Mitochondrial transfer from mesenchymal stem cells improves neuronal metabolism after oxidant injury in vitro: The role of Miro1

Stroke-induced cerebral ischemia is a major cause of death and disability. The disruption of blood flow results in neuronal and glial cell death leading to brain injury. Reperfusion restores oxygen to the affected tissue, but can also cause damage through an enhanced oxidative stress and inflammatory response. This study examines mitochondrial transfer from MSC to neurons and the role it plays in neuronal preservation after oxidant injury. We observed the transfer of mitochondria from MSC to mouse neurons in vitro following hydrogen peroxide exposure. The observed transfer was dependent on cell-to-cell contact and led to increased neuronal survival and improved metabolism. A number of pro-inflammatory and mitochondrial motility genes were upregulated in neurons after hydrogen peroxide exposure. This included Miro1 and TNFAIP2, linking inflammation and mitochondrial transfer to oxidant injury. Increasing Miro1 expression in MSC improved the metabolic benefit of mitochondrial transfer after neuronal oxidant injury. Decreasing Miro1 expression had the opposite effect, decreasing the metabolic benefit of MSC co-culture. MSC transfer of mitochondria to oxidant-damaged neurons may help improve neuronal preservation and functional recovery after stroke.

The putative phospholipase Lip2 counteracts oxidative damage and influences the virulence of Ustilago maydis

Ustilago maydis is an obligate biotrophic fungal pathogen which causes common smut disease of corn. To proliferate in host tissue, U. maydis must gain access to nutrients and overcome plant defence responses, such as the production of reactive oxygen species. The elucidation of the mechanisms by which U. maydis meets these challenges is critical for the development of strategies to combat smut disease. In this study, we focused on the contributions of phospholipases (PLs) to the pathogenesis of corn smut disease. We identified 11 genes encoding putative PLs and characterized the transcript levels for these genes in the fungus grown in culture and during infection of corn tissue. To assess the contributions of specific PLs, we focused on two genes, lip1 and lip2, which encode putative phospholipase A₂ (PLA₂ ) enzymes with similarity to platelet-activating factor acetylhydrolases. PLA₂ enzymes are known to counteract oxidative damage to lipids in other organisms. Consistent with a role in the mitigation of oxidative damage, lip2 mutants were sensitive to oxidative stress provoked by hydrogen peroxide and by increased production of reactive oxygen species caused by inhibitors of mitochondrial functions. Importantly, mutants defective in lip2, but not lip1, were attenuated for virulence in corn seedlings. Finally, a comparative analysis of fatty acid and cardiolipin profiles in the wild-type strain and a lip2 mutant revealed differences consistent with a protective role for Lip2 in maintaining lipid homeostasis and mitochondrial health during proliferation in the hostile host environment.

Investigating the Ustilago maydis/Zea mays pathosystem: transcriptional responses and novel functional aspects of a fungal calcineurin regulatory B subunit

The sustainable control of basidiomycete biotrophic plant pathogenesis requires an understanding of host responses to infection, as well as the identification and functional analysis of fungal genes involved in disease development. The creation and analysis of a suppressive subtractive hybridization (SSH) cDNA library from Ustilago maydis-infected Zea mays seedlings enabled the identification of fungal and plant genes expressed during disease development, and uncovered new insights into the interactions of this model system. Candidate U. maydis pathogenesis genes were identified by using the current SSH cDNA library analysis, and by knowledge generated from previous cDNA microarray and comparative genomic analyses. These identifications were supported by the independent determination of transcript level changes in different cell-types and during pathogenic development. The basidiomycete specific um01632, the highly in planta expressed um03046 (zig1), and the calcineurin regulatory B subunit (um10226, cnb1), were chosen for deletion experiments. um01632 and zig1 mutants showed no difference in morphology and did not have a statistically significant impact on pathogenesis. cnb1 mutants had a distinct cell division phenotype and reduced virulence in seedling assays. Infections with reciprocal wild-type×Δcnb1 haploid strain crosses revealed that the wild-type allele was unable to fully compensate for the lack of a second cnb1 allele. This haploinsufficiency was undetected in other fungal cnb1 mutational analyses. The reported data improves U. maydis genome annotation and expands on the current understanding of pathogenesis genes in this model basidiomycete.

The Complete Genome Sequence of Methanobrevibacter sp. AbM4

Methanobrevibacter sp. AbM4 was originally isolated from the abomasal contents of a sheep and was chosen as a representative of the Methanobrevibacter wolinii clade for genome sequencing. The AbM4 genome is smaller than that of the rumen methanogen M. ruminantium M1 (2.0 Mb versus 2.93 Mb), encodes fewer open reading frames (ORFs) (1,671 versus 2,217) and has a lower G+C percentage (29% versus 33%). Overall, the composition of the AbM4 genome is very similar to that of M1 suggesting that the methanogenesis pathway and central metabolism of these strains are highly similar, and both organisms are likely to be amenable to inhibition by small molecule inhibitors and vaccine-based methane mitigation technologies targeting these conserved features. The main differences compared to M1 are that AbM4 has a complete coenzyme M biosynthesis pathway and does not contain a prophage or non-ribosomal peptide synthase genes. However, AbM4 has a large CRISPR region and several type I and type II restriction-modification system components. Unusually, DNA-directed RNA polymerase B' and B'' subunits of AbM4 are joined, a feature only previously observed in some thermophilic archaea. AbM4 has a much reduced complement of genes encoding adhesin-like proteins which suggests it occupies a ruminal niche different from that of M1.

Quantification of progeny classes in two facultatively apomictic accessions of Hieracium

Hieracium is an established model system for studying the cytological and genetic basis of gametophytic apomixis. In common with most known apomicts, the formation of 'maternal seed' is not exclusive in Hieracium, as apomixis operates in conjunction with a low level of sexuality. When this occurs the form of apomixis is described as 'facultative'. The formation of maternal seed in these plants is characterised by the avoidance of meiosis followed by the parthenogenetic development of an unreduced egg cell. In some ovules, however, meiosis does proceed, and sometimes the fertilisation of an egg cell presages embryogenesis. As a result, this mechanism of facultative apomixis leads to the formation of several different types of progeny, each representing a unique combination of meiosis/apomeiosis and fertilisation/parthenogenesis. Furthermore, fertilisation may involve either self or non-self pollen, leading to the recognition of six progeny classes from each individual plant. To facilitate an understanding of these processes we have developed a method for identifying individuals from different progeny classes based on the inheritance of introduced heterologous marker genes. This technique permits the screening of many thousands of seedlings at germination, and the consequent isolation of individuals associated with rare classes. Progeny profiles were determined for two apomictic accessions of Hieracium. Both were found to develop approximately 2.5% of their seed from meiotically derived eggs under the experimental conditions used and to have a rate of hybridity of approximately 2%. Evidence was also found for the action of a self-incompatibility mechanism operating in these plants despite the autonomous nature of apomixis in Hieracinum. As a demonstration of the utility of this approach, a study was conducted of polyembryony in one accession. The results indicate that there was a 7 fold greater likelihood that a meiotically derived seedling would arise in a polyembryonic seed than in a single-embryo seed. This indicates that facultative apomixis in Hieracium not only results from the simultaneous occurrence of sexual and asexual seed formation in the same capitulum as previously demonstrated, but most often as parallel processes within the same ovule.