importance of allowing for phylogenetic nonindependence when conducting investigations of determinants of variation in rate of molecular evolution.

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Previous studies in our laboratory have shown association of nuclear receptor expression and histological breast cancer grade. To further investigate these findings, it was the objective of this study to determine if expression levels of the estrogen alpha, estrogen beta and androgen nuclear receptor genes varied in different breast cancer grades. RNA extracted from paraffin embedded archival breast tumour tissue was converted into cDNA and cDNA underwent PCR to enable quantitation of mRNA expression. Expression data was normalised against the 18S ribosomal gene multiplex and analysed using ANOVA. Analysis indicated a significant alteration of expression for the androgen receptor in different cancer grades (P=0.014), as well as in tissues that no longer possess estrogen receptor alpha proteins (P=0.025). However, expression of estrogen receptors alpha and beta did not vary significantly with cancer grade (P=0.057 and 0.622, respectively). Also, the expression of estrogen receptor alpha or beta did not change, regardless of the presence of estrogen receptor alpha protein in the tissue (P=0.794 and 0.716, respectively). Post-hoc tests indicate that the expression of the androgen receptor is increased in estrogen receptor negative tissue as well as in grade 2 and grade 3 tumours, compared to control tissue. This increased expression in late stage breast tumours may have implications to the treatment of breast tumours, particularly those lacking expression of other nuclear receptor genes.

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BACKGROUND: Previous studies in our laboratory have shown associations of specific nuclear receptor gene variants with sporadic breast cancer. In order to investigate these findings further, we conducted the present study to determine whether expression levels of the progesterone and glucocorticoid nuclear receptor genes vary in different breast cancer grades. METHODS: RNA was extracted from paraffin-embedded archival breast tumour tissue and converted into cDNA. Sample cDNA underwent PCR using labelled primers to enable quantitation of mRNA expression. Expression data were normalized against the 18S ribosomal gene multiplex and analyzed using analysis of variance. RESULTS: Analysis of variance indicated a variable level of expression of both genes with regard to breast cancer grade (P = 0.00033 for glucocorticoid receptor and P = 0.023 for progesterone receptor). CONCLUSION: Statistical analysis indicated that expression of the progesterone nuclear receptor is elevated in late grade breast cancer tissue.

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Phylogenetic relationships among 37 living species of order Carnivora spanning a relatively broad range of divergence times and taxonomic levels were examined using nuclear sequence data from exon1 of the IRBP gene (approximate to1.3 kb) and first intron

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The taxomic classification and phylogenetic relationships within the bear family remain argumentative subjects in recent years. Prior investigation has been concentrated on the application of different mitochondrial (mt) sequence data, herein we employ tw

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The pantherine lineage of the cat family Felidae (order: Carnivora) includes five big cats of genus Panthera and a great many midsized cats known worldwide. Presumably because of their recent and rapid radiation, the evolutionary relationship among pantherines remains ambiguous. We provide an independent assessment of the evolutionary history of pantherine lineage using two complete mitochondrial (mt) genes (ND2 and ND4) and the nuclear beta-fibrmogen intron 7 gene, whose utility in carnivoran phylogeny was first explored. The available four mt (ND5, cytb, 12S, and 16SrRNA) and two nuclear (IRBP and TTR) sequence loci were also combined to reconstruct phylogeny of 14 closely related cat species. Our analyses of combined mt data (six genes; approximate to 3750 bp) and combined mt and nuclear data (nine genes; approximate to 6500 bp) obtained identical tree topologies, which were well-resolved and strongly supported for almost all nodes. Monophyly of Panthera genus in pantherine lineage was confirmed and interspecific affinities within this genus revealed a novel branching pattern, with P. tigris diverging first in Panthera genus, followed by P. onca, P. leo, and last two sister species P. pardus and P. uncia. In addition, close association of Neofelis nebulosa to Panthera, the phylogenetic redefinition of Otocolobus manil within the domestic cat group, and the relatedness of Acinonyx jubatus and Puma concolor were all important findings in the resulting phylogenies. The potential utilities of nine different genes for phylogenetic resolution of closely related pantherine species were also evaluated, with special interest in that of the novel nuclear beta-fibrinogen intron 7. (c) 2005 Elsevier Inc. All rights reserved.

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The phylogenetic relationships among 12 genera of treefrogs (Family, Rhacophoridae), were investigated based on a large sequence data set, including five nuclear (brain-derived neurotrophic factor, proopiomelanocortin, recombination activating gene 1, tyr