Wound repair requires tight control of immune cell behavior, yet the mechanisms that restrain immune-driven wound repair responses remain poorly defined. Here, we demonstrate that rhomboid intramembrane serine protease Rhbdl2 influences wound repair in zebrafish. We generated rhbdl2 mutants using CRISPR-Cas9 and found that, although Rhbdl2 is dispensable for normal development, its loss triggers enhanced wound repair following injury. This regenerative phenotype is accompanied by increased macrophage migration speed and accumulation at the wound site, as well as elevated early apoptosis and cell proliferation. Proteomic analyses reveal increased Rac2 protein levels in rhbdl2 mutants, which was previously identified as a regulator of leukocyte motility. Functionally, Rac2 morpholino–mediated knockdown in rhbdl2 mutant larvae suppresses the elevated macrophage recruitment and enhanced tissue repair phenotype. Together, these findings identify Rhbdl2 as a modulator of macrophage recruitment to the wound site during tissue repair, with implications for inflammatory disease, fibrosis, and tumor–immune interactions.
Ribosome biogenesis occurs in the nucleolus, a biomolecular condensate whose material properties are thought to be important for function. However, the molecular basis of nucleolar dynamics and their relationship to ribosome assembly remain incompletely understood. We present a platform for high-throughput FRAP (HiT-FRAP) and use it to screen hundreds of genes for their impact on dynamics of the nucleolar scaffold nucleophosmin (NPM1). We find that NPM1 dynamics and nucleolar morphology are sensitive to ribosome assembly state: accumulation of early pre-ribosomal intermediates slows NPM1 dynamics and compacts the condensate, while accumulation of abortive late precursors accelerates dynamics and disrupts condensate integrity. These opposing biophysical states correlate with the strength of NPM1-pre-ribosome interactions. Importantly, mutations in the NPM1 intrinsically disordered region that alter pre-ribosome binding directly tune nucleolar dynamics. These results establish that ribosomal precursor assembly state determines nucleolar material properties through the strength of scaffold-pre-ribosome interactions and introduce HiT-FRAP as a platform for interrogating condensate dynamics broadly.
Ras-related GTPases are molecular switches regulating hundreds of signaling and trafficking pathways in cells. Many GTPase regulators remain to be identified despite extensive genetic and biochemical screens. Here we present the results of computational protein-protein interaction screens and functional experiments identifying the DENN domain protein Avl9 as a GTPase-activating protein for Arf1. Avl9 is involved in secretion and cell migration, but its molecular function has not been characterized. We determined that Avl9 possesses robust Arf-GAP activity and is recruited to secretory vesicles by Rab8. We find that Avl9 GAP function is conserved in humans and enhances cell migration. We propose that several other DENN domain proteins are also candidate GAPs, and we demonstrate that one candidate previously characterized as a Rab-GEF, DENND6A, exhibits strong Arf-GAP activity toward ARL8B, explaining its role in lysosome positioning. Collectively, this work uncovers a family of monomeric "DENN GAP" proteins that regulate diverse cell biological pathways.
Caveolae represent a prominent class of specialized membrane microdomains that are an abundant and striking feature of the sarcolemma of muscle cells. Loss or dysfunction of skeletal muscle caveolae can cause a spectrum of muscle diseases, including caveolinopathies associated with rippling muscle disease. Despite recent advances, the precise downstream mechanisms that link caveolar defects to muscle dysfunction are not resolved. In this review, we discuss the fundamental cell biology underpinning muscle diseases associated with caveolar disruption. We highlight how recent structural and functional advances in both muscle and non-muscle systems are providing crucial insights into these pathological processes. Specifically, we analyze how the loss of these abundant surface domains disrupts mechanoprotection, signal transduction, nanoscale lipid organization, and T-tubule biogenesis and function. Finally, we propose a unifying cell biological classification system for disease-associated variants of caveolin-3, with a view to providing a mechanistic framework to connect molecular defects with clinical phenotypes.
How deep into the cell do mechanical signals reach? In this issue, Bhaskar Naidu et al. (https://doi.org/10.1083/jcb.202510026) show that the Golgi responds to cell-spreading force and tunes its secretory output in a loop that feeds back to support spreading.
