Search

[Traduit par la Redaction] Introduction Allopolyploidization is an evolutionary process involved in plant speciation which occurs naturally by combining two or more different genomes into a single nucleus by inter-specific [...], Recent studies in the genera Aegilops and Triticum showed that allopolyploid formation triggers rapid genetic and epigenetic changes that lead to cytological and genetic diploidization. To better understand the consequences of cytological diploidization, chromosome pairing and seed fertility were studied in [S.sub.1], [S.sub.2], and [S.sub.3] generations of 18 newly formed allopolyploids at different ploidy levels. Results showed that bivalent pairing at first meiotic metaphase was enhanced and seed fertility was improved during each successive generation. A positive linear relationship was found between increased bivalent pairing, improved fertility, and elimination of low-copy noncoding DNA sequences. These findings support the conclusion that rapid elimination of low-copy noncoding DNA sequences from one genome of a newly formed allopolyploid, different sequences from different genomes, is an efficient way to quickly augment the divergence between homoeologous chromosomes and thus bring about cytological diploidization. This facilitates the rapid establishment of the raw allopolyploids as successful, competitive species in nature. Key words: Aegilops, allopolyploidy, bivalent pairing, chromosome-specific sequences, diploidization, Triticum, wheat. De recents travaux au sein des genres Aegilops et Triticum ont montre que la formation d'allopolyploides enclenche de rapides changements epigenetiques qui menent a une diploidisation cytologique et genetique. Afin de mieux comprendre les consequences de la diploidisation cytologique, l'appariement des chromosomes et la fecondite ont ete examines chez les generations [S.sub.1], [S.sub.2] et [S.sub.3] de 18 allopolyploides nouvellement formes et presentant des niveaux de ploidie differents. Les resultats montrent que la formation de bivalents lors de la premiere metaphase meiotique etait superieure et que la fecondite etait accrue avec chaque generation successive. Une relation lineaire positive a ete trouvee entre une formation accrue de bivalents, une fecondite amelioree et l'elimination de sequences d'ADN non-codant a faible nombre de copies. Ces observations supportent la conclusion qu'une elimination rapide des sequences d'ADN non-codant a faible nombre de copies d'un des genomes, possiblement differentes au sein de differents genomes, est un moyen efficace pour augmenter rapidement la divergence nucleotidique entre chromosomes homeologues et entrainer une diploidisation cytologique. Ceci facilite l'etablissement rapide des allopolyploides a l'etat brut en tant qu'especes competitives en nature. Mots-cles : Aegilops, allopolyploidie, formation de bivalents, sequences specifiques des chromosomes, diploidisation, Triticum, ble.

Paleogenomics seeks to reconstruct ancestral genomes from the genes of today's species. The characterization of paleo-duplications represented by 11,737 orthologs and 4,382 paralogs identified in five species belonging to three of the agronomically most important subfamilies of grasses, that is, Ehrhartoideae (rice) Panicoideae (sorghum, maize), and Pooideae (wheat, barley), permitted us to propose a model for an ancestral genome with a minimal size of 33.6 Mb structured in five proto-chromosomes containing at least 9,138 predicted proto-genes. It appears that only four major evolutionary shuffling events ([alpha], [beta], [gamma] and [delta]) explain the divergence of these five cereal genomes during their evolution from a common paleo-ancestor. Comparative analysis of ancestral gene function with rice as a reference indicated that five categories of genes were preferentially modified during evolution. Furthermore, alignments between the five grass proto-chromosomes and the recently identified seven eudicot proto-chromosomes indicated that additional very active episodes of genome rearrangements and gene mobility occurred during angiosperm evolution. If one compares the pace of primate evolution of 90 million years (233 species) to 60 million years of the Poaceae (10,000 species), change in chromosome structure through speciation has accelerated significantly in plants. grasses | paleogenomics

In budding yeast the conserved protein kinase Ipl1 regulates microtubule binding to kinetochores. Chromosome segregation is based on kinetochores, structures that mediate chromosome attachment to the mitotic spindle. Mutants in IPL1, which encodes a protein kinase, have been isolated in a screen for budding yeast mutants with defects in sister chromatid segregation and separation.

The kinesin-like protein CENP-E, binds to kinetochores, and may be important in normal chromosome motility during mitosis. Affinity-purified antibodies were microinjected, blocking the assembly of CENP-E onto kinetochores, to test the in vivo function of CENP-E. Chromosomes lacking CENP-E at their kinetochores located near a pole remained mono-oriented, but those within the spindle made bipolar connections, although they were defective.

Accurate chromosome segregation requires the assembly of only one kinetochore per chromosome in budding yeast. The structure of a four-protein complex, CBF3, that binds to the CDEIII region of Saccharomyces cerevisiae centromeres is reported, using DNA-protein crosslinking and nondenaturing gel analysis. Three subunits of CBF3 were found to be in direct contact with CDEIII, making significant contributes to the energy of CBF3-DNA interaction.

The majority of early-onset familial Alzheimer's disease are due to mutations in two related genes, presenilin 1 and 2. Their function is unknown, although their structural features suggested that they could be membrane proteins. The presenilins were localized, and their colocalization with kinetochores on the nucleoplasmic surface of the inner nuclear membrane, indicate that they could have a role in chromosome organization and segregation.

The sequence of K-12 chromosome in Escherichia coli, which includes a 19-gene cluster responsible for the production of colanic acid, has been determined. The cluster includes genes for GDP-L-fucose synthesis and for the enzyme, GDP-D-mannose 4,6-dehydratase involved in this pathway. The first three genes encode a phosphatase, an outer and an inner membrane lipoprotein, and have homologs in other extracellular polysaccharide gene clusters. These help in the transport of polysaccharide from the cell.

The tfdA gene of the gram negative bacterium Burkholderia sp. strain TFD6 is 99.5% similar to that of the RASC strain. This indicates that the gene is transmitted to other microbes in the environment, as the strains are geographically separated. The tfdA gene is located on a mobile element on the chromosome rather than on a conjugative plasmid. The gene product initiates 2,4-dichlorophenoxyacetic acid degradation which involves activity of alpha-ketoglutarate dioxygenase. The low G+C content of the gene indicates the incorporation of foreign DNA.

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 Brasicca nigra, Brassicaceae. Plants were submitted to beat 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 beat-treated individuals. No effects of beat 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 [F.sub.1] generation. In addition, we propose a DNA damage-repair hypothesis to explain the reduction in rDNA caused by heat shock.

Substitution in the chromosomes of rice and maize is affected by the amino acids present on the sides of the noncoding regions. When the 3' and 5' flanking amino acids are G or C, transversion (Tv) accounts for 25% of the substitutions. However, when both these amino acids are a A or T, 57% of the substitutions are Tv. This effect of the amino acids is probably due to changes in the information reading or the repairing of defects during replication of the chromosome. Substitution is not a common phenomenon in these grasses as the difference in the chromosomes is less than 10%.

Beta-carbolines such as methyl beta-carboline-3-carboxylate (beta-CCM) are inverse agonists that induce seizures and connect to the benzodiazepine receptors in the brain which inhibit the central nervous system. Beta-CCM increases intelligence at low doses, is an anxiogenic at middle doses and becomes a convulsant at high doses. Observations of the circulation of beta-CCM-induced seizures shows that genes on chromosomes 4 and 13 are active in the regulation beta-CCM-induced seizures.

The mutations in the proteolytic enzyme calpain 3 cause limb-girdle muscular dystrophies (LGMDs). The LGMD is an enzyme-regulated inherited disease. The gene which encodes muscle-specific calcium-activated neutral protease 3 (CANP3) is present in the region of 15q15.1-q21.1. The CANP3 is an active gene and regulates the signal transduction. Mutation in CANP3 stops the proteolytic activity and regulatory role of signal transduction. These results indicate an etiology for LGMD diseases.

A morphological study of the inner ear of heterozygous mice shows asymmetric variations of the horizontal canal and a flattening of the crista ampullaris. This is evident from a dominant mutation that developed in transgenic mice due to insertional mutation in heterozygous mice which have a unique facial appearance. Transgene insertion does not affect the role of the closely knitted ataxia locus, and provides a molecular link to genes at the Twirler area of mouse chromosome 18.

The mutation in the MSX2 homeobox gene causes craniosynostosis, a premature fusion of calvarial sutures which results in an aberrant skull shape. The cause of this malady, the human MSX2 gene, localizes to chromosome 5 while the mouse MSX2 gene localizes to calvarial sutures. The mutation is a substitution to a proline, and occurs in an invariant sie with MSX homeodomains.

The distribution of macroH2A (mH2A) in mouse liver nuclei was examined by immunofluorescence, using non-histone antibodies of the mH2A subtypes, mH2A1.2. speckled staining was seen through most of the nuclei in both males and females, although the nuclei of females had large and distinct mH2A-dense regions, named macrochromatin bodies (MCBs). MCBs were detected using tissue fixation and polyclonal antibodies.

Yeast meiotic chromosome core development into full-length synaptonemal complexes must have the MED1 gene product which is a protein kinase homolog that is meiosis-specific. Fluorescent in situ hybridization analysis gives results that show that it is likely that Mek1-mediated phosphorylation of the Red1 protein is needed for meitoic sister-chromatid cohesion. Thus there is a possibility that cohesion is regulated by protein phosphorylation.