Population Genetic Structure of Neoschoengastia Gallinarum in China Based on Mitochondrial DNA Markers

Background: Neoschoengastia gallinarum is a widespread agricultural pest in China.The larvae of N. gallinarum are parasitic on the body surface of poultry. Performance, carcass quality, and normal marketing of mite infected broilers are severely affected by pruritus and pockmark lesions on the body surface. In China, N. gallinarum research has primarily focused on occurrence regularity, biology, and control methods. The genetic structure, variation, and genetic relationship between the N. gallinarum populations in China are still unclear.Methods: Genetic variations and structure among populations of N. gallinarum was examined and analyzed based on the nucleotide sequences of a 1522 nt variable region of the mitochondrial tandem genes (COI, COII, and ND5) among 4 populations from 7 collection sites in southern China.Results: A total of 192 individuals in 4 populations were analyzed. The tandem genes sequences were aligned, and 75 haplotypes were detected, 4 of these shared between populations. The range of haplotype diversity was from 0.860 (FJ) to 0.978 (GX). The pairwise FST values among populations were higher (0.096-0.551).The haplotype network mediation map and phylogenetic tree showed that the haplotypes were divided into two clade, Which did not completely follow the distribution rule of geographical populations. The AMOVA result showed that the percentage of variation within populations (72.94%) was higher than that among populations (27.06%). Neutral test and mismatch analysisrevealed that N. gallinarum had not experienced an obvious population expansion in recent historical periods, and the population size was relatively stable.Conclusions: The N. gallinarum population showed high genetic diversity based on mitochondrial tandem genes analysis and strong ecological adaptability. Despite the fact that geogrphic isolation causes certain genetic differentiation among populations, N. gallinarum high gene flow among populations as a result of human trade activities, and there was no obvious geographical genetic structure.

Unique features of transcription termination and initiation at closely spaced tandem human genes

The synthesis of RNA Polymerase II (Pol2) products, which include messenger RNAs or long noncoding RNAs, culminates in transcription termination. How the transcriptional termination of a gene impacts the activity of promoters found immediately downstream of it, and which can be subject to potential transcriptional interference, remains largely unknown. We examined in an unbiased manner features of the intergenic region of pairs of tandem and closely spaced (<2kb) genes found on the same strand. Intergenic regions separating tandem genes are enriched with Guanines and are characterized by binding of several proteins, including AGO1 and AGO2 of the RNA interference pathway. Additionally, we found that Pol2 with a specific modification pattern is particularly enriched in this region, and it is lost upon perturbations affecting splicing or transcriptional elongation. Perturbations of genes involved in Pol2 pausing and R loop biology preferentially affect expression of downstream genes in tandem gene pairs. Overall, we find that features associated with potential Pol2 recycling rather than those associated with avoidance of transcriptional interference are the predominant driving force shaping these regions.

A Cluster of Four Surface Antigen Genes Specifically Expressed in Bradyzoites, SAG2CDXY, Plays an Important Role in Toxoplasma gondii Persistence

ABSTRACT Toxoplasma gondii is one of the most successful protozoan parasites of warm-blooded animals. Stage-specific expression of its surface molecules is thought to be key to its ability to establish chronic infection in immunocompetent animals. The rapidly dividing tachyzoite stage displays a different subset of family of surface antigen 1 (SAG1)-related sequences (SRSs) from that displayed by the encysted bradyzoite stage. It is possible that this switch is necessary to protect the bradyzoites against an immune response raised against the tachyzoite stage. Alternatively, it might be that bradyzoite SRSs evolved to facilitate invasion of different cell types, such as those found in the brain, where cysts develop, or the small intestine, where bradyzoites must enter after oral infection. Here we studied the function of a cluster of four tandem genes, encoding bradyzoite SRSs called SAG2C, -D, -X, and -Y. Using bioluminescence imaging of mice infected with parasites expressing firefly luciferase (FLUC) driven by the SAG2D promoter, we show stage conversion for the first time in living animals. A truncated version of the SAG2D promoter (SAG2Dmin) gave efficient expression of FLUC in both tachyzoites and bradyzoites, indicating that the bradyzoite specificity of the complete SAG2D promoter is likely due to an element(s) that normally suppresses expression in tachyzoites. Comparing mice infected with the wild type or a mutant where the SAG2CDXY cluster of genes has been deleted (ΔSAG2CDXY), we demonstrate that whereas ΔSAG2CDXY parasites are less capable of maintaining a chronic infection in the brain, they do not show a defect in oral infectivity.

Novel organization of genes in a phthalate degradation operon of Mycobacterium vanbaalenii PYR-1

Mycobacterium vanbaalenii PYR-1 is capable of degrading polycyclic aromatic hydrocarbons (PAHs) to ring cleavage metabolites. This study identified and characterized a putative phthalate degradation operon in the M. vanbaalenii PYR-1 genome. A putative regulatory protein (phtR) was encoded divergently with five tandem genes: phthalate dioxygenase large subunit (phtAa), small subunit (phtAb), phthalate dihydrodiol dehydrogenase (phtB), phthalate dioxygenase ferredoxin subunit (phtAc) and phthalate dioxygenase ferredoxin reductase (phtAd). A 6·7 kb EcoRI fragment containing these genes was cloned into Escherichia coli and converted phthalate to 3,4-dihydroxyphthalate. Homologues to the operon region were detected in a number of PAH-degrading Mycobacterium spp. isolated from various geographical locations. The operon differs from those of other Gram-positive bacteria in both the placement and orientation of the regulatory gene. In addition, the M. vanbaalenii PYR-1 pht operon contains no decarboxylase gene and none was identified within a 37 kb region containing the operon. This study is the first report of a phthalate degradation operon in Mycobacterium spp.