Caenorhabditis elegansmodels for striated muscle disorders caused by missense variants of humanLMNA

Abstract

AbstractStriated muscle laminopathies caused by missense mutations in the nuclear lamin geneLMNAare characterized by cardiac dysfunction and often skeletal muscle defects. Attempts to predict whichLMNAvariants are pathogenic and to understand their physiological effects lags behind variant discovery. We createdCaenorhabditis elegansmodels for striated muscle laminopathies by introducing pathogenic humanLMNAvariants and variants of unknown significance at conserved residues within thelmn-1gene. Severe missense variants reduced fertility and/or motility inC. elegans. Nuclear morphology defects were evident in the hypodermal nuclei of many lamin variant strains, indicating a loss of nuclear envelope integrity. Phenotypic severity varied within the two classes of missense mutations involved in striated muscle disease, but overall, variants associated with both skeletal and cardiac muscle defects in humans lead to more severe phenotypes in our model than variants predicted to disrupt cardiac function alone. We also identified a separation of function allele,lmn-1(R204W), that exhibited normal viability and swimming behavior but had a severe nuclear migration defect. Thus, we establishedC. elegansavatars for striated muscle laminopathies and identifiedLMNAvariants that offer insight into lamin mechanisms during normal development.Author summaryMuscular dystrophy is a progressive muscle-wasting disorder that eventually leads to cardiac disease. Mutations in theLMNAgene, which encodes an intermediate filament protein involved in the structure and organization of the nucleus, is a common but poorly understood cause of this disease. How variants across the breadth ofLMNAcontribute to mechanistic cellular defects that lead to disease is poorly understood, leading to hurdles in diagnosing disease and developing treatments. We found that by introducing amino acid substitutions found in patients with striated muscle disorders caused byLMNAinto the conservedlmn-1gene of the nematodeC. elegans, we could rapidly test the function of these variants to better understand their roles. We found that variants modeling diseases that involve both skeletal and cardiac muscle in humans were the most pathogenic inC. elegans, typically affecting both viability and movement, while those that modeled cardiac disease alone had less deleterious effects inC. elegans. Furthermore, we uncovered molecular mechanisms for how lamins interact with other nuclear envelope proteins to carry out their cellular functions. Thus, our newC. elegansmodels can be used to diagnose and predict the severity of new variants of humanLMNAas well as better understanding the molecular mechanisms of lamins in normal development.