The core spliceosomal factor U2AF1 controls cell-fate determination via the modulation of transcriptional networks

The emerging significance of splicing in vertebrate development

Splicing is a crucial regulatory node of gene expression that has been leveraged to expand the proteome from a limited number of genes. Indeed, the vast increase in intron number that accompanied vertebrate emergence might have aided the evolution of developmental and organismal complexity. Here, we review how animal models for core spliceosome components have provided insights into the role of splicing in vertebrate development, with a specific focus on neuronal, neural crest and skeletal development. To this end, we also discuss relevant spliceosomopathies, which are developmental disorders linked to mutations in spliceosome subunits. Finally, we discuss potential mechanisms that could underlie the tissue-specific phenotypes often observed upon spliceosome inhibition and identify gaps in our knowledge that, we hope, will inspire further research.

Heat Shock Alters the Proteomic Profile of Equine Mesenchymal Stem Cells

The aim of this research was to determine the impact of heat stress on cell differentiation in an equine mesenchymal stem cell model (EMSC) through the application of heat stress to primary EMSCs as they progressed through the cell specialization process. A proteomic analysis was performed using mass spectrometry to compare relative protein abundances among the proteomes of three cell types: progenitor EMSCs and differentiated osteoblasts and adipocytes, maintained at 37 °C and 42 °C during the process of cell differentiation. A cell-type and temperature-specific response to heat stress was observed, and many of the specific differentially expressed proteins were involved in cell-signaling pathways such as Notch and Wnt signaling, which are known to regulate cellular development. Furthermore, cytoskeletal proteins profilin, DSTN, SPECC1, and DAAM2 showed increased protein levels in osteoblasts differentiated at 42 °C as compared with 37 °C, and these cells, while they appeared to accumulate calcium, did not organize into a whorl agglomerate as is typically seen at physiological temperatures. This altered proteome composition observed suggests that heat stress could have long-term impacts on cellular development. We propose that this in vitro stem cell culture model of cell differentiation is useful for investigating molecular mechanisms that impact cell development in response to stressors.

Mutant U2AF1-induced differential alternative splicing causes an oxidative stress in bone marrow stromal cells

Alternative splicing (AS) is a critical regulatory process of gene expression. In bone marrow microenvironment, AS plays a critical role in mesenchymal stem cells fate determination by forming distinct isoforms of important regulators. As a spliceosome factor, U2AF1 is essential for the catalysis of pre-mRNA splicing, and its mutation can cause differential AS events. In the present study, by forced expression of mutant U2AF1 (U2AF1S34F) in the mouse bone marrow stroma OP9 cells, we determine AS changes in U2AF1S34F transduced OP9 cells and investigate their role in stroma cell biological functions. We find that abundant differential RNA splicing events are induced by U2AF1S34F in OP9 cells. U2AF1S34F causes increased generation of hydrogen peroxide, promotes production of cytokines and chemokines. U2AF1S34F transduced OP9 cells also exhibit dysfunction of mitochondria. RNA-seq data, gene ontology (GO), and gene set enrichment analysis reveal that differentially expressed genes downregulated in response to U2AF1S34F are enriched in peroxisome component and function. U2AF1S34F can also cause release of hydrogen peroxide from OP9 cells. Furthermore, we investigate the influence of U2AF1S34F-induced oxidative stress in stromal cells on hematopoietic cells. When co-culturing mouse bone marrow mononuclear cells with OP9 cells, the U2AF1S34F expressing OP9 cells induce phosphorylation of histone H2AX in hematopoietic cells. Collectively, our results reveal that mutant U2AF1-induced differential AS events cause oxidative stress in bone marrow stromal cells and can further lead to DNA damage and genomic instability in hematopoietic cells.

Alternative splicing in mesenchymal stem cell differentiation

The differentiation and maturation of mesenchymal stem cells (MSCs) to mesodermal and other lineages are known to be controlled by various extrinsic and intrinsic signals. The dysregulation of the MSC differentiation balance has been linked to several pathophysiological conditions, including obesity and osteoporosis. Previous research of the molecular mechanisms governing MSC differentiation has mostly focused on transcriptional regulation. However, recent findings are revealing the underrated role of alternative splicing (AS) in MSC differentiation and functions. In this review, we discuss recent progress in elucidating the regulatory roles of AS in MSC differentiation. We catalogue and highlight the key AS events that modulate MSC differentiation to major osteocytes, chondrocytes, and adipocytes, and discuss the regulatory mechanisms by which AS is regulated.