Sarcomere function activates a p53-dependent DNA damage response that promotes polyploidization and limits in vivo cell engraftment.

Human cardiac regeneration is limited by low cardiomyocyte replicative rates and progressive polyploidization by unclear mechanisms. To study this process, we engineer a human cardiomyocyte model to track replication and polyploidization using fluorescently tagged cyclin B1 and cardiac troponin T. Using time-lapse imaging, in vitro cardiomyocyte replication patterns recapitulate the progressive mononuclear polyploidization and replicative arrest observed in vivo. Single-cell transcriptomics and chromatin state analyses reveal that polyploidization is preceded by sarcomere assembly, enhanced oxidative metabolism, a DNA damage response, and p53 activation. CRISPR knockout screening reveals p53 as a driver of cell-cycle arrest and polyploidization. Inhibiting sarcomere function, or scavenging ROS, inhibits cell-cycle arrest and polyploidization. Finally, we show that cardiomyocyte engraftment in infarcted rat hearts is enhanced 4-fold by the increased proliferation of troponin-knockout cardiomyocytes. Thus, the sarcomere inhibits cell division through a DNA damage response that can be targeted to improve cardiomyocyte replacement strategies

Massively parallel disruption of enhancers active in human neural stem cells

Summary: Changes in gene regulation have been linked to the expansion of the human cerebral cortex and to neurodevelopmental disorders, potentially by altering neural progenitor proliferation. However, the effects of genetic variation within regulatory elements on neural progenitors remain obscure. We use sgRNA-Cas9 screens in human neural stem cells (hNSCs) to disrupt 10,674 genes and 26,385 conserved regions in 2,227 enhancers active in the developing human cortex and determine effects on proliferation. Genes with proliferation phenotypes are associated with neurodevelopmental disorders and show biased expression in specific fetal human brain neural progenitor populations. Although enhancer disruptions overall have weaker effects than gene disruptions, we identify enhancer disruptions that severely alter hNSC self-renewal. Disruptions in human accelerated regions, implicated in human brain evolution, also alter proliferation. Integrating proliferation phenotypes with chromatin interactions reveals regulatory relationships between enhancers and their target genes contributing to neurogenesis and potentially to human cortical evolution

RNA-Seq profiling of spinal cord motor neurons from a presymptomatic SOD1 ALS mouse.

Mechanisms involved with degeneration of motor neurons in amyotrophic lateral sclerosis (ALS; Lou Gehrig's Disease) are poorly understood, but genetically inherited forms, comprising ~10% of the cases, are potentially informative. Recent observations that several inherited forms of ALS involve the RNA binding proteins TDP43 and FUS raise the question as to whether RNA metabolism is generally disturbed in ALS. Here we conduct whole transcriptome profiling of motor neurons from a mouse strain, transgenic for a mutant human SOD1 (G85R SOD1-YFP), that develops symptoms of ALS and paralyzes at 5-6 months of age. Motor neuron cell bodies were laser microdissected from spinal cords at 3 months of age, a time when animals were presymptomatic but showed aggregation of the mutant protein in many lower motor neuron cell bodies and manifested extensive neuromuscular junction morphologic disturbance in their lower extremities. We observed only a small number of transcripts with altered expression levels or splicing in the G85R transgenic compared to age-matched animals of a wild-type SOD1 transgenic strain. Our results indicate that a major disturbance of polyadenylated RNA metabolism does not occur in motor neurons of mutant SOD1 mice, suggesting that the toxicity of the mutant protein lies at the level of translational or post-translational effects

ALX1‐related frontonasal dysplasia results from defective neural crest cell development and migration

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ALX1‐related frontonasal dysplasia results from defective neural crest cell development and migration

Abstract A pedigree of subjects presented with frontonasal dysplasia (FND). Genome sequencing and analysis identified a p.L165F missense variant in the homeodomain of the transcription factor ALX1 which was imputed to be pathogenic. Induced pluripotent stem cells (iPSC) were derived from the subjects and differentiated to neural crest cells (NCC). NCC derived from ALX1L165F/L165F iPSC were more sensitive to apoptosis, showed an elevated expression of several neural crest progenitor state markers, and exhibited impaired migration compared to wild‐type controls. NCC migration was evaluated in vivo using lineage tracing in a zebrafish model, which revealed defective migration of the anterior NCC stream that contributes to the median portion of the anterior neurocranium, phenocopying the clinical presentation. Analysis of human NCC culture media revealed a change in the level of bone morphogenic proteins (BMP), with a low level of BMP2 and a high level of BMP9. Soluble BMP2 and BMP9 antagonist treatments were able to rescue the defective migration phenotype. Taken together, these results demonstrate a mechanistic requirement of ALX1 in NCC development and migration

Integrative approaches generate insights into the architecture of non-syndromic cleft lip with or without cleft palate

Summary: Non-syndromic cleft lip with or without cleft palate (nsCL/P) is a common congenital facial malformation with a multifactorial etiology. Genome-wide association studies (GWASs) have identified multiple genetic risk loci. However, functional interpretation of these loci is hampered by the underrepresentation in public resources of systematic functional maps representative of human embryonic facial development. To generate novel insights into the etiology of nsCL/P, we leveraged published GWAS data on nsCL/P as well as available chromatin modification and expression data on mid-facial development. Our analyses identified five novel risk loci, prioritized candidate target genes within associated regions, and highlighted distinct pathways. Furthermore, the results suggest the presence of distinct regulatory effects of nsCL/P risk variants throughout mid-facial development and shed light on its regulatory architecture. Our integrated data provide a platform to advance hypothesis-driven molecular investigations of nsCL/P and other human facial defects

Differential expression of novel TARs in G85R motor neurons.

<p>A. RNA-Seq signal plots in reads per million mapped reads at the Limk1 gene from wild-type (black) and G85R (red) motor neurons. The canonical Limk1 gene map is shown at the top. The enlarged region shows a clear 3′-UTR extension in G85R motor neuron RNA. Similar data were observed for Gak (not shown). B. Validation of novel 3′-UTRs of Gak and Limk1 by qRT-PCR. Values are relative expression for each 3′-UTR in G85R versus wild-type motor neuron RNA.</p

RNA-Seq of laser capture microdissected spinal cord motor neurons from wtSOD1-YFP and G85R SOD1-YFP transgenic mice.

<p>A. Survival curve of G85R SOD1-YFP mice with copy number greater than 200. 80% of the mice were paralyzed (and euthanized) between ∼115 days and 205 days (red bar). N = 226. For the present study of motor neuron RNA, presymptomatic mice at ∼90 days of age were used. B.-D. Spinal cord from a 3 month old G85R SOD1-YFP mouse. Frozen section of right ventral horn region is shown, stained with Azure B dye, panel B (see Methods); incubated with anti-ChAT antibodies, panel C; or directly examined for YFP fluorescence, panel D. The large blue-stained cell bodies in panel B are motor neurons as indicated by anti-ChAT staining in panel C. Note that the same cells have YFP fluorescence in panel D. E. Large Azure B-stained cell bodies were laser captured directly into a guanidine thiocyanate solution (see Methods) and subsequent steps carried out as diagrammed (see Methods).</p

Differential expression in G85R motor neurons.

<p>A. Heatmap of selected genes from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053575#pone.0053575.s007" target="_blank">Table S2</a> significantly differentially expressed (raw p-value <0.005) between wild-type and G85R SOD1-YFP mice. For each gene listed, the ratio of RPKM values (G85R/WT) for individual pairs of biological replicates (Rep1, Rep2) is plotted according to the color code below. B. Validation of differentially expressed genes in G85R by qRT-PCR. Shown are box plots representing relative expression values of each gene in G85R versus wild-type motor neurons. Upper whisker represents top 25% of values, box represents the middle 50% of values, and lower whisker represents bottom 25% of values. Median value is indicated by horizontal dashed line. Statistical significance calculated by REST 2009 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053575#pone.0053575-Pfaffl1" target="_blank">[37]</a> is indicated by *  =  p<0.05, **  =  p<0.005, ***  =  p<0.0005. RNAs from at least three different mouse pairs were compared for each gene. Note that the Hsp110 and B2m validations used one exon-junction-spanning and one non-spanning primer set; minus reverse transcriptase controls for these samples were negative for DNA contamination. The expression changes in the left nine genes were validated with 0.19 ng of total RNA, while the remaining six were validated with 1.5 ng of total RNA.</p