Summary Myoblast fusion is essential for muscle development and regeneration. Yet, it remains poorly understood how mononucleated myoblasts fuse with preexisting fibers. We demonstrate that ERK1/2 inhibition (ERKi) induces robust differentiation and fusion of primary mouse myoblasts through a linear pathway involving RXR, ryanodine receptors, and calcium-dependent activation of CaMKII in nascent myotubes. CaMKII activation results in myotube growth via fusion with mononucleated myoblasts at a fusogenic synapse. Mechanistically, CaMKII interacts with and regulates MYMK and Rac1, and CaMKIIδ/γ knockout mice exhibit smaller regenerated myofibers following injury. In addition, the expression of a dominant negative CaMKII inhibits the formation of large multinucleated myotubes. Finally, we demonstrate the evolutionary conservation of the pathway in chicken myoblasts. We conclude that ERK1/2 represses a signaling cascade leading to CaMKII-mediated fusion of myoblasts to myotubes, providing an attractive target for the cultivated meat industry and regenerative medicine.

Calcium binding proteins (CBPs) function in response to changes in intracellular calcium (Ca 2+ ) levels by modulating intracellular signaling pathways. Calcium sensors, including Nucleobindins (Nucb1/2) undergo Ca 2+ -binding induced conformational changes and bind to target proteins.Nucleobindins possess additional uncharacterized domains including partly characterized EFhands. We study the molecular evolution of Nucleobindins in eukaryotes emphasizing on the Nterminal DNA binding domain (DBD) that emerged as a result of domain insertion event in Nucb1/2 domain-scaffold in an ancestor to the opisthokonts. Our results from in silico analyses and functional assays revealed that DBD of Nucb1 binds to canonical E-box sequences and triggers cell epithelial-mesenchymal transition (EMT). Thus, post gene duplication, Nucb1 has emerged as unconventional Ca 2+ -binding transcriptional regulators that can induce EMT. Highlights:1. Nucleobindins emerged from prokaryotic EF-hand containing protein.2. The DNA-binding domain was gained in these in opisthokonts.3. Gene duplication in ancestor of euteleostomes, lead to emergence of Nucb1/2. Nucb1 emerged as a canonical E-box binding protein promoting EMT

Eukaryotes employ a subset of dynamins to mediate mitochondrial fusion and fission dynamics. Here we report the molecular evolution and diversification of the dynamin‐related mitochondrial proteins that drive the fission (Drp1) and the fusion processes (mitofusin and OPA1). We demonstrate that the three paralogs emerged concurrently in an early mitochondriate eukaryotic ancestor. Furthermore, multiple independent duplication events from an ancestral bifunctional fission protein gave rise to specialized fission proteins. The evolutionary history of these proteins is marked by transformations that include independent gain and loss events occurring at the levels of entire genes, specific functional domains, and intronic regions. The domain level variations primarily comprise loss–gain of lineage specific domains that are present in the terminal regions of the sequences.

Significance Missense mutations in the TP53 gene, encoding the p53 tumor suppressor, are very frequent in human cancer. Some of those mutations, particularly the more common (“hotspot”) ones, not only abrogate p53’s tumor suppressor activities but also endow the mutant protein with oncogenic gain of function (GOF). We report that p53 R273H , the most common p53 mutant in pancreatic cancer, interacts with the SQSTM1/p62 protein to accelerate the degradation of cell adhesion proteins. This enables pancreatic cancer cells to detach from the epithelial sheet and engage in individualized cell migration, probably augmenting metastatic spread. By providing insights into mechanisms that underpin mutant p53 GOF, this study may suggest ways to interfere with the progression of cancers bearing particular p53 mutants.

Muscle regeneration is essential for vertebrate muscle homeostasis and recovery after injury. During regeneration, muscle stem cells differentiate into myocytes, which then fuse with pre-existing muscle fibres. Hence, differentiation, fusion and contraction must be tightly regulated during regeneration to avoid the disastrous consequences of premature fusion of myocytes to actively contracting fibres. Cytosolic calcium (Ca 2+ ), which is coupled to both induction of myogenic differentiation and contraction, has more recently been implicated in the regulation of myocyte-to-myotube fusion. In this viewpoint, we propose that Ca 2+ -mediated coordination of differentiation, fusion and contraction is a feature selected in the amniotes to facilitate muscle regeneration.