Biology subjects

Mella, J.

Publications and source records attributed to Mella, J..

3 recordsLinked to original sources

bioRxiv2026

Cardiomyocyte vulnerability to lamin polymer disruption revealed by saturation mutagenesis

Hundreds of mutations to the broadly expressed LMNA gene cause disease primarily within cardiac, muscular, and adipose tissues (1). Tissue-specific pathogenesis arises when mutant protein dysfunction collides with the unique demands of a specific cell type. Here, we decipher the cell-type-specific consequences of ~15,000 LMNA mutations by completing the first saturation mutagenesis screens in human induced pluripotent cells (hiPSCs) and hiPSC-derived cardiomyocytes using our newly developed single large serine integrase cassette exchange (SLICE) platform. We find that destabilization is a predominant consequence of pathogenic LMNA mutations, is selected against in human populations, and is associated with cardiomyopathy. Mutation sensitivity maps reveal Lamin A quality control at both the subunit and multimer level, resolve lateral and head-to-tail polymerization interfaces, and uncover a convergence between disruption of lamin polymer assembly and pathogenesis. Uniquely in cardiomyocytes, lamin A polymer assembly defects drive profound protein loss, nuclear abnormalities, and cellular toxicity, explaining the origins of cardiac specificity in laminopathy syndromes.

cell biology↗

bioRxiv2026

Emerin loss of function inhibits MyoD-driven differentiation of human iPSCs into skeletal myotubes

Loss of function of the nuclear lamina-associated protein emerin causes Emery-Dreifuss muscular dystrophy (EDMD). Efforts to define emerins essential functions in skeletal muscle have been limited by poor concordance between mouse models and human disease phenotypes. Here, we adapt transgene-driven differentiation of human induced pluripotent stem cells (hiPSCs) into skeletal muscle (iSMs) as a tractable human model for emerin loss of function. We find that EMD knockout (KO) hiPSCs are poorly responsive to combined overexpression of MyoD and Baf60c and produce fewer mature iSMs, indicating that emerin influences muscle differentiation downstream of these differentiation factors. While MyoD acetylation and heterodimerization with E-box proteins are unaffected by emerin loss, MyoD targets including p21 and myogenin are downregulated, and EMD KO cells exhibit impaired cell cycle exit in response to differentiation signals. Transcriptomic analysis of EMD KO iSMs revealed persistent expression of cell cycle genes and decreased expression of terminal muscle differentiation genes. Dysregulated genes do not overlap with lamina-associated domains (LADs) but are instead enriched for targets of polycomb repressive complex 2 (PRC2), which deposits H3K27 trimethylation. Altogether, our data indicate a functional overlap between emerin and PRC2-mediated regulation of terminal muscle differentiation.

cell biology↗

bioRxiv2025

C-terminal tagging, transmembrane domain hydrophobicity, and an ER retention motif influence the secretory trafficking of the inner nuclear membrane protein emerin

The inner nuclear membrane (INM), a subdomain of the endoplasmic reticulum (ER), sequesters hundreds of transmembrane proteins within the nucleus. We previously found that one INM protein, emerin, can evade the INM by secretory transport to the lysosome, where it is degraded. In this work, we used targeted mutagenesis to identify intrinsic sequences that promote or inhibit emerins secretory trafficking. By manipulating these sequences across several tag and expression level combinations, we now find that emerins localization is sensitive to C-terminal GFP tagging. While emerins long, hydrophobic C-terminal transmembrane domain facilitates trafficking to the lysosome, extending its lumenal terminus with a GFP tag biases the protein toward this pathway. In contrast, we identify a conserved ER retention sequence that stabilizes N- and C-terminally tagged emerin by limiting its lysosomal flux. These findings underscore long- standing concerns about tagging artifacts and reveal novel determinants of tail-anchored INM protein targeting.

cell biology↗