Frequent mitochondrial gene introgression among high elevation Tibetan megophryid frogs revealed by conflicting gene genealogies

Historical mitochondrial introgression causes differences between a species' mitochondrial gene genealogy and its nuclear gene genealogy, making tree-based species delineation ambiguous. Using sequence data from one mitochondrial gene (cytochrome b ) and three nuclear genes (introns), we examined the evolutionary history of four high elevation Tibetan megophryid frog species, Scutiger boulengeri , Scutiger glandulatus , Scutiger mammatus and Scutiger tuberculatus . The three nuclear genes shared a similar history but the mitochondrial gene tree suggested a drastically different evolutionary scenario. The conflicts between them were explained by multiple episodes of mitochondrial introgression events via historical interspecific hybridization. 'Foreign' mitochondrial genomes might have been fixed in populations and extended through a large portion of the species' distribution. Some hybridization events were probably as old as 10 Myr, while others were recent. An F₁ hybrid was also identified. Historical hybridization events among the four species appeared to be persistent and were not restricted to the period of Pleistocene glaciation, as in several other well-studied cases. Furthermore, hybridization involved several species and occurred in multiple directions, and there was no indication of one mitochondrial genome being superior to others. In addition, incomplete lineage sorting resulting from budding speciation may have also explained some discrepancies between the mitochondrial DNA and nuclear gene trees. Combining all evidences, the former ' Scutiger mammatus ' appeared to be two species, including a new species. With the availability of a wide range of highly variable nuclear gene markers, we recommend using a combination of mitochondrial gene and multiple nuclear genes to reveal a complete species history.     

RBM15结合促进RNA内含子或外显子滞留

RBM15是一种RNA结合蛋白,参与到RNA的m6A修饰及可变剪接调控中.然而,RBM15在转录组水平如何调控可变剪接尚不清楚.本研究应用超分辨率荧光显微镜技术发现,RBM15在细胞核中形成斑点状结构,且与核斑有密切接触或完全定位于核斑中.核斑为细胞核中无膜细胞器,富含多种剪接因子,这提示RBM15可能参与到可变剪接的调控过程中.为了确定RBM15能否及如何调控可变剪接,我们利用siRNA敲低RBM15,并对敲低RBM15和野生型细胞进行二代测序.结果显示,敲低RBM15能够引起1 111个转录本中的1 279个可变剪接事件的变化.与已发表的RBM15-CLIP数据进行比较分析,我们发现,这1 111个转录本中,有191个能够与RBM15结合,提示这191个转录本可能为RBM15调控的直接靶标.进一步的分析表明,RBM15结合能够促进这191个转录本中的121个发生内含子或外显子的滞留.该研究揭示了RBM15在转录组水平调控可变剪接的规律.     

HLA class I-related impairment in IL-2 production and lymphocyte response to microbial antigens in reactive arthritis

The contribution of certain Gram-negative bacteria and host HLA class I Ag to the development of reactive arthritis (ReA)3 has strong epidemiologic support but the pathogenesis of the arthritis is unknown. An outbreak of Salmonella typhimurium afforded the opportunity to compare the immune response to the organism between those who developed ReA (ReA+, n = 11) with those who did not (ReA-, n = 12). Of the 11 ReA+ patients, 4 were B27-positive and 6 were B7-positive; of the ReA- patients none was B27- or B7-positive. The causative pathogen S. typhimurium phage 22 was used to examine PBL proliferation by [3H]thymidine incorporation. Impairment in lymphocyte response to S. typhimurium in ReA+ compared with ReA- was demonstrated by: i) lower stimulation index (1.9 +/- 0.3 for ReA+, 5.7 +/- 0.6 for ReA-, p less than 0.01); ii) lower in vitro Ig production; and iii) lower Ag-induced IL-2 production. Mixing experiments did not demonstrate a soluble suppressor factor in ReA+ supernatants. Thus, after infection with S. typhimurium there is an impairment in cellular immunity that has correlates in immunogenetic and clinical features of the infected population.     

Antibacterial Screening of Secreted Compounds Produced by the Phase I Variant of Photorhabdus luminescens

In this study, antibacterial activity of metabolites secreted by the phase I variant of Photorhabdus luminescens was investigated. Bioactivity of these metabolites was screened against 28 different bacterial species and strains. Bacterial sensitivity was determined by a modified-version of the Kirby–Bauer disk diffusion susceptibility method, whereas the phase I variant’s culture permeate was utilized as the “antibacterial” agent. This investigation demonstrates that 11 of the 28 bacterial species tested were sensitive to at least one of the secreted compounds or a combination thereof.     

COMPARATIVE STUDIES ON RESPIRATION : XX. THE CAUSE OF PARTIAL RECOVERY.

The respiration of Chlorella is diminished by exposure to hypertonic salt solutions. After a short exposure there is complete recovery when the algæ are removed to the normal medium. After a longer exposure recovery may be incomplete, as shown by the fact that the rate of respiration fails to rise to the normal level. Staining with methylene blue indicates that few, if any, of the cells are killed as the result of the exposure. It would therefore seem that the treatment produces a persistent lowering of the rate of metabolism. Such a condition of metabolism is also found after exposure to chloroform.     

Methodology for the study of the effect of drugs on development and DNA replication in Drosophila melanogaster embryonic tissue

Methodology is described that will permit the study of the effect of various drugs on development and DNA replication in the cleavage nuclei of Drosophila eggs. It is shown that permeabilized eggs can be exposed to an aqueous incubation medium for up to 30 min without measureable effects on development and that such incubations can be performed with eggs that have a relatively sharp age distribution. The effect on development and viability of a variety of drugs has been examined as an aid for future studies directed toward achieving synchronous development in a population of eggs and electron microscopic studies of DNA replication in the presence of various drugs.     

Mechanical loading attenuates bone loss due to immobilization and calcium deficiency.

Our purpose was to determine the effects of a mechanical loading intervention on mass, geometry, and strength of rat cortical bone during a period of disuse concurrent with calcium deficiency (CD). Adult female rats were assigned to unilateral hindlimb immobilization, immobilized-loaded, or control (standard chow, 1.85% calcium) treatments. Both immobilized groups were fed a CD rat chow (0.01% calcium) to induce high bone turnover. Three times weekly, immobilized-loaded rats were subjected to 36 cycles of 4-point bending of the immobilized lower leg. After 6 wk, the immobilized rats exhibited decreased tibial shaft bone mineral density (-12%), ultimate load (-19%), and stiffness (-20%; tested in 3-point bending to failure) vs. control rats. Loading prevented this decline in bone density and attenuated decreases in ultimate load and stiffness. Elastic modulus was unaffected by disuse or loading. Bone cross-sectional area in the immobilized-loaded rats was equivalent to that of control animals, even though endocortical resorption continued unabated. On the medial periosteum, percent mineralizing surface doubled vs. that in immobilized rats. This loading regimen stimulated periosteal mineralization and maintained bone mineral density, thereby attenuating the loss in bone strength incurred with disuse and concurrent calcium deficiency.