Interactions between BRCA2 and RAD51 for promoting homologous recombination in Leishmania infantum

In most organisms, the primary function of homologous recombination (HR) is to allow genome protection by the faithful repair of DNA double-strand breaks. The vital step of HR is the search for sequence homology, mediated by the RAD51 recombinase, which is stimulated further by proteins mediators such as the tumor suppressor BRCA2. The biochemical interplay between RAD51 and BRCA2 is unknown in Leishmania or Trypanosoma. Here we show that the Leishmania infantum BRCA2 protein possesses several critical features important for the regulation of DNA recombination at the genetic and biochemical level. A BRCA2 null mutant, generated by gene disruption, displayed genomic instability and gene-targeting defects. Furthermore, cytological studies show that LiRAD51 can no longer localize to the nucleus in this mutant. The Leishmania RAD51 and BRCA2 interact together and the purified proteins bind single-strand DNA. Remarkably, LiBRCA2 is a recombination mediator that stimulates the invasion of a resected DNA double-strand break in an undamaged template by LiRAD51 to form a D-loop structure. Collectively, our data show that LiBRCA2 and LiRAD51 promote HR at the genetic and biochemical level in L. infantum, the causative agent of visceral leishmaniasis.     

Impact of colostomy on intestinal microflora and bacterial translocation in young rats fed with heat-killed Lactobacillus acidophilus strain LB

A rat animal model of left colostomy was found to significantly impair the growth curve of rats. Assessment of the intestinal flora showed that colostomy mostly affects the cecal but not colonic microflora. Generally, the number of enterococci was increased in both ileum and cecum; cecal lactobacilli also rose, accounting for a promotion of lactic acid bacteria in colostomised rats. No significant differences between colostomised, laparotomised and control rats could be observed for the translocation of intestinal bacteria to internal organs of rats (i.e. spleen, kidneys, lungs or liver), whatever their diet. Heat-killed Lactobacillus acidophilus strain LB administration (dead probiotic bacteria) tended to exhibit a stimulatory effect on bifidobacteria, probably affecting the culture-medium fermentation substances included in the pharmaceutical product. This effect was abolished by laparotomy and colostomy. A trend towards a probiotic-like effect, not susceptible to colostomy, was also witnessed as counts of lactobacilli tended to increase in both cecum and colon of all animals fed with L. acidophilus LB.     

Reintroduction of Nassella pulchra to California coastal grasslands: Effects of topsoil removal,plant neighbour removal and grazing

Question: What is the most appropriate combination of treatments to reintroduce Nassella pulchra, a perennial bunchgrass, into degraded mediterranean coastal grasslands? Location: Central coast of California, USA. Methods: N. pulchra was sown from seeds and transplanted into a degraded grassland in a multi‐factorial experiment testing the effects of (1) two grazing intensities (lightly grazed by native mammal species or ungrazed); (2) topsoil removal and (3) reduction of plant neighbours. The experiment was carried out on two types of surrounding vegetation (exotic annual grasses and exotic forbs). Results: Topsoil removal greatly enhanced establishment from seeds and transplant survival, mainly because it reduced the exotic vegetation and thus reduced competition. While removing neighbours was essential when topsoil was left intact, it had a negative effect on N. pulchra when surrounding species included exotic forbs (Brassica spec, and Asteraceae) at low density (after topsoil removal). Moderate grazing by native mammals (deer, rabbits and gophers) did not affect N. pulchra. Conclusion: Our results suggest that seeding after topsoil has been removed is a promising method to reintroduce N. pulchra to highly degraded sites where there is little to no native seed bank.     

Colonisation by native species of abandoned farmland adjacent to a remnant patch of Mediterranean steppe

We studied plant distribution at the margins (0–10 m) of three formerly cultivated plots adjacent to a remnant patch of the only Mediterranean steppe of France: La Crau. We sampled above-ground vegetation, seed bank, seed rain and seed dispersal by ants in order to assess the colonisation of steppe species at margins. Our results showed that (1) present day above-ground vegetation of formerly cultivated plots is influenced more by former agricultural practices (duration of melon cultivation, fertilisation) and time since abandonment than their position in relation to the steppe. (2) An edge effect was identified as the vegetation of the steppe (e.g. Thymus vulgaris, Salvia verbenaca, Linaria arvensis) colonises the formerly cultivated plots (coefficients of similarity between vegetation on margins and steppe vegetation decreased with distance from boundaries (r = -0.65, p < 0.001)). (3) Permanent deep seed bank (10-20 cm) did not contribute to either site or edge effects and was characterised by weed species from previous melon cultivation (e.g. Chenopodium album, Kicksia elatine, Portulaca oleracea, Solanum nigrum). (4) Seed rain density decreased with distance from edges (r = -0.39, p < 0.001) and seemed positively correlated to T. vulgaris cover. (5) The number of seeds in ant-traps seemed correlated to T. vulgaris cover. We concluded that after 19 years of abandonment, only about half of the steppe species have colonised just the few meters of the margins of the formerly cultivated plots and that restoration from seed bank, seed rain or seed dispersal by ants is unlikely. Our results are thus discussed within the context of restoring the steppe plant community on formerly cultivated plots.

     

Herbaceous plant diversity in forest ecosystems: patterns,mechanisms, and threats

Plant Ecology - Studies conducted in forests have resulted in much of the ecological theory we build upon today. However, our basic understanding of forest ecology comes almost exclusively from the...     

Characterization of the nonenzymatic chloramphenicol resistance (cmlA) gene of the In4 integron of Tn1696: similarity of the product to transmembrane transport proteins.

Integrons constitute a novel family of DNA elements which evolved by site-specific integration of discrete units between two conserved segments. On the In4 integron of Tn1696, a precisely inserted gene cassette of 1,549 bp conferring nonenzymatic chloramphenicol resistance (cmlA) is present between the streptomycin-spectinomycin resistance (aadA2) gene cassette and the 3'-conserved segment of the integron. In this study, we present the nucleotide sequence of the cmlA gene cassette of Tn1696, show its similarity to bacterial efflux systems and other transport proteins, and present evidence for alterations that its expression exerts on bacterial membranes. The cmlA gene cassette apparently carries its own promoter(s), a situation that has not heretofore been observed in the integrons of multiresistance plasmids and transposons of gram-negative bacteria. One or more of these promoters were shown to be functionally active in expressing a cat marker gene from promoter-probe vectors. The putative CmlA polypeptide appears to provoke a reduction of the content of the major porins OmpA and OmpC.     

Transvaginal transplantation of an extra egg to obtain twinning in cattle

An attempt was made to produce twin pregnancies by adding one ovum to the uterus of 17 cows presumed pregnant from insemination 5 to 10 days earlier. The ovum was placed in the uterine horn contralateral to the corpus luteum. All transferred eggs were'transported approximately 50 kilometers and were exposed to ambient temperature during the process of inovulation. Twin pregnancies occurred in 3 of 8 recipients having a naturally-occurring estrus. The ambient temperature was between 9° and 23°C, and the eggs were 6.5 to 8 days old. No pregnancies resulted in 9 cows brought into heat with prostaglandin. In this case the ambient temperature was 5–6°C and the eggs were 6 days old.