Transcriptional profiling of differentially vulnerable motor neurons at pre-symptomatic stage in the Smn (2b/-) mouse model of spinal muscular atrophy

INTRODUCTION: The term motor neuron disease encompasses a spectrum of disorders in which motor neurons are the lost. Importantly, while some motor neurons are lost early in disease and others remain intact at disease end-stage. This creates a valuable experimental paradigm to investigate the factors that regulate motor neuron vulnerability. Spinal muscular atrophy is a childhood motor neuron disease caused by mutations or deletions in the SMN1 gene. Here, we have performed transcriptional analysis on differentially vulnerable motor neurons from an intermediate mouse model of Spinal muscular atrophy at a presymptomatic time point. RESULTS: We have characterised two differentially vulnerable populations, differing in the level neuromuscular junction loss. Transcriptional analysis on motor neuron cell bodies revealed that reduced Smn levels correlate with a reduction of transcripts associated with the ribosome, rRNA binding, ubiquitination and oxidative phosphorylation. Furthermore, P53 pathway activation precedes neuromuscular junction loss, suggesting that denervation may be a consequence, rather than a cause of motor neuron death in Spinal muscular atrophy. Finally, increased vulnerability correlates with a decrease in the positive regulation of DNA repair. CONCLUSIONS: This study identifies pathways related to the function of Smn and associated with differential motor unit vulnerability, thus presenting a number of exciting targets for future therapeutic development. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s40478-015-0231-1) contains supplementary material, which is available to authorized users

Conditioned spin and charge dynamics of a single electron quantum dot

In this article we describe the incoherent and coherent spin and charge dynamics of a single electron quantum dot. We use a stochastic master equation to model the state of the system, as inferred by an observer with access to only the measurement signal. Measurements obtained during an interval of time contribute, by a past quantum state analysis, to our knowledge about the system at any time $t$ within that interval. Such analysis permits precise estimation of physical parameters, and we propose and test a modification of the classical Baum-Welch parameter re-estimation method to systems driven by both coherent and incoherent processes.Comment: 9 pages, 9 figure

A novel whole-cell lysate kinase assay identifies substrates of the p38 MAPK in differentiating myoblasts

<p>Abstract</p> <p>Background</p> <p>The p38α mitogen-activated protein kinase (MAPK) is a critical mediator of myoblast differentiation, and does so in part through the phosphorylation and regulation of several transcription factors and chromatin remodelling proteins. However, whether p38α is involved in processes other than gene regulation during myogenesis is currently unknown, and why other p38 isoforms cannot compensate for its loss is unclear.</p> <p>Methods</p> <p>To further characterise the involvement of p38α during myoblast differentiation, we developed and applied a simple technique for identifying relevant <it>in vivo </it>kinase substrates and their phosphorylation sites. In addition to identifying substrates for one kinase, the technique can be used <it>in vitro </it>to compare multiple kinases in the same experiment, and we made use of this to study the substrate specificities of the p38α and β isoforms.</p> <p>Results</p> <p>Applying the technique to p38α resulted in the identification of seven <it>in vivo </it>phosphorylation sites on six proteins, four of which are cytoplasmic, in lysate derived from differentiating myoblasts. An <it>in vitro </it>comparison with p38β revealed that substrate specificity does not discriminate these two isoforms, but rather that their distinguishing characteristic appears to be cellular localisation.</p> <p>Conclusion</p> <p>Our results suggest p38α has a novel cytoplasmic role during myogenesis and that its unique cellular localisation may be why p38β and other isoforms cannot compensate for its absence. The substrate-finding approach presented here also provides a necessary tool for studying the hundreds of protein kinases that exist and for uncovering the deeper mechanisms of phosphorylation-dependent cell signalling.</p

The Proteolipid Protein Promoter Drives Expression outside of the Oligodendrocyte Lineage during Embryonic and Early Postnatal Development

The proteolipid protein (Plp) gene promoter is responsible for driving expression of one of the major components of myelin – PLP and its splice variant DM-20. Both products are classically thought to express predominantly in oligodendrocytes. However, accumulating evidence suggests Plp expression is more widespread than previously thought. In an attempt to create a mouse model for inducing oligodendrocyte-specific gene deletions, we have generated transgenic mice expressing a Cre recombinase cDNA under control of the mouse Plp promoter. We demonstrate Plp promoter driven Cre expression is restricted predominantly to mature oligodendrocytes of the central nervous system (CNS) at postnatal day 28. However, crosses into the Rosa26LacZ and mT/mG reporter mouse lines reveal robust and widespread Cre activity in neuronal tissues at E15.5 and E10.5 that is not strictly oligodendrocyte lineage specific. By P28, all CNS tissues examined displayed high levels of reporter gene expression well outside of defined white matter zones. Importantly, our study reinforces the emerging idea that Plp promoter activity is not restricted to the myelinating cell lineage, but rather, has widespread activity both during embryonic and early postnatal development in the CNS. Specificity of the promoter to the oligodendrocyte cell lineage, as shown through the use of a tamoxifen inducible Plp-CreERt line, occurs only at later postnatal stages. Understanding the temporal shift in Plp driven expression is of consequence when designing experimental models to study oligodendrocyte biology

Abnormal fatty acid metabolism is a core component of spinal muscular atrophy

Objective: Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder leading to paralysis and subsequent death in young children. Initially considered a motor neuron disease, extra-neuronal involvement is increasingly recognized. The primary goal of this study was to investigate alterations in lipid metabolism in SMA patients and mouse models of the disease. Methods: We analyzed clinical data collected from a large cohort of pediatric SMA type I-III patients as well as SMA type I liver necropsy data. In parallel, we performed histology, lipid analysis, and transcript profiling in mouse models of SMA. Results: We identify an increased susceptibility to developing dyslipidemia in a cohort of 72 SMA patients and liver steatosis in pathological samples. Similarly, fatty acid metabolic abnormalities were present in all SMA mouse models studied. Specifically, Smn2B/- mice displayed elevated hepatic triglycerides and dyslipidemia, resembling non-alcoholic fatty liver disease (NAFLD). Interestingly, this phenotype appeared prior to denervation. Interpretation: This work highlights metabolic abnormalities as an important feature of SMA, suggesting implementation of nutritional and screening guidelines in patients, as such defects are likely to increase metabolic distress and cardiovascular risk. This study emphasizes the need for a systemic therapeutic approach to ensure maximal benefits for all SMA patients throughout their life

Functional analysis of LAP2 beta, gamma and o during the development of zebrafish (Danio rerio)

Three isoforms of the lamina-associated polypeptide 2 (LAP2) family, have been identified in zebrafish (Danio rerio). Zebrafish LAP2 (ZLAP2) beta, gamma and o have identical aminoterminal regions containing the LEM domain. A lamina binding domain and a membrane spanning sequence are also present in the carboxyterminal region. The maternally synthesized ZLAP2o is the biggest of the three isoforms and is detected as a polypeptide of Mr 84 000. The somatic isoforms, ZLAP2beta and gamma are represented as smaller polypeptides of Mr 66 000 and 45 000 respectively. Western and northern blot analysis indicated that ZLAP2o is the only LAP2 present in early embryonic stages up to the gastrula stage. With the progression of embryonic development, the amount of ZLAP2o decreased whereas the amount of somatic isoforms ZLAP2beta and gamma) increased. Using immunofluorescence on somatic cells, ZLAP2beta and gamma are observed at the nuclear periphery in interphase cells. A cytoplasmic distribution appeared in late prometaphase and the isoforms are located at the surface of segregated chromosomes in late anaphase. However, during early embryonic development, ZLAP2o is associated with mitotic chromosomes prior to anaphase and the formation of karyomere is also observed. Using the morpholino technology, knock-down experiments on ZLAP2 during the zebrafish development suggest a strong correlation between the loss of ZLAP2 expression and abnormal phenotypes observed 24 hours post-fertilization. Altogether, my data indicate that ZLAP2 proteins may play a key role in early developmental events

Blood Flow to the Spleen is Altered in a Mouse Model of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disorder affecting young children. While pre-clinical models of SMA show small spleens, the same is not true in humans. Here, we show by doppler ultrasonography decreased splenic blood flow in Smn(2B/-) mice. Further, AAV9-SMN gene therapy does not rescue the distal ear and tail necrosis nor the spleen size in these mice, suggesting that the latter may be linked to a cardiovascular defect. Absence of smaller spleens in human patients is likely due to differences in presentation of defects in SMA between pre-clinical mouse models and human patients, particularly the susceptibility to cardiovascular issues

Additional file 1: Table S1. of Transcriptional profiling of differentially vulnerable motor neurons at pre-symptomatic stage in the Smn 2b/- mouse model of spinal muscular atrophy

Table shows a summary of the sequencing data obtained from the RNAseq analysis, as analysed using Tophat software. Table show the number of reads (reads), the percentage which mapped to a unique location (% unique), the percentage which mapped to a distinct location (% distinct), the number of mapped location (mapped locations), the number of mapped reads (mapped reads) and the percentage of 10.1186/s40478-015-0231-1 reads which were mapped (% mapped) for each of the 8 samples. (DOCX 53 kb