Linear ubiquitination triggers Amph-mediated T-tubule biogenesis

Sep 30, 2026

Transverse tubules (T-tubules) are essential muscle membrane invaginations that enable rapid, synchronized excitation–contraction coupling, yet the mechanisms of their formation remain unclear. The study identifies LUBEL/RNF31, an E3 ubiquitin ligase catalyzing linear (M1-linked) ubiquitination, as a key regulator of T-tubule biogenesis in Drosophila. Loss of LUBEL causes Amph-positive membrane sheets instead of tubular networks. LUBEL ubiquitin ligase activity and direct Amph binding drive proper morphology, with conserved Amph–LUBEL interactions facilitating membrane tubulation.

LanguageEnglish

CategoryHealthcare

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Pages16

Reading Time40 min

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Introduction

T-tubules in excitation–contraction coupling

Known regulators and related myopathies

Amph2 as a BAR domain protein and caveolin-dependent mechanisms

CELL BIOLOGY Linear ubiquitination triggers Amph-mediated T-tubule biogenesis Kohei Kawaguchi1, Yutaro Hama2, Harunori Yoshikawa3, Kohei Nishino3, Kazuki Morimoto4, Tsuyoshi Nakamura1, Michiko Koizumi1, Yuriko Sakamaki5, Kota Abe6, Soichiro Kakuta7, Koichiro Ichimura8, Fumiyo Ikeda9, Hidetaka Kosako3, Naonobu Fujita1,4* Transverse tubules (T-tubules) are invaginations of the muscle plasma membrane that facilitate rapid transmission of action potentials, ensuring synchronized muscle contraction. Despite their essential role in muscle physiology, the mechanisms underlying T-tubule formation remain elusive. Here, we identify LUBEL/RNF31, a ubiquitin E3 ligase responsible for linear (M1-linked) ubiquitination, as a key regulator ofT-tubule biogenesis in Drosophila. Loss of LUBEL leads to Amphiphysin (Amph)–positive membrane sheets instead of tubular networks. The ubiquitin ligase activity of LUBELand direct interaction withAmph, a BAR domain protein involved in membrane tubulation, are crucial for proper T-tubule morphology. LUBEL and M1-linked ubiquitin chains assemble into puncta on membranes through multivalent interactions, facilitating Amph-mediated tubulation. Notably, the Amph-LUBEL/ RNF31 interaction is evolutionarily conserved across species, underscoring a fundamental role for linear ubiquitination in membrane remodeling. Our findings uncover an unexpected function of linear ubiquitination in membrane deformation driven by BAR proteins. copyright © 2026 the Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. no claim to original U.S. Government Works. distributed under a creative commons Attribution license 4.0 (cc BY) . INTRODUCTION Transverse tubules (T-tubules) are specialized plasma membrane invaginations that form a unique tubular network in muscle cells (1) . During excitation-contraction coupling, a stimulus from motor neurons triggers depolarization ofsarcolemma, the plasma membrane in muscle cells. This depolarization propagates through the T-tubules, ensuring the rapid and synchronized transmission of signals to thesarcoplasmic reticulum (SR), which releases calcium ions into the cytosol, ultimately driving muscle contraction and movement. Defects in T-tubule organization are linked to various congenital mus cular diseases, underscoring their physiological significance. Many key regulators of T-tubule shaping have been identified as causative genes of congenital myopathies (2). Centronuclear myopathy (CNM), a severe congenital myopathy characterized by T-tubule defects and muscle weakness, is associated with mutations in three membrane trafficking-related genes: BIN1 (Bridging Integrator-1; also known as Amphiphysin 2, Amph2), DNM2 (Dynamin 2), and MTM1 (Myotubularin 1) (2). Amph2 is a BAR domain protein that induces membrane tubulation (3–6). Its N-terminal BAR domain forms banana-shaped dimers that interact with negatively charged phospholipids via their positively charged concave surfaces. These dimers further assemble into extensive networks, promoting membrane curvature and tubulation 1cell Biology center, institute of integrated Research, institute of Science tokyo, 4259 S2-11 nagatsuta, Midori-ku, Yokohama 226-8501, Japan. 2institute for Genetic Medicine, hokkaido University, Sapporo 060-0815, Japan. 3division of cell Signaling, Fujii Memorial institute of Medical Sciences, institute of Advanced Medical Sciences, tokushima University, tokushima 770-8503, Japan. 4Graduate School of life Science and technology, institute of Science tokyo, Yokohama 226-8501, Japan. 5Ochanomizu Research Facility (ORF), Bioscience center, Research infrastructure Management center, institute of Science tokyo, tokyo 113-8510, Japan. 6department of homeostatic Regulation, division of cellular and Molecular Biology, Research institute for Microbial diseases, the University of Osaka, Suita 565-0871, Japan. 7laboratory of Morphology and image Analysis, Biomedica

FAQs

What role do T-tubules play in muscle physiology?

T-tubules are plasma membrane invaginations that propagate depolarization during excitation–contraction coupling, ensuring rapid and synchronized signaling to the sarcoplasmic reticulum for calcium release and muscle contraction.

What does this study identify as a key regulator of T-tubule formation?

It identifies LUBEL/RNF31 as a ubiquitin E3 ligase that performs linear (M1-linked) ubiquitination and regulates T-tubule biogenesis in Drosophila.

How does loss of LUBEL affect membrane structures in Drosophila muscles?

Loss of LUBEL leads to Amphiphysin (Amph)-positive membrane sheets rather than tubular networks, indicating a requirement for linear ubiquitination in proper tubule morphology.

Sep 30, 2026

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