Extreme genome diversity in the hyper-prevalent parasitic eukaryote Blastocystis

Blastocystis is the most prevalent eukaryotic microbe colonizing the human gut, infecting approximately 1 billion individuals worldwide. Although Blastocystis has been linked to intestinal disorders, its pathogenicity remains controversial because most carriers are asymptomatic. Here, the genome sequence of Blastocystis subtype (ST) 1 is presented and compared to previously published sequences for ST4 and ST7. Despite a conserved core of genes, there is unexpected diversity between these STs in terms of their genome sizes, guanine-cytosine (GC) content, intron numbers, and gene content. ST1 has 6,544 protein-coding genes, which is several hundred more than reported for ST4 and ST7. The percentage of proteins unique to each ST ranges from 6.2% to 20.5%, greatly exceeding the differences observed within parasite genera. Orthologous proteins also display extreme divergence in amino acid sequence identity between STs (i.e., 59%–61%median identity), on par with observations of the most distantly related species pairs of parasite genera. The STs also display substantial variation in gene family distributions and sizes, especially for protein kinase and protease gene families, which could reflect differences in virulence. It remains to be seen to what extent these inter-ST differences persist at the intra-ST level. A full 26% of genes in ST1 have stop codons that are created on the mRNA level by a novel polyadenylation mechanism found only in Blastocystis. Reconstructions of pathways and organellar systems revealed that ST1 has a relatively complete membrane-trafficking system and a near-complete meiotic toolkit, possibly indicating a sexual cycle. Unlike some intestinal protistan parasites, Blastocystis ST1 has near-complete de novo pyrimidine, purine, and thiamine biosynthesis pathways and is unique amongst studied stramenopiles in being able to metabolize ?-glucans rather than ?-glucans. It lacks all genes encoding heme-containing cytochrome P450 proteins. Predictions of the mitochondrion-related organelle (MRO) proteome reveal an expanded repertoire of functions, including lipid, cofactor, and vitamin biosynthesis, as well as proteins that may be involved in regulating mitochondrial morphology and MRO/endoplasmic reticulum (ER) interactions. In sharp contrast, genes for peroxisome-associated functions are absent, suggesting Blastocystis STs lack this organelle. Overall, this study provides an important window into the biology of Blastocystis, showcasing significant differences between STs that can guide future experimental investigations into differences in their virulence and clarifying the roles of these organisms in gut health and disease

Interdependence of the Peroxisome-targeting Receptors in Arabidopsis thaliana: PEX7 Facilitates PEX5 Accumulation and Import of PTS1 Cargo into Peroxisomes

In plants and mammals, the PEX7 PTS2 receptor relies on the PEX5 PTS1 receptor to shuttle proteins bearing peroxisome-targeting signals into peroxisomes. This study reveals that Arabidopsis pex7 mutants display defects not only in PTS2 import, but also in PEX5 accumulation and PTS1 import. Thus, PEX5 and PEX7 are interdependent in plants

Cytosolic phospholipase A₂alpha amplifies early cyclooxygenase-2 expression, oxidative stress and MAP kinase phosphorylation after cerebral ischemia in mice

<p>Abstract</p> <p>Background</p> <p>The enzyme cytosolic phospholipase A₂alpha (cPLA₂α) has been implicated in the progression of cerebral injury following ischemia and reperfusion. Previous studies in rodents suggest that cPLA₂α enhances delayed injury extension and disruption of the blood brain barrier many hours after reperfusion. In this study we investigated the role of cPLA₂α in early ischemic cerebral injury.</p> <p>Methods</p> <p>Middle cerebral artery occlusion (MCAO) was performed on cPLA₂α^+/+and cPLA₂α^-/-mice for 2 hours followed by 0, 2, or 6 hours of reperfusion. The levels of cPLA₂α, cyclooxygenase-2, neuronal morphology and reactive oxygen species in the ischemic and contralateral hemispheres were evaluated by light and fluorescent microscopy. PGE₂content was compared between genotypes and hemispheres after MCAO and MCAO and 6 hours reperfusion. Regional cerebral blood flow was measured during MCAO and phosphorylation of relevant MAPKs in brain protein homogenates was measured by Western analysis after 6 hours of reperfusion.</p> <p>Results</p> <p>Neuronal cPLA₂α protein increased by 2-fold immediately after MCAO and returned to pre-MCAO levels after 2 hours reperfusion. Neuronal cyclooxygenase-2 induction and PGE₂concentration were greater in cPLA₂α^+/+compared to cPLA₂α^-/-ischemic cortex. Neuronal swelling in ischemic regions was significantly greater in the cPLA₂α^+/+than in cPLA₂α^-/-brains (+/+: 2.2 ± 0.3 fold vs. -/-: 1.7 ± 0.4 fold increase; <it>P </it>< 0.01). The increase in reactive oxygen species following 2 hours of ischemia was also significantly greater in the cPLA₂α^+/+ischemic core than in cPLA₂α^-/-(+/+: 7.12 ± 1.2 fold vs. -/-: 3.1 ± 1.4 fold; <it>P </it>< 0.01). After 6 hours of reperfusion ischemic cortex of cPLA₂α^+/+, but not cPLA₂α^-/-, had disruption of neuron morphology and decreased PGE₂content. Phosphorylation of the MAPKs-p38, ERK 1/2, and MEK 1/2-was significantly greater in cPLA₂a^+/+than in cPLA₂α^-/-ischemic cortex 6 hours after reperfusion.</p> <p>Conclusions</p> <p>These results indicate that cPLA₂α modulates the earliest molecular and injury responses after cerebral ischemia and have implications for the potential clinical use of cPLA₂α inhibitors.</p