26 research outputs found
Fine-Scale Phylogeographic Structure of Borrelia lusitaniae Revealed by Multilocus Sequence Typing
Borrelia lusitaniae is an Old World species of the Lyme borreliosis (LB) group of tick-borne spirochetes and prevails mainly in countries around the Mediterranean Basin. Lizards of the family Lacertidae have been identified as reservoir hosts of B. lusitaniae. These reptiles are highly structured geographically, indicating limited migration. In order to examine whether host geographic structure shapes the evolution and epidemiology of B. lusitaniae, we analyzed the phylogeographic population structure of this tick-borne bacterium using a recently developed multilocus sequence typing (MLST) scheme based on chromosomal housekeeping genes. A total of 2,099 questing nymphal and adult Ixodes ricinus ticks were collected in two climatically different regions of Portugal, being ∼130 km apart. All ticks were screened for spirochetes by direct PCR. Attempts to isolate strains yielded 16 cultures of B. lusitaniae in total. Uncontaminated cultures as well as infected ticks were included in this study. The results using MLST show that the regional B. lusitaniae populations constitute genetically distinct populations. In contrast, no clear phylogeographic signals were detected in sequences of the commonly used molecular markers ospA and ospC. The pronounced population structure of B. lusitaniae over a short geographic distance as captured by MLST of the housekeeping genes suggests that the migration rates of B. lusitaniae are rather low, most likely because the distribution of mediterranean lizard populations is highly parapatric. The study underlines the importance of vertebrate hosts in the geographic spread of tick-borne microparasites
Structural Characteristics and Stellar Composition of Low Surface Brightness Disk Galaxies
We present UBVI surface photometry of a sample of low surface brightness
(LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential
disks with no preferred value for either scale length, central surface
brightness, or rotational velocity. Indeed, the distribution of scale lengths
is indistinguishable from that of high surface brightness spirals, indicating
that dynamically similar galaxies (e.g., those with comparable Rv^2) exist over
a large range in surface density.
These LSB galaxies are strikingly blue. The complete lack of correlation
between central surface brightness and color rules out any fading scenario.
Similarly, the oxygen abundances inferred from HII region spectra are
uncorrelated with color so the low metallicities are not the primary cause of
the blue colors. While these are difficult to interpret in the absence of
significant star formation, the most plausible scenario is a stellar population
with a young mean age stemming from late formation and subsequent slow
evolution.
These properties suggest that LSB disks formed from low initial overdensities
with correspondingly late collapse times.Comment: Astronomical Journal, in press 45 pages uuencoded postscript (368K)
including 9 multipart figures also available by anonymous ftp @
ftp.ast.cam.ac.uk /pub/ssm/phot.uu CAP-30-210442962983742937
Claudins in renal physiology and disease
The tight junction forms the paracellular permeability barrier in all epithelia, including the renal tubule. Claudins are a family of tight junction membrane proteins with four transmembrane domains that form the paracellular pore and barrier. Their first extracellular domain appears to be important for determining selectivity. A number of claudin isoforms have been found to be important in renal tubule function, both in adults and in neonates. Familial hypomagnesemic hypercalciuria with nephrocalcinosis is an autosomal recessive syndrome characterized by impaired reabsorption of Mg and Ca in the thick ascending limb of Henle's loop. Mutations in claudin-16 and 19 can both cause this syndrome, but the pathophysiological mechanism remains controversial