Macrophage-induced blood vessels guide Schwann cell-mediated regeneration of peripheral nerves

The peripheral nervous system has remarkable regenerative capacities in that it can repair a fully cut nerve. This requires Schwann cells to migrate collectively to guide regrowing axons across a 'bridge' of new tissue, which forms to reconnect a severed nerve. Here we show that blood vessels direct the migrating cords of Schwann cells. This multicellular process is initiated by hypoxia, selectively sensed by macrophages within the bridge, which via VEGF-A secretion induce a polarized vasculature that relieves the hypoxia. Schwann cells then use the blood vessels as "tracks" to cross the bridge taking regrowing axons with them. Importantly, disrupting the organization of the newly formed blood vessels in vivo, either by inhibiting the angiogenic signal or by re-orienting them, compromises Schwann cell directionality resulting in defective nerve repair. This study provides important insights into how the choreography of multiple cell-types is required for the regeneration of an adult tissue

Functional and regulatory profiling of energy metabolism in fission yeast

Background: The control of energy metabolism is fundamental for cell growth and function and anomalies in it are implicated in complex diseases and ageing. Metabolism in yeast cells can be manipulated by supplying different carbon sources: yeast grown on glucose rapidly proliferates by fermentation, analogous to tumour cells growing by aerobic glycolysis, whereas on non-fermentable carbon sources metabolism shifts towards respiration. Results: We screened deletion libraries of fission yeast to identify over 200 genes required for respiratory growth. Growth media and auxotrophic mutants strongly influenced respiratory metabolism. Most genes uncovered in the mutant screens have not been implicated in respiration in budding yeast. We applied gene-expression profiling approaches to compare steady-state fermentative and respiratory growth and to analyse the dynamic adaptation to respiratory growth. The transcript levels of most genes functioning in energy metabolism pathways are coherently tuned, reflecting anticipated differences in metabolic flows between fermenting and respiring cells. We show that acetyl-CoA synthase, rather than citrate lyase, is essential for acetyl-CoA synthesis in fission yeast. We also investigated the transcriptional response to mitochondrial damage by genetic or chemical perturbations, defining a retrograde response that involves the concerted regulation of distinct groups of nuclear genes that may avert harm from mitochondrial malfunction. Conclusions: This study provides a rich framework of the genetic and regulatory basis of energy metabolism in fission yeast and beyond, and it pinpoints weaknesses of commonly used auxotroph mutants for investigating metabolism. As a model for cellular energy regulation, fission yeast provides an attractive and complementary system to budding yeast

Determining the role of histone modification during Vaccinia virus infection

Vaccinia is a Poxvirus widely known as the vaccine used to eradicate Smallpox in 1980. Today, it is extensively used in research as an easy to work with biological tool. Unlike most viruses, it replicates in the cell cytoplasm and for decades it had been postulated that the nucleus is not necessary for viral infection. As a consequence, interactions between Vaccinia and the cell nucleus have been overlooked. Recently, some studies have shown that the virus recruits host cell nuclear proteins to replication factories in order to facilitate transcription. However, little is known about the extent and nature of poxvirus-nucleus interactions. We know that pathogens modulate cell chromatin, by controlling histone marks, in order to dampen the cell’s immune response. This project sheds light on the mechanisms used by Vaccinia to modulate host cell chromatin. We have special interest in how the virus may be preventing the expression of immune response genes. Using Immunofluorecence and Cell fractionation I have seen one phosphatase (H1) enter the cell nucleus during infection. A survey of histone modifications during the course of infection showed a drastic decrease in the phosphorylation of Histone 3 at Threonine 3, Serine 10, and Serine 28. As H3 S10 has been linked to cytokine gene repression I followed up this mark. I show, using in vitro dephosphorylation assays and cell transfections, that the Vaccinia phosphatase H1 is partially responsible for H3 S10 dephosphorylation. I further link this phenotype to dampening of the cellular immune response through reduction of cytokine gene expression. Finally, though modulation of H3 S10 phosphorylation I demonstrate that this modification is vital for productive Vaccinia infection

The regulation of the homeostasis and regeneration of peripheral nerve is distinct from the CNS and independent of a stem cell population

Peripheral nerves are highly regenerative, in contrast to the poor regenerative capabilities of the central nervous system (CNS). Here, we show that adult peripheral nerve is a more quiescent tissue than the CNS, yet all cell types within a peripheral nerve proliferate efficiently following injury. Moreover, whereas oligodendrocytes are produced throughout life from a precursor pool, we find that the corresponding cell of the peripheral nervous system, the myelinating Schwann cell (mSC), does not turn over in the adult. However, following injury, all mSCs can dedifferentiate to the proliferating progenitor-like Schwann cells (SCs) that orchestrate the regenerative response. Lineage analysis shows that these newly migratory, progenitor-like cells redifferentiate to form new tissue at the injury site and maintain their lineage, but can switch to become a nonmyelinating SC. In contrast, increased plasticity is observed during tumourigenesis. These findings show that peripheral nerves have a distinct mechanism for maintaining homeostasis and can regenerate without the need for an additional stem cell population.</p