Myosin VI regulates the spatial organisation of mammalian transcription initiation.

During transcription, RNA Polymerase II (RNAPII) is spatially organised within the nucleus into clusters that correlate with transcription activity. While this is a hallmark of genome regulation in mammalian cells, the mechanisms concerning the assembly, organisation and stability remain unknown. Here, we have used combination of single molecule imaging and genomic approaches to explore the role of nuclear myosin VI (MVI) in the nanoscale organisation of RNAPII. We reveal that MVI in the nucleus acts as the molecular anchor that holds RNAPII in high density clusters. Perturbation of MVI leads to the disruption of RNAPII localisation, chromatin organisation and subsequently a decrease in gene expression. Overall, we uncover the fundamental role of MVI in the spatial regulation of gene expression

In Mitochondria β-Actin Regulates mtDNA Transcription and Is Required for Mitochondrial Quality Control

Summary: In eukaryotic cells, actin regulates both cytoplasmic and nuclear functions. However, whether actin-based structures are present in the mitochondria and are involved in mitochondrial functions has not been investigated. Here, using wild-type β-actin +/+ and knockout (KO) β-actin −/− mouse embryonic fibroblasts we show evidence for the defect in maintaining mitochondrial membrane potential (MMP) in β-actin-null cells. MMP defects were associated with impaired mitochondrial DNA (mtDNA) transcription and nuclear oxidative phosphorylation (OXPHOS) gene expression. Using super-resolution microscopy we provided direct evidence on the presence of β-actin-containing structures inside mitochondria. Large aggregates of TFAM-stained nucleoids were observed in bulb-shaped mitochondria in KO cells, suggesting defects in mitochondrial nucleoid segregation without β-actin. The observation that mitochondria-targeted β-actin rescued mtDNA transcription and MMP suggests an indispensable functional role of a mitochondrial β-actin pool necessary for mitochondrial quality control. : Molecular Biology; Cell Biology; Functional Aspects of Cell Biology Subject Areas: Molecular Biology, Cell Biology, Functional Aspects of Cell Biolog

Transcriptional Profiling Reveals Ribosome Biogenesis, Microtubule Dynamics and Expression of Specific lncRNAs to be Part of a Common Response to Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are short peptides that are able to efficiently penetrate cellular lipid bilayers. Although CPPs have been used as carriers in conjugation with certain cargos to target specific genes and pathways, how rationally designed CPPs per se affect global gene expression has not been investigated. Therefore, following time course treatments with 4 CPPs-penetratin, PepFect14, mtCPP1 and TP10, HeLa cells were transcriptionally profiled by RNA sequencing. Results from these analyses showed a time-dependent response to different CPPs, with specific sets of genes related to ribosome biogenesis, microtubule dynamics and long-noncoding RNAs being differentially expressed compared to untreated controls. By using an image-based high content phenotypic profiling platform we confirmed that differential gene expression in CPP-treated HeLa cells strongly correlates with changes in cellular phenotypes such as increased nucleolar size and dispersed microtubules, compatible with altered ribosome biogenesis and cell growth. Altogether these results suggest that cells respond to different cell penetrating peptides by alteration of specific sets of genes, which are possibly part of the common response to such stimulus