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At least 289 records · Page 16Linked to original sources
PubMed2004

Molecular systematics and time-scale for the evolution of Timarcha, a leaf-beetle genus with a disjunct Holarctic distribution.

In recent years we have investigated the evolution of the Holarctic leaf-beetle genus Timarcha using molecular approaches, but to date several important questions remained unanswered, including its systematic arrangement in a temporal context, or the phylogenetic placement of the Nearctic taxa. Here I present a reanalysis of available genetic data together with newly generated data for key taxa (markers 16S rDNA, CO2, ITS-2, and 18S rDNA), including the Nearctic species (subgenus Americanotimarcha), using direct optimization-based phylogenetic reconstructions. Lineage ages are estimated using maximum likelihood branch-length estimates and the molecular clock calibration derived from several presumed vicariance events in the Mediterranean. Phylogenetic analyses and 18S rDNA divergences suggest the ancient divergence of the Nearctic and Palaearctic lineages, related to the North Atlantic opening in the middle Eocene. The diversification of the Palaearctic Timarcha seems closely related to the geological evolution of the Mediterranean area during the Tertiary, with Pleistocenic climate changes affecting species ranges and lineage extinction, but not resulting in extensive speciation.

Animals↗
PubMed2003

The Caenorhabditis elegans SCC-3 homologue is required for meiotic synapsis and for proper chromosome disjunction in mitosis and meiosis.

The product of the Caenorhabditis elegans ORF F18E2.3 is homologous to the cohesin component Scc3p. By antibody staining the product of F18E2.3 is found in interphase and early meiotic nuclei. At pachytene it localizes to the axes of meiotic chromosomes but is no longer detectable on chromatin later in meiosis or in mitoses. Depletion of the gene product by RNAi results in aberrant mitoses and meioses. In meiosis, homologous pairing is defective during early meiotic prophase and at diakinesis there occur univalents consisting of loosely connected sister chromatids or completely separated sisters. The recombination protein RAD-51 accumulates in nuclear foci at higher numbers during meiotic prophase and disappears later than in wild-type worms, suggesting a defect in the repair of meiotic double-stranded DNA breaks. Embryos showing nuclei of variable size and anaphase bridges, indicative of mitotic segregation defects, are frequently observed. In the most severely affected gonads, nuclear morphology cannot be related to any specific stage. The cytological localization and the consequences of the lack of the protein indicate that C. elegans SCC-3 is essential for sister chromatid cohesion both in mitosis and in meiosis.

Animals↗
PubMed1991

Altering the angulation of a curved osteotome--does it have effects on the type of pterygomaxillary disjunction in Le Fort I osteotomy? An experimental study.

A standard Le Fort I osteotomy was performed on 12 cadavers to determine whether the incidence of pterygoid plate fractures could be reduced by increasing the angle of the curved osteotome relative to the sagittal plane. In the group where an osteotome with the usual angulation was employed, fractures occurred on 9 of 12 sides. In the increased angulation group, 5 of 12 pterygoid plates were fractured. All fractures were restricted to the level of the horizontal osteotomy cut. It is concluded that increased angulation of a curved osteotome can decrease the incidence of fractures of the pterygoid plates. This procedure, however, is not recommended because it can cause fracture of the palatine bone or displacement of the fractured pterygoid plate fragment posteriorly.

Adult↗