scholarly journals Genetic screen in Drosophila muscle identifies autophagy-mediated T-tubule remodeling and a Rab2 role in autophagy

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Naonobu Fujita ◽  
Wilson Huang ◽  
Tzu-han Lin ◽  
Jean-Francois Groulx ◽  
Steve Jean ◽  
...  
Keyword(s):  
Essential Role ◽  
Abdominal Muscles ◽  
Genetic Screens ◽  
Developmentally Regulated ◽  
Direct Role ◽  
Contraction Coupling ◽  
Membrane Flux ◽  
Contractile System ◽  
T Tubules ◽  
Muscle Remodeling

Transverse (T)-tubules make-up a specialized network of tubulated muscle cell membranes involved in excitation-contraction coupling for power of contraction. Little is known about how T-tubules maintain highly organized structures and contacts throughout the contractile system despite the ongoing muscle remodeling that occurs with muscle atrophy, damage and aging. We uncovered an essential role for autophagy in T-tubule remodeling with genetic screens of a developmentally regulated remodeling program in Drosophila abdominal muscles. Here, we show that autophagy is both upregulated with and required for progression through T-tubule disassembly stages. Along with known mediators of autophagosome-lysosome fusion, our screens uncovered an unexpected shared role for Rab2 with a broadly conserved function in autophagic clearance. Rab2 localizes to autophagosomes and binds to HOPS complex members, suggesting a direct role in autophagosome tethering/fusion. Together, the high membrane flux with muscle remodeling permits unprecedented analysis both of T-tubule dynamics and fundamental trafficking mechanisms.

scholarly journals RNA polymerase II plays an active role in the formation of gene loops through the Rpb4 subunit

2019 ◽  
Vol 47 (17) ◽  
pp. 8975-8987 ◽  
Author(s):  
Paula Allepuz-Fuster ◽  
Michael J O’Brien ◽  
Noelia González-Polo ◽  
Bianca Pereira ◽  
Zuzer Dhoondia ◽  
...  
Keyword(s):  
Rna Polymerase ◽  
Rna Polymerase Ii ◽  
Essential Role ◽  
Transcription Termination ◽  
Active Role ◽  
The Other ◽  
Loop Formation ◽  
Direct Role

AbstractGene loops are formed by the interaction of initiation and termination factors occupying the distal ends of a gene during transcription. RNAPII is believed to affect gene looping indirectly owing to its essential role in transcription. The results presented here, however, demonstrate a direct role of RNAPII in gene looping through the Rpb4 subunit. 3C analysis revealed that gene looping is abolished in the rpb4Δ mutant. In contrast to the other looping-defective mutants, rpb4Δ cells do not exhibit a transcription termination defect. RPB4 overexpression, however, rescued the transcription termination and gene looping defect of sua7-1, a mutant of TFIIB. Furthermore, RPB4 overexpression rescued the ssu72-2 gene looping defect, while SSU72 overexpression restored the formation of gene loops in rpb4Δ cells. Interestingly, the interaction of TFIIB with Ssu72 is compromised in rpb4Δ cells. These results suggest that the TFIIB–Ssu72 interaction, which is critical for gene loop formation, is facilitated by Rpb4. We propose that Rpb4 is promoting the transfer of RNAPII from the terminator to the promoter for reinitiation of transcription through TFIIB–Ssu72 mediated gene looping.

scholarly journals Mechanotransduction and Metabolism in Cardiomyocyte Microdomains

2016 ◽  
Vol 2016 ◽  
pp. 1-17 ◽  
Author(s):  
Francesco S. Pasqualini ◽  
Alexander P. Nesmith ◽  
Renita E. Horton ◽  
Sean P. Sheehy ◽  
Kevin Kit Parker
Keyword(s):  
Posttranslational Modifications ◽  
Energy Production ◽  
Cytoskeletal Proteins ◽  
Hierarchical Organization ◽  
Energy Utilization ◽  
Emergent Properties ◽  
Cardiac Diseases ◽  
Contraction Coupling ◽  
T Tubules ◽  
The Impact

Efficient contractions of the left ventricle are ensured by the continuous transfer of adenosine triphosphate (ATP) from energy production sites, the mitochondria, to energy utilization sites, such as ionic pumps and the force-generating sarcomeres. To minimize the impact of intracellular ATP trafficking, sarcomeres and mitochondria are closely packed together and in proximity with other ultrastructures involved in excitation-contraction coupling, such as t-tubules and sarcoplasmic reticulum junctions. This complex microdomain has been referred to as the intracellular energetic unit. Here, we review the literature in support of the notion that cardiac homeostasis and disease are emergent properties of the hierarchical organization of these units. Specifically, we will focus on pathological alterations of this microdomain that result in cardiac diseases through energy imbalance and posttranslational modifications of the cytoskeletal proteins involved in mechanosensing and transduction.

Excitation–contraction coupling in crab muscle fibers with swollen T tubules

1985 ◽  
Vol 63 (7) ◽  
pp. 879-885 ◽  
Author(s):  
J. H. Leal-Cardoso ◽  
G. Suarez-Kurtz
Keyword(s):  
Time Course ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Membrane Excitability ◽  
High Potassium ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Voltage Dependent ◽  
T Tubules

Single crab (Callinectes danae) fibers were equilibrated with isotonic, high KC1 solutions and were subsequently returned to the control saline. This caused marked swelling of the T tubules. Fibers treated with 100 mM KCl had a 2.5-mV residual depolarization, a 50% decrease in effective membrane resistance (Reff) and a 75% reduction in membrane time constant (τm). These fibers exhibited large increases in membrane conductance upon depolarization and were inexcitable; membrane depolarization with current pulses elicited no contraction. The effects of the KCl treatment on membrane properties were not reproduced by treatment with high potassium gluconate solutions, which did not cause tubular swelling. Tetrabutylammonium (10 mM) or Ba ions (10–20 mM), but not tetraethylammonium (40–100 mM), Sr ions (15–70 mM), or procaine (1–8 mM) reversed the effects of the KCl treatment on Reff, τm, membrane excitability, and excitation–contraction coupling. The time course of the Ba effects was consistent with the suggestion that the KCl treatment increases the K conductance of the tubular membranes, which in turn prevents the activation of voltage-dependent Ca channels located in the membranes of the T system. This results in inhibition of the Ca-dependent electrogenesis and consequently, the absence of contraction upon depolarization of the plasma membrane.

Evidence for an essential role for calcium in excitation-contraction coupling in skeletal muscle

1964 ◽  
Vol 160 (981) ◽  
pp. 504-512 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibre ◽  
Calcium Ions ◽  
Essential Role ◽  
Mechanical Response ◽  
Frog Heart ◽  
Muscle Fibres ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Spontaneous Action

The events and processes that link the electrical events which occur at the surface of a muscle fibre with the contractile process that takes place within the fibre, have been a continuing source of interest. Recently attention has been concentrated on the role played by calcium ions in linking these two events. As often happens in physiological investigations, the idea that calcium ions play an essential role in excitation-contraction coupling is not new. As long ago as 1883 Ringer demonstrated that the frog heart fails to contract and remains relaxed when calcium ions are absent from its perfusion fluid. Later it was shown that under this condition the rhythmic spontaneous action potentials of this preparation are still present in an only slightly modified form (Mines 1913). It was known at that time that the depolarization of the muscle fibre membrane is the electrical event responsible for initiating the mechanical response (Biedermann 1896) and although this point has been disputed from time to time, the evidence presently available makes it obvious that this is the case. One explanation of these observations is that the action potential or depolarization permits or promotes the movement of calcium ions from the surface to the interior of the muscle fibre and that these ions then initiate the mechanical response. A working hypothesis of this type was proposed by Sandow (1952). However, until fairly recently the only direct evidence supporting such an hypothesis was the demonstration by Heilbrunn & Wiercinski (1947) that calcium was the only physiologically occurring cation which would cause shortening when injected into bits of skeletal muscle fibres in low concentrations. This effect was later confirmed under more physiological conditions by Niedergerke (1955). Although there is considerable evidence of recent origin showing that calcium ions play an essential role in coupling in smooth and cardiac muscles, for the sake of brevity attention will be concentrated on skeletal muscle in the present discussion.

scholarly journals Pachymic Acid Attenuated Doxorubicin-Induced Heart Failure by Suppressing miR-24 and Preserving Cardiac Junctophilin-2 in Rats

2021 ◽  
Vol 22 (19) ◽  
pp. 10710
Author(s):  
Nahla N. Younis ◽  
Alaa Salama ◽  
Mohamed A. Shaheen ◽  
Rana G. Eissa
Keyword(s):  
Electron Microscopy ◽  
Heart Failure ◽  
Fiber Diameter ◽  
Ryanodine Receptors ◽  
Cardiac Contractility ◽  
Histological Assessment ◽  
Contraction Coupling ◽  
Pachymic Acid ◽  
T Tubules ◽  
Mitochondrial Number

Defects in cardiac contractility and heart failure (HF) are common following doxorubicin (DOX) administration. Different miRs play a role in HF, and their targeting was suggested as a promising therapy. We aimed to target miR-24, a suppressor upstream of junctophilin-2 (JP-2), which is required to affix the sarcoplasmic reticulum to T-tubules, and hence the release of Ca2+ in excitation–contraction coupling using pachymic acid (PA) and/or losartan (LN). HF was induced with DOX (3.5 mg/kg, i.p six doses, twice weekly) in 24 rats. PA and LN (10 mg/kg, daily) were administered orally for four weeks starting the next day of the last DOX dose. Echocardiography, left ventricle (LV) biochemical and histological assessment and electron microscopy were conducted. DOX increased serum BNP, HW/TL, HW/BW, mitochondrial number/size and LV expression of miR-24 but decreased EF, cardiomyocyte fiber diameter, LV content of JP-2 and ryanodine receptors-2 (RyR2). Treatment with either PA or LN reversed these changes. Combined PA + LN attained better results than monotherapies. In conclusion, HF progression following DOX administration can be prevented or even delayed by targeting miR-24 and its downstream JP-2. Our results, therefore, suggest the possibility of using PA alone or as an adjuvant therapy with LN to attain better management of HF patients, especially those who developed tolerance toward LN.

scholarly journals Modelling depolarization delay, sodium currents, and electrical potentials in cardiac transverse tubules

2019 ◽  
Author(s):  
Sarah H. Vermij ◽  
Hugues Abriel ◽  
Jan P. Kucera
Keyword(s):  
Striated Muscle ◽  
Sodium Current ◽  
Cardiac Cells ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Tubular Membrane ◽  
Electrical Potentials ◽  
Tubular Lumen ◽  
T Tubules ◽  
Extracellular Potentials

ABSTRACTT-tubules are invaginations of the lateral membrane of striated muscle cells that provide a large surface for ion channels and signaling proteins, thereby supporting excitation-contraction coupling. T-tubules are often remodeled in heart failure. To better understand the electrical behavior of T-tubules of cardiac cells in health and disease, this study addresses two largely unanswered questions regarding their electrical properties: (1) the delay of T-tubular membrane depolarization and (2) the effects of T-tubular sodium current on T-tubular potentials.Here, we present an elementary computational model to determine the delay in depolarization of deep T-tubular membrane segments as the narrow T-tubular lumen provides resistance against the extracellular current. We compare healthy tubules to tubules with constrictions and diseased tubules from mouse and human, and conclude that constrictions greatly delay T-tubular depolarization, and diseased T-tubules depolarize faster than healthy ones due to tubule widening. We moreover model the effect of T-tubular sodium current on intraluminal T-tubular potentials. We observe that extracellular potentials become negative during the sodium current transient (up to −50 mV in constricted T-tubules), which feedbacks on sodium channel function (self-attenuation) in a manner resembling ephaptic effects that have been described for intercalated discs where opposing membranes are very close together.These results show that (1) the excitation-contraction coupling defects seen in diseased cells cannot be explained by T-tubular remodeling alone; and (2) the sodium current may modulate intraluminal potentials. Such extracellular potentials might also affect excitation-contraction coupling.

scholarly journals An autophagy-dependent tubular lysosomal network synchronizes degradative activity required for muscle remodeling

2020 ◽  
Vol 133 (21) ◽  
pp. jcs248336
Author(s):  
Tadayoshi Murakawa ◽  
Amy A. Kiger ◽  
Yuriko Sakamaki ◽  
Mitsunori Fukuda ◽  
Naonobu Fujita
Keyword(s):  
Abdominal Muscle ◽  
Autophagic Flux ◽  
Snare Protein ◽  
Developmentally Regulated ◽  
Limited Knowledge ◽  
Muscle Remodeling ◽  
Broad Region

ABSTRACTLysosomes are compartments for the degradation of both endocytic and autophagic cargoes. The shape of lysosomes changes with cellular degradative demands; however, there is limited knowledge about the mechanisms or significance that underlies distinct lysosomal morphologies. Here, we found an extensive tubular autolysosomal network in Drosophila abdominal muscle remodeling during metamorphosis. The tubular network transiently appeared and exhibited the capacity to degrade autophagic cargoes. The tubular autolysosomal network was uniquely marked by the autophagic SNARE protein Syntaxin17 and its formation depended on both autophagic flux and degradative function, with the exception of the Atg12 and Atg8 ubiquitin-like conjugation systems. Among ATG-deficient mutants, the efficiency of lysosomal tubulation correlated with the phenotypic severity in muscle remodeling. The lumen of the tubular network was continuous and homogeneous across a broad region of the remodeling muscle. Altogether, we revealed that the dynamic expansion of a tubular autolysosomal network synchronizes the abundant degradative activity required for developmentally regulated muscle remodeling.

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