Comparative Genomics Suggests that the Fungal Pathogen Pneumocystis Is an Obligate Parasite Scavenging Amino Acids from Its Host's Lungs

Pneumocystis jirovecii is a fungus causing severe pneumonia in immuno-compromised patients. Progress in understanding its pathogenicity and epidemiology has been hampered by the lack of a long-term in vitro culture method. Obligate parasitism of this pathogen has been suggested on the basis of various features but remains controversial. We analysed the 7.0 Mb draft genome sequence of the closely related species Pneumocystis carinii infecting rats, which is a well established experimental model of the disease. We predicted 8’085 (redundant) peptides and 14.9% of them were mapped onto the KEGG biochemical pathways. The proteome of the closely related yeast Schizosaccharomyces pombe was used as a control for the annotation procedure (4’974 genes, 14.1% mapped). About two thirds of the mapped peptides of each organism (65.7% and 73.2%, respectively) corresponded to crucial enzymes for the basal metabolism and standard cellular processes. However, the proportion of P. carinii genes relative to those of S. pombe was significantly smaller for the “amino acid metabolism” category of pathways than for all other categories taken together (40 versus 114 against 278 versus 427, P<0.002). Importantly, we identified in P. carinii only 2 enzymes specifically dedicated to the synthesis of the 20 standard amino acids. By contrast all the 54 enzymes dedicated to this synthesis reported in the KEGG atlas for S. pombe were detected upon reannotation of S. pombe proteome (2 versus 54 against 278 versus 427, P<0.0001). This finding strongly suggests that species of the genus Pneumocystis are scavenging amino acids from their host's lung environment. Consequently, they would have no form able to live independently from another organism, and these parasites would be obligate in addition to being opportunistic. These findings have implications for the management of patients susceptible to P. jirovecii infection given that the only source of infection would be other humans

Male mating biology

Before sterile mass-reared mosquitoes are released in an attempt to control local populations, many facets of male mating biology need to be elucidated. Large knowledge gaps exist in how both sexes meet in space and time, the correlation of male size and mating success and in which arenas matings are successful. Previous failures in mosquito sterile insect technique (SIT) projects have been linked to poor knowledge of local mating behaviours or the selection of deleterious phenotypes during colonisation and long-term mass rearing. Careful selection of mating characteristics must be combined with intensive field trials to ensure phenotypic characters are not antagonistic to longevity, dispersal, or mating behaviours in released males. Success has been achieved, even when colonised vectors were less competitive, due in part to extensive field trials to ensure mating compatibility and effective dispersal. The study of male mating biology in other dipterans has improved the success of operational SIT programmes. Contributing factors include inter-sexual selection, pheromone based attraction, the ability to detect alterations in local mating behaviours, and the effects of long-term colonisation on mating competitiveness. Although great strides have been made in other SIT programmes, this knowledge may not be germane to anophelines, and this has led to a recent increase in research in this area

Targeted reprogramming of H3K27me3 resets epigenetic memory in plant paternal chromatin

Epigenetic marks are reprogrammed in the gametes to reset genomic potential in the next generation. In mammals, paternal chromatin is extensively reprogrammed through the global erasure of DNA methylation and the exchange of histones with protamines(1,2). Precisely how the paternal epigenome is reprogrammed in flowering plants has remained unclear since DNA is not demethylated and histones are retained in sperm(3,4). Here, we describe a multi-layered mechanism by which H3K27me3 is globally lost from histone-based sperm chromatin in Arabidopsis. This mechanism involves the silencing of H3K27me3 writers, activity of H3K27me3 erasers and deposition of a sperm-specific histone, H3.10 (ref. (5)), which we show is immune to lysine 27 methylation. The loss of H3K27me3 facilitates the transcription of genes essential for spermatogenesis and pre-configures sperm with a chromatin state that forecasts gene expression in the next generation. Thus, plants have evolved a specific mechanism to simultaneously differentiate male gametes and reprogram the paternal epigenome

Molecular Phylogeny and Biogeography of the Hawaiian Craneflies <i>Dicranomyia</i> (Diptera: Limoniidae)

<div><p>The Hawaiian Diptera offer an opportunity to compare patterns of diversification across large and small endemic radiations with varying species richness and levels of single island endemism. The craneflies (Limoniidae: <i>Dicranomyia</i>) represent a small radiation of 13 described species that have diversified within the Hawaiian Islands. We used Bayesian and maximum likelihood approaches to generate a molecular phylogeny of the Hawaiian <i>Dicranomyia</i> using a combination of nuclear and mitochondrial loci, estimated divergence times and reconstructed ancestral ranges. Divergence time estimation and ancestral range reconstruction suggest that the colonization that led to most of the diversity within the craneflies arrived prior to the formation of Kauai and demonstrates that the two major clades within that radiation contrast sharply in their patterns of diversification.</p></div