Mitochondrial gene order is not conserved in arthropods: prostriate and metastriate tick mitochondrial genomes

The entire mitochondrial genome was sequenced in a prostriate tick, Ixodes hexagonus, and a metastriate tick, Rhipicephalus sanguineus. Both genomes encode 22 tRNAs, 13 proteins, and two ribosomal RNAs. Prostriate ticks are basal members of Ixodidae and have the same gene order as Limulus polyphemus. In contrast, in R. sanguineus, a block of genes encoding NADH dehydrogenase subunit 1 (ND1), tRNA(Leu)(UUR), tRNA(Leu)(CUN), 16S rDNA, tRNA(Val), 12S rDNA, the control region, and the tRNA(Ile) and tRNA(Gln) have translocated to a position between the tRNA(Glu) and tRNA(Phe) genes. The tRNA(Cys) gene has translocated between the control region and the tRNA(Met) gene, and the tRNA(Leu)(CUN) gene has translocated between the tRNA(Ser)(UCN) gene and the control region. Furthermore, the control region is duplicated, and both copies undergo concerted evolution. Primers that flank these rearrangements confirm that this gene order is conserved in all metastriate ticks examined. Correspondence analysis of amino acid and codon use in the two ticks and in nine other arthropod mitochondrial genomes indicate a strong bias in R. sanguineus towards amino acids encoded by AT-rich codons.      

Nucleotide polymorphism at the alcohol dehydrogenase locus of pocket gophers, genus Geomys

Using the strictly neutral model as a null hypothesis, we tested for deviations from expected levels of nucleotide polymorphism at the alcohol dehydrogenase locus (Adh-1) within and among four species of pocket gophers (Geomys bursarius major, G. knoxjonesi, G. texensis llanensis, and G. attwateri). The complete protein-encoding region was examined, and 10 unique alleles, representing both electromorphic and cryptic alleles, were used to test hypotheses (e.g., the neutral model) concerning the maintenance of genetic variation. Nineteen variable sites were identified among the 10 alleles examined, including 9 segregating sites occurring in synonymous positions and 10 that were nonsynonymous. Several statistical methods, including those that test for within-species variation as well as those that examine variation within and among species, failed to reject the null hypothesis that variation (both within and between species of Geomys) at the Adh locus is consistent with the neutral theory. However, there was significant heterogeneity in the ratio of polymorphism to divergence across the gene, with polymorphisms clustered in the first half of the coding region and fixed differences clustered in the second half of the gene. Two alternative hypotheses are discussed as possible explanations for this heterogeneity: an old balanced polymorphism in the first half of the gene or a recent selective sweep in the second half of the gene.      

Involvement of intracellular calcium stores in Giardia lamblia induced diarrhoea in mice

Abstract The transmucosal fluxes of Na⁺ and Cl⁻ were studied in Giardia lamblia -infected mice in the presence of absence of dantrolene (1-(5( p -nitrophenyl)furfurilidene-amino) hydantoin sodiumhydrate ). There was net secretion of Na⁺ and Cl⁻ in infected animals, while in control animals there was net absorption of these ions. The addition of dantrolene resulted in significant net increase in absorption of Na⁺ and Cl⁻ in control and experimental groups. Further, mouse intestinal epithelial cells were labelled with [³²P]Pi and then treated with G. lamblia trophozoites and their excretory secretory products separately. The optimum time for inositol triphosphate formation was 15 min in control enterocytes as well as in treated enterocytes. A plateau was formed at higher concentrations. Since raised inositol triphosphate levels mobilize Ca²⁺ from intracellular stores and dantrolene traps Ca²⁺ within intracellular calcium stores, the present study thus suggests that intracellular calcium stores are involved in G. lamblia -induced diarrhoea in mice.     

Vitamin C deficiency in Channa punctatus Bloch

The results of a series of experiments on Channa punctatus previously conditioned to a complete synthetic diet and later fed vitamin C deficient diet for 210 days followed by 30 days of recovery with fortified vitamin C ration are reported. The survival, growth, morphological abnormalities and biochemical changes in tissue ascorbic acid and cholesterol levels were studied.
Deficiency of vitamin C resulted in a mortality of up to 25% and retarded growth accompanied by anorexia and loss of weight. Marked skeletal abnormalities, viz. , lordosis, scoliosis and degenerative changes in the thoracic vertebrae were revealed by X-ray studies. Biochemical investigations showed a significant decrease in blood and kidney ascorbic acid levels within a month of feeding the deficient diet. A prolonged deficiency beyond 150 days resulted in a rapid rise in the cholesterol content of the liver. These biochemical changes were reversed when vitamin C was added to the ration.     

Thyroid hormone dysregulation in intrauterine growth retardation associated with maternal malnutrition and/or anemia.

Data on the effect of maternal malnutrition and/or anemia on thyroid hormone regulation in human fetuses are scarce, and would be of great importance in examining the relevance of Barker's hypothesis, which proposes adaptation of fetuses to undernutrition leading to permanent metabolic and endocrine changes that form the basis of adult diseases. To examine the quantitative variations in thyroid hormone profile of neonates born to malnourished and/or anemic mothers, we quantitated the T3, T4, rT3 and TSH levels in cord blood of neonates and maternal blood of their corresponding mothers that are malnourished and/or anemic. Further, we classified neonates born to each of these groups of mothers into Small for Gestational Age (SGA) or Appropriate for Gestational Age (AGA) based on the intrauterine growth curve for our population, and examined the thyroid hormone profile in these neonates. Our results show that firstly, the effects of malnutrition or anemia on thyroid hormone profile are distinct, secondly, significantly higher levels of cord blood T4 and correspondingly lower levels of T3 and rT3 are observed in the neonates born to anemic and malnourished mothers and thirdly, decreases in cord blood T3 levels were observed in Small for Gestational Age neonates born to anemic mothers. These observations lead us to speculate that alterations in the pituitary-thyroid function result in beneficial adaptations to the hostile intrauterine environment in malnutrition related growth retardation and anemia.     

Clines, clusters, and the effect of study design on the inference of human population structure

Previously, we observed that without using prior information about individual sampling locations, a clustering algorithm applied to multilocus genotypes from worldwide human populations produced genetic clusters largely coincident with major geographic regions. It has been argued, however, that the degree of clustering is diminished by use of samples with greater uniformity in geographic distribution, and that the clusters we identified were a consequence of uneven sampling along genetic clines. Expanding our earlier dataset from 377 to 993 markers, we systematically examine the influence of several study design variables—sample size, number of loci, number of clusters, assumptions about correlations in allele frequencies across populations, and the geographic dispersion of the sample—on the “clusteredness” of individuals. With all other variables held constant, geographic dispersion is seen to have comparatively little effect on the degree of clustering. Examination of the relationship between genetic and geographic distance supports a view in which the clusters arise not as an artifact of the sampling scheme, but from small discontinuous jumps in genetic distance for most population pairs on opposite sides of geographic barriers, in comparison with genetic distance for pairs on the same side. Thus, analysis of the 993-locus dataset corroborates our earlier results: if enough markers are used with a sufficiently large worldwide sample, individuals can be partitioned into genetic clusters that match major geographic subdivisions of the globe, with some individuals from intermediate geographic locations having mixed membership in the clusters that correspond to neighboring regions.     

The proteolytic stability of 'designed' beta-peptides containing alpha-peptide-bond mimics and of mixed alpha,beta-peptides: application to the construction of MHC-binding peptides

Whereas alpha-peptides are rapidly degraded in vivo and in vitro by a multitude of peptidases, substrates constructed entirely of or incorporating homologated alpha-amino acid (i.e., beta-amino acid) units exhibit a superior stability profile. Efforts made so far to proteolytically hydrolyze a beta-beta peptide bond have not proved fruitful; a study aimed at breaching this proteolytic stability is discussed here. A series of such bonds have been designed with side-chain groups similar in relative positions (constitution) and three-dimensional arrangements (configuration) as found about alpha-peptidic amide bonds. Increasing the prospect for degradation would permit the tuning of beta-peptide stability; here, however, no cleavage was observed (1, 2, 4-6, Table 1). Peptides comprised of alpha- and beta-amino acids (mixed alpha,beta-peptides, 8-11) are expected to benefit from both recognition by a natural receptor and a high level of proteolytic stability, ideal characteristics of pharmacologically active compounds. Beta3-peptides containing alpha-amino acid moieties at the N-terminus are degraded, albeit slowly, by several peptidases. Of particular interest is the ability of pronase to cleave an alpha-beta peptide bond, namely that of alphaAla-beta3 hAla. Significantly, successful hydrolysis is independent of the configuration of the beta-amino acid. Some of the alpha,beta-peptides discussed here are being investigated for their binding affinities to class I MHC proteins. The computer-programming steps required to prepare alpha,beta-peptides on an automated peptide synthesizer are presented.     

All-trans-retinal is a closed-state inhibitor of rod cyclic nucleotide-gated ion channels

Rod vision begins when 11-cis-retinal absorbs a photon and isomerizes to all-trans-retinal (ATR) within the photopigment, rhodopsin. Photoactivated rhodopsin triggers an enzyme cascade that lowers the concentration of cGMP, thereby closing cyclic nucleotide-gated (CNG) ion channels. After isomerization, ATR dissociates from rhodopsin, and after a bright light, this release is expected to produce a large surge of ATR near the CNG channels. Using excised patches from Xenopus oocytes, we recently showed that ATR shuts down cloned rod CNG channels, and that this inhibition occurs in the nanomolar range (aqueous concentration) at near-physiological concentrations of cGMP. Here we further characterize the ATR effect and present mechanistic information. ATR was found to decrease the apparent cGMP affinity, as well as the maximum current at saturating cGMP. When ATR was applied to outside-out patches, inhibition was much slower and less effective than when it was applied to inside-out patches, suggesting that ATR requires access to the intracellular surface of the channel or membrane. The apparent ATR affinity and maximal inhibition of heteromeric (CNGA1/CNGB1) channels was similar to that of homomeric (CNGA1) channels. Single-channel and multichannel data suggest that channel inhibition by ATR is reversible. Inhibition by ATR was not voltage dependent, and the form of its dose-response relation suggested multiple ATR molecules interacting per channel. Modeling of the data obtained with cAMP and cGMP suggests that ATR acts by interfering with the allosteric opening transition of the channel and that it prefers closed, unliganded channels. It remains to be determined whether ATR acts directly on the channel protein or instead alters channel-bilayer interactions.     

Synthesis and biological activity of novel antibacterial quinazolines

Novel quinazolines, having interesting antibacterial activity have been prepared, characterized and tested against a panel of susceptible and resistant Gram positive and Gram negative organisms.