Heterozygous loss of Rbm24 in the adult mouse heart increases sarcomere slack length but does not affect function

Rbm24-mediated post-transcriptional regulation of skeletal and cardiac muscle development, function and regeneration

RNA-binding proteins are critically involved in the post-transcriptional control of gene expression during embryonic development and in adult life, contributing to regulating cell differentiation and maintaining tissue homeostasis. Compared to the relatively well documented functions of transcription factors, the regulatory roles of RNA-binding proteins in muscle development and function remain largely elusive. However, deficiency of many RNA-binding proteins has been associated with muscular defects, neuromuscular disorders and heart diseases, such as myotonic dystrophy, amyotrophic lateral sclerosis, and cardiomyopathy. Rbm24 is highly conserved among vertebrates and is one of the best characterized RNA-binding proteins with crucial implication in the myogenic and cardiomyogenic programs. It presents the distinctive particularity of displaying highly restricted expression in both skeletal and cardiac muscles, with changes in subcellular localization during the process of differentiation. Functional analyses using different vertebrate models have clearly demonstrated its requirement for skeletal muscle differentiation and regeneration as well as for myocardium organization and cardiac function, by regulating the expression of both common and distinct target genes in these tissues. The challenge remains to decipher the dynamic feature of post-transcriptional circuits regulated by Rbm24 during skeletal myogenesis, cardiomyogenesis, and muscle repair. This review discusses current understanding of its function in striated muscles and its possible implication in human disease, with the aim of identifying research gaps for future investigation.

Cardiomyocyte-specific Srsf3 deletion reveals a mitochondrial regulatory role

Serine-rich splicing factor 3 (SRSF3) was recently reported as being necessary to preserve RNA stability via an mTOR mechanism in a cardiac mouse model in adulthood. Here, we demonstrate the link between Srsf3 and mitochondrial integrity in an embryonic cardiomyocyte-specific Srsf3 conditional knockout (cKO) mouse model. Fifteen-day-old Srsf3 cKO mice showed dramatically reduced (below 50%) survival and reduced the left ventricular systolic performance, and histological analysis of these hearts revealed a significant increase in cardiomyocyte size, confirming the severe remodeling induced by Srsf3 deletion. RNA-seq analysis of the hearts of 5-day-old Srsf3 cKO mice revealed early changes in expression levels and alternative splicing of several transcripts related to mitochondrial integrity and oxidative phosphorylation. Likewise, the levels of several protein complexes of the electron transport chain decreased, and mitochondrial complex I-driven respiration of permeabilized cardiac muscle fibers from the left ventricle was impaired. Furthermore, transmission electron microscopy analysis showed disordered mitochondrial length and cristae structure. Together with its indispensable role in the physiological maintenance of mouse hearts, these results highlight the previously unrecognized function of Srsf3 in regulating the mitochondrial integrity.

RNA-Binding Protein Rbm24 as a Multifaceted Post-Transcriptional Regulator of Embryonic Lineage Differentiation and Cellular Homeostasis

RNA-binding proteins control the metabolism of RNAs at all stages of their lifetime. They are critically required for the post-transcriptional regulation of gene expression in a wide variety of physiological and pathological processes. Rbm24 is a highly conserved RNA-binding protein that displays strongly regionalized expression patterns and exhibits dynamic changes in subcellular localization during early development. There is increasing evidence that it acts as a multifunctional regulator to switch cell fate determination and to maintain tissue homeostasis. Dysfunction of Rbm24 disrupts cell differentiation in nearly every tissue where it is expressed, such as skeletal and cardiac muscles, and different head sensory organs, but the molecular events that are affected may vary in a tissue-specific, or even a stage-specific manner. Recent works using different animal models have uncovered multiple post-transcriptional regulatory mechanisms by which Rbm24 functions in key developmental processes. In particular, it represents a major splicing factor in muscle cell development, and plays an essential role in cytoplasmic polyadenylation during lens fiber cell terminal differentiation. Here we review the advances in understanding the implication of Rbm24 during development and disease, by focusing on its regulatory roles in physiological and pathological conditions.