Skeletal Muscle: The origin of T-tubules

Ring-like structures made up of caveolae appear to drive the development of membrane invaginations called T-tubules which are important for muscle contraction.
  1. Callum J Quinn
  2. Katharine M Dibb  Is a corresponding author
  1. Unit of Cardiac Physiology, Manchester Academic Health Science Centre, University of Manchester, United Kingdom

In order to move, skeletal muscles connected to the bones of the body must be triggered to contract. This requires nerves in the brain to activate cells within muscle to release calcium ions from their internal store, the sarcoplasmic reticulum. Electrical signals sent from the brain are transmitted to the centre of the muscle cell by invaginations in their plasma membrane, called T-tubules, which are closely associated with the sarcoplasmic reticulum (Franzini-Armstrong, 2018; Smith et al., 2018). This results in the synchronous release of calcium ions throughout the whole cell, ensuring efficient contraction of the muscle.

Mutations in genes that coordinate the development of T-tubules have been associated with debilitating muscle diseases (Fujise et al., 2022). While some of the proteins involved in this process have been identified, such as the membrane shaping protein Bin1, we do not fully understand how T-tubules mature and grow alongside the sarcoplasmic reticulum. Early studies suggest that cave-like pits within the plasma membrane called caveolae – which are found in multiple cell types, including muscle cells – may play a role (Parton and Simons, 2007; Franzini-Armstrong, 1991). However, a lack of appropriate tools has made it difficult for researchers to visualise how this complex process occurs. Now, in eLife, Stéphane Vassilopoulos from Sorbonne Université and colleagues – including Eline Lemerle as first author – report that T-tubules grow from sub-membrane rings composed of caveolae and Bin1 in mammalian skeletal muscle cells (Lemerle et al., 2023).

The team (who are based at multiple institutes in France) studied aggregates of developing human or mouse muscle cells grown in the laboratory, known as myotubes. Using ultrasound, Lemerle et al. removed the upper cell membrane of the myotubes so that the inner side of the plasma membrane could be observed. This revealed rings of plasma membrane closely associated with the sarcoplasmic reticulum, which were coated in the caveolae-forming protein Cav3. A state-of-the-art technique that combines light and electron microscopy (known as CLEM) showed that some of these constructs – which Lemerle et al. termed caveolae rings – had multiple tube-like structures extending from them. Present on the tubular extensions were Bin1 proteins and calcium channels, two components associated with T-tubules, suggesting that these structure may be precursors to T-tubules.

It has been suggested that Bin1 induces membrane curvature and promotes T-tubule development (Lee et al., 2002). By modifying developing muscle cells to contain more of a type of Bin1 protein with a specific lipid-binding domain, Lemerle et al. increased the formation of circular structures – resembling caveolae rings – from which T-tubules could sprout. While all the structures were coated in Bin1, only some were associated with Cav3. Furthermore, when high concentrations of this Bin1 protein were added to a semi-synthetic membrane, the membrane self-assembled into rings and T-tubules similar to those that naturally develop in lab-grown cells. These findings suggest that Bin1 is primarily responsible for organizing the plasma membrane into ring-like platforms which then recruit caveolae and sprout T-tubules (Figure 1).

How T-tubules form in developing muscle cells.

The protein Bin1 (purple) reshapes the plasma membrane to form rings that sit beneath the membrane of the skeletal muscle cell. Cave-like pits in the plasma membrane called caveolae (blue) are then recruited to the ring together with the caveolae-forming protein Cav3 (yellow). This results in structures termed caveolae rings which associate with the sarcoplasmic reticulum (SR) at the sites where caveolae are not present. Cav3 proteins and caveolae then accumulate at specific locations on the ring and tube-like structures start to emerge from these sites. As the tubule matures, calcium channels called dihydropyridine receptors (DHPRs; blue) begin to form a calcium release unit with ryanodine receptor 1 (RyR1; green) on the membrane of the sarcoplasmic reticulum. This interaction resembles how T-tubules and the sarcoplasmic reticulum associate with one another in mature skeletal muscle cells.

Next, Lemerle et al. reduced the amount of Cav3 expressed in the myotubes to better understand the role caveolae play in T-tubule formation. This resulted in smaller rings and a dramatic decrease in tubulation, suggesting that caveolae are important for this process. The team then analysed developing muscle cells that had been genetically modified to contain mutations in the gene for Cav3 which are known to cause human muscle diseases called caveolinopathies (Woodman et al., 2004). As expected, this resulted in aberrations in how caveolae were organized and disrupted tubulation in the mutant muscle cells, which correlated with the mature T-tubule malformations observed in tissue extracts from patients with caveolinopathies.

In this breakthrough study, Lemerle et al. have presented a compelling new mechanism for how T-tubules develop. In addition to making a significant contribution to skeletal muscle research, these findings likely relate to cardiac muscle cells which also require Bin1 and Cav3, amongst other proteins, to form T-tubules (Caldwell et al., 2014; Bryant et al., 2018). Faults in cardiac T-tubules have been associated with heart failure, arrhythmias, and other cardiac diseases (Smith et al., 2018; Smith et al., 2022). Therefore, the findings and experimental approach used by Lemerle et al. could help researchers better understand how T-tubules can be targeted to treat muscle diseases that impact the heart as well as those associated with movement.


Article and author information

Author details

  1. Callum J Quinn

    Callum J Quinn is in the Unit of Cardiac Physiology, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-1713-5975
  2. Katharine M Dibb

    Katharine M Dibb is in the Unit of Cardiac Physiology, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom

    For correspondence
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9309-3853

Publication history

  1. Version of Record published: June 20, 2023 (version 1)


© 2023, Quinn and Dibb

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.


  • 1,027
    Page views
  • 26
  • 0

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Callum J Quinn
  2. Katharine M Dibb
Skeletal Muscle: The origin of T-tubules
eLife 12:e88954.
  1. Further reading

Further reading

    1. Cell Biology
    2. Medicine
    Chun Wang, Khushpreet Kaur ... Gabriel Mbalaviele
    Research Article

    Chemotherapy is a widely used treatment for a variety of solid and hematological malignancies. Despite its success in improving the survival rate of cancer patients, chemotherapy causes significant toxicity to multiple organs, including the skeleton, but the underlying mechanisms have yet to be elucidated. Using tumor-free mouse models, which are commonly used to assess direct off-target effects of anti-neoplastic therapies, we found that doxorubicin caused massive bone loss in wild-type mice, a phenotype associated with increased number of osteoclasts, leukopenia, elevated serum levels of danger-associated molecular patterns (DAMPs; e.g. cell-free DNA and ATP) and cytokines (e.g. IL-1β and IL-18). Accordingly, doxorubicin activated the absent in melanoma (AIM2) and NLR family pyrin domain containing 3 (NLRP3) inflammasomes in macrophages and neutrophils, causing inflammatory cell death pyroptosis and NETosis, which correlated with its leukopenic effects. Moreover, the effects of this chemotherapeutic agent on cytokine secretion, cell demise, and bone loss were attenuated to various extent in conditions of AIM2 and/or NLRP3 insufficiency. Thus, we found that inflammasomes are key players in bone loss caused by doxorubicin, a finding that may inspire the development of a tailored adjuvant therapy that preserves the quality of this tissue in patients treated with this class of drugs.

    1. Cell Biology
    Zeina Salloum, Kristin Dauner ... Xiaohui Zha
    Research Article

    Stains are known to be anti-inflammatory, but the mechanism remains poorly understood. Here we show that macrophages, either treated with statin in vitro or from statin-treated mice, have reduced cholesterol levels and higher expression of Jmjd3, a H3K27me3 demethylase. We provide evidence that lowering cholesterol levels in macrophages suppresses the ATP synthase in the inner mitochondrial membrane (IMM) and changes the proton gradient in the mitochondria. This activates NFkB and Jmjd3 expression to remove the repressive marker H3K27me3. Accordingly, the epigenome is altered by the cholesterol reduction. When subsequently challenged by the inflammatory stimulus LPS (M1), both macrophages treated with statins in vitro or isolated from statin-treated mice in vivo, express lower levels pro-inflammatory cytokines than controls, while augmenting anti-inflammatory Il10 expression. On the other hand, when macrophages are alternatively activated by IL4 (M2), statins promote the expression of Arg1, Ym1, and Mrc1. The enhanced expression is correlated with the statin-induced removal of H3K27me3 from these genes prior to activation. In addition, Jmjd3 and its demethylase activity are necessary for cholesterol to modulate both M1 and M2 activation. We conclude that upregulation of Jmjd3 is a key event for the anti-inflammatory function of statins on macrophages.