Biogeographical analysis of two Polypodium species complexes (Polypodiaceae) in Mexico and Central America

We analyzed the geographical and elevational distributions of two Polypodium complexes from Mexico and Central America. Distribution data of nine species of the Polypodium colpodes complex and the Polypodium plesiosorum complex were obtained from almost 1500 herbarium specimens, field collections in Mexico and Costa Rica, and literature studies. The presence of each species was recorded for each Mesoamerican country, in 1° × 1° grid‐cells and biogeographical provinces. The rarity of species was also evaluated. Although the two complexes show extensive overlap, the P. colpodes complex is distributed mainly along the Pacific versant of Mexico and Central America, whereas the P. plesiosorum complex occurs mainly along the Atlantic versant. Those biogeographical provinces with maximum species diversity are Chiapas (seven species), Sierra Madre del Sur (six species), and the Trans‐Mexican Volcanic belt (six species). Grid‐cells with more species are located mainly in the mountains of central‐southern Mexico and northern Central America. Richness does not decrease or increase with latitude. Elevation distributions showed that most Polypodium species are concentrated in the montane interval and three species groups were recognized based on elevational preferences. Polypodium colpodes and P. plesiosorum are the most widely distributed species, whereas Polypodium castaneum and Polypodium flagellare are the only two species that possess the three attributes of rarity (narrow geographical distribution, high habitat specificity, and scarce local populations). Polypodium species of both complexes are present mainly in the montane regions of the study area and show some degree of geographical sympatry, especially in southern Mexico and northern Central America. This overlapping is explained by the elevation tolerance within montane systems and because most species inhabit three or more vegetation types. The distributional patterns of these complexes coincided with the three regional highlands of Mesoamerica, which are separated from each other by the Isthmus of Tehuantepec and by the lowlands of Nicaragua. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Sensitivity of pathogenic and free-living Leptospira spp. to UV radiation and mitomycin C

The habitats for the two major Leptospira spp. differ. The main habitat of L. biflexa is soil and water, whereas L. interrogans primarily resides in the renal tubules of animals. We investigated whether these two species, along with L. illini (species incertae sedis), differ with respect to their sensitivity to UV radiation. The doses of UV resulting in 37, 10, and 1% survival were determined for representative serovars from each species. L. interrogans serovar pomona was 3.0 to 4.8 times more sensitive to UV than the other Leptospira species under the 37, 10, and 1% survival parameters. In comparison to other bacteria, L. interrogans serovar pomona is among the most sensitive to UV. In a qualitative UV sensitivity assay, L. interrogans serovars were found to be in general more sensitive than L. biflexa serovars. All three species were found to have a photoreactivation DNA repair mechanism. Since organisms that are resistant to UV are often resistant to the DNA cross-linking agent mitomycin C, we tested the relative sensitivity of several Leptospira serovars to this compound. With few exceptions, L. biflexa and L. illini serovars were considerably more resistant to mitomycin C than the L. interrogans serovars. The mitomycin C sensitivity assay could be a useful addition to current characterization tests used to differentiate the Leptospira species.     

Ischemic dysfunction in transgenic mice expressing troponin I lacking protein kinase C phosphorylation sites

To determine the in vivo functional significance of troponin I (TnI) protein kinase C (PKC) phosphorylation sites, we created a transgenic mouse expressing mutant TnI, in which PKC phosphorylation sites at serines-43 and -45 were replaced by alanine. When we used high-perfusate calcium as a PKC activator, developed pressures in transgenic (TG) perfused hearts were similar to wild-type (WT) hearts (P = not significant, NS), though there was a 35% and 32% decrease in peak-systolic intracellular calcium (P < 0.01) and diastolic calcium (P < 0.005), respectively. The calcium transient duration was prolonged in the TG mice also (12-27%, ANOVA, P < 0.01). During global ischemia, TG hearts developed ischemic contracture to a greater extent than WT hearts (41 +/- 18 vs. 69 +/- 10 mmHg, perfusate calcium 3.5 mM, P < 0.01). In conclusion, expression of mutant TnI lacking PKC phosphorylation sites results in a marked alteration in the calcium-pressure relationship, and thus susceptibility to ischemic contracture. The reduced intracellular calcium and prolonged calcium transients suggests that a potent feedback mechanism exists between the myofilament and the processes controlling calcium homeostasis.     

Distribution and conservation of mobile elements in the genus Drosophila

Essentially nothing is known of the origin, mode of transmission, and evolution of mobile elements within the genus Drosophila. To better understand the evolutionary history of these mobile elements, we examined the distribution and conservation of homologues to the P, I, gypsy, copia, and F elements in 34 Drosophila species from three subgenera. Probes specific for each element were prepared from D. melanogaster and hybridized to genomic DNA. Filters were washed under conditions of increasing stringency to estimate the similarity between D. melanogaster sequences and their homologues in other species. The I element homologues show the most limited distribution of all elements tested, being restricted to the melanogaster species group. The P elements are found in many members of the subgenus Sophophora but, with the notable exception of D. nasuta, are not found in the other two subgenera. Copia-, gypsy-, and F-element homologues are widespread in the genus, but their similarity to the D. melanogaster probe differs markedly between species. The distribution of copia and P elements and the conservation of the gypsy and P elements is inconsistent with a model that postulates a single ancient origin for each type of element followed by mating-dependent transmission. The data can be explained by horizontal transmission of mobile elements between reproductively isolated species.      

Role of the reticulum in the stability and shape of the isolated human erythrocyte membrane

In order to examine the widely held hypothesis that the reticulum of proteins which covers the cytoplamsic surface of the human erythrocyte membrane controls cell stability and shape, we have assessed some of its properties. The reticulum, freed of the bilayer by extraction with Triton X-100, was found to be mechanically stable at physiological ionic strength but physically unstable at low ionic strength. The reticulum broke down after a characteristic lag period which decreased 500-fold between 0 degrees and 37 degrees C. The release of polypeptide band 4.1 from the reticulum preceded that of spectrin and actin, suggesting that band 4.1 might stabilize the ensemble but is not essential to its integrity. The time-course of breakdown was similar for ghosts, the reticulum inside of ghosts, and the isolated reticulum. However, at very low ionic strength, the reticulum was less stable within the ghost than when free; at higher ionic strength, the reverse was true. Over a wide range of conditions the membrane broke down to vesicles just as the reticulum disintegrated, presumably because the bilayer was mechanically stabilized by this network. The volume of both ghosts and naked reticula varied inversely and reversibly with ionic strength. The volume of the naked reticulum varied far more widely than the ghost, suggesting that its deformation was normally limited by the less extensible bilayer. The contour of the isolated reticulum was discoid and often dimpled or indented, as visualized in the fluorescence microscope after labeling of the ghosts with fluoroscein isothiocyanate. Reticula derived from ghosts which had lost the ability to crenate in isotonic saline were shriveled, even though the bilayer was smooth and expanded. Conversly, ghosts crenated by dinitrophenol yielded smooth, expanded reticula. We conclude that the reticulum is a durable, flexible, and elastic network which assumes and stabilizes the contour of the membrane but is not responsible for its crenation.     

Refinement of 2q and 7p loci in a large multiplex NTD family

BACKGROUND: NTDs are considered complex disorders that arise from an interaction between genetic and environmental factors. NTD family 8776 is a large multigenerational Caucasian family that provides a unique resource for the genetic analysis of NTDs. Previous linkage analysis using a genome‐wide SNP screen in family 8776 with multipoint nonparametric mapping methods identified maximum LOD* scores of ～3.0 mapping to 2q33.1–q35 and 7p21.1–pter. METHODS: We ascertained an additional nuclear branch of 8776 and conducted additional linkage analysis, fine mapping, and haplotyping. Expression data from lymphoblast cell lines were used to prioritize candidate genes within the minimum candidate intervals. Genomic copy number changes were evaluated using BAC tiling arrays and subtelomeric fluorescent in situ hybridization probes. RESULTS: Increased evidence for linkage was observed with LOD* scores of ～3.3 for both regions. Haplotype analyses narrowed the minimum candidate intervals to a 20.3 Mb region in 2q33.1–q35 between markers rs1050347 and D2S434, and an 8.3 Mb region in 7p21.1–21.3 between a novel marker 7M0547 and rs28177. Within these candidate regions, 16 genes were screened for mutations; however, no obvious causative NTD mutation was identified. Evaluation of chromosomal aberrations using comparative genomic hybridization arrays, subtelomeric fluorescent in situ hybridization, and copy number variant detection techniques within the 2q and 7p regions did not detect any chromosomal abnormalities. CONCLUSIONS: This large NTD family has identified two genomic regions that may harbor NTD susceptibility genes. Ascertainment of another branch of family 8776 and additional fine mapping permitted a 9.1 Mb reduction of the NTD candidate interval on chromosome 7 and 37.3 Mb on chromosome 2 from previously published data. Identification of one or more NTD susceptibility genes in this family could provide insight into genes that may affect other NTD families. Birth Defects Research (Part A), 2008. © 2008 Wiley‐Liss, Inc.