Troponin T (TnT) is a central player in the calcium regulation of actin thin filament function and is essential for the contraction of striated muscles. Three homologous genes have evolved in ...vertebrates to encode three muscle type-specific TnT isoforms: TNNT1 for slow skeletal muscle TnT, TNNT2 for cardiac muscle TnT, and TNNT3 for fast skeletal muscle TnT. Alternative splicing and posttranslational modifications confer additional structural and functional variations of TnT during development and muscle adaptation to various physiological and pathological conditions. This review focuses on the TnT isoform genes and their molecular evolution, alternative splicing, developmental regulation, structure–function relationships of TnT proteins, posttranslational modifications, and myopathic mutations and abnormal splicing. The goal is to provide a concise summary of the current knowledge and some perspectives for future research and translational applications.
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•Troponin T (TnT) is a regulator of striated muscle contraction.•3 Homologous genes have evolved in vertebrates encoding muscle type TnT isoforms.•Alternative splicing and posttranslational modifications add variations of TnT.•TnT gene expression is regulated during development and adaptations.•This review summarizes the current knowledge and perspectives of TnT research.
Calponin is an actin filament-associated regulatory protein expressed in smooth muscle and many types of non-muscle cells. Three homologous genes, CNN1, CNN2 and CNN3, encoding calponin isoforms 1, ...2, and 3, respectively, are present in vertebrate species. All three calponin isoforms are actin-binding proteins with functions in inhibiting actin-activated myosin ATPase and stabilizing the actin cytoskeleton, while each isoform executes different physiological roles based on their cell type-specific expressions. Calponin 1 is specifically expressed in smooth muscle cells and plays a role in fine-tuning smooth muscle contractility. Calponin 2 is expressed in both smooth muscle and non-muscle cells and regulates multiple actin cytoskeleton-based functions. Calponin 3 participates in actin cytoskeleton-based activities in embryonic development and myogenesis. Phosphorylation has been extensively studied for the regulation of calponin functions. Cytoskeleton tension regulates the transcription of CNN2 gene and the degradation of calponin 2 protein. This review summarizes our knowledge learned from studies over the past three decades, focusing on the evolutionary lineage of calponin isoform genes, their tissue- and cell type-specific expressions, structure–function relationships, and mechanoregulation.
Superhydrophobic and superoleophobic surfaces have so far been made by roughening a hydrophobic material. However, no surfaces were able to repel extremely-low-energy liquids such as fluorinated ...solvents, which completely wet even the most hydrophobic material. We show how roughness alone, if made of a specific doubly reentrant structure that enables very low liquid-solid contact fraction, can render the surface of any material superrepellent. Starting from a completely wettable material (silica), we micro- and nanostructure its surface to make it superomniphobic and bounce off all available liquids, including perfluorohexane. The same superomniphobicity is further confirmed with identical surfaces of a metal and a polymer. Free of any hydrophobic coating, the superomniphobic silica surface also withstands temperatures over 1000°C and resists biofouling.
The effects of Al on microstructure, stacking fault energy, tensile properties and fractured surface in Fe–18Mn–0.6C–(0–2)Al twinning-induced plasticity (TWIP) steels were systemically investigated. ...The Al addition suppressed the cementite precipitation during cooling after hot-rolling. The stacking-fault energy was linearly raised with a constant slope of 7.8mJm−2 per 1 wt.% Al. The Al addition increased the yield stress, reduction in area, uniform (eu), and post-uniform (epu) elongations, while it decreased the amount and rate of strain hardening and dynamic strain aging (DSA). In particular, although the epu of the TWIP steel without Al was almost zero, it was improved up to ∼7% by addition of 2 wt.% Al, which was comparable with those of dual phase and TRIP steels with a similar tensile strength of 780MPa. In order to elucidate the reasons for the poor epu in C-bearing TWIP steel and for the prolonged epu by Al addition, the apparent absolute strain-rate sensitivity m=dσ/dlnε˙ of two TWIP steels with different Al concentrations of 0 and 2 wt.% was investigated at room temperature. Both TWIP steels had negative strain-rate sensitivity at a large strain (ε=0.4) of just before necking. However, the Al addition increased the strain-rate sensitivity, resulting in improved epu because of reduced DSA by decreases in both activity and diffusivity of C in austenite.
Checkpoint receptor blockers, known to act by blocking the pathways that inhibit immune cell activation and stimulate immune responses against tumor cells, have been immensely successful in the ...treatment of cancer. Among several checkpoint receptors of immune cells, cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), programmed cell death protein-1 (PD-1), T-cell immunoglobulin and ITIM domain (TIGIT), T-cell immunoglobulin-3 (TIM-3) and lymphocyte activation gene 3 (LAG-3) are the most commonly targeted checkpoints for cancer immunotherapy. Six drugs including one CTLA-4 blocker (ipilimumab), two PD-1 blockers (nivolumab and pembrolizumab) and three PD-L1 blockers (atezolizumab, avelumab and durvalumab) are approved for the treatment of different types of cancers including both solid tumors such as melanoma, lung cancer, head and neck cancer, bladder cancer and Merkel cell cancer as well as hematological tumors such as classic Hodgkin's lymphoma. The main problem with checkpoint blockers is that only a fraction of patients respond to the therapy. Insufficient immune activation is considered as one of the main reason for low response rates and combination of checkpoint blockers has been proposed to increase the response rates. The combination of checkpoint blockers was successful in melanoma but had significant adverse events. A combination that is selected based on the mechanistic differences between checkpoints and the differences in expression of checkpoints and their ligands in the tumor microenvironment could have a synergistic effect in a given cancer subtype and also have a manageable safety profile. This review aims to help in design of optimal checkpoint blocker combinations by discussing the mechanistic details and outlining the subtle differences between major checkpoints targeted for cancer immunotherapy.
The ability to manipulate droplets on a substrate using electric signals
-known as digital microfluidics-is used in optical
, biomedical
, thermal
and electronic
applications and has led to ...commercially available liquid lenses
and diagnostics kits
. Such electrical actuation is mainly achieved by electrowetting, with droplets attracted towards and spreading on a conductive substrate in response to an applied voltage. To ensure strong and practical actuation, the substrate is covered with a dielectric layer and a hydrophobic topcoat for electrowetting-on-dielectric (EWOD)
; this increases the actuation voltage (to about 100 volts) and can compromise reliability owing to dielectric breakdown
, electric charging
and biofouling
. Here we demonstrate droplet manipulation that uses electrical signals to induce the liquid to dewet, rather than wet, a hydrophilic conductive substrate without the need for added layers. In this electrodewetting mechanism, which is phenomenologically opposite to electrowetting, the liquid-substrate interaction is not controlled directly by electric field but instead by field-induced attachment and detachment of ionic surfactants to the substrate. We show that this actuation mechanism can perform all the basic fluidic operations of digital microfluidics using water on doped silicon wafers in air, with only ±2.5 volts of driving voltage, a few microamperes of current and about 0.015 times the critical micelle concentration of an ionic surfactant. The system can also handle common buffers and organic solvents, promising a simple and reliable microfluidic platform for a broad range of applications.
The emergence of electrowetting-on-dielectric (EWOD) in the early 2000s made the once-obscure electrowetting phenomenon practical and led to numerous activities over the last two decades. As an ...eloquent microscale liquid handling technology that gave birth to digital microfluidics, EWOD has served as the basis for many commercial products over two major application areas: optical, such as liquid lenses and reflective displays, and biomedical, such as DNA library preparation and molecular diagnostics. A number of research or start-up companies (
e.g.
, Phillips Research, Varioptic, Liquavista, and Advanced Liquid Logic) led the early commercialization efforts and eventually attracted major companies from various industry sectors (
e.g.
, Corning, Amazon, and Illumina). Although not all of the pioneering products became an instant success, the persistent growth of liquid lenses and the recent FDA approvals of biomedical analyzers proved that EWOD is a powerful tool that deserves a wider recognition and more aggressive exploration. This review presents the history around major EWOD products that hit the market to show their winding paths to commercialization and summarizes the current state of product development to peek into the future. In providing the readers with a big picture of commercializing EWOD and digital microfluidics technology, our goal is to inspire further research exploration and new entrepreneurial adventures.
Electrowetting on EWOD surface: a droplet beading or spreading (left) or translating (right) by electric signals. The EWOD technology made the once-obscure electrowetting phenomenon practical, leading to the host of commercial products today.
The powered flight of animals requires efficient and sustainable contractions of the wing muscles of various flying species. Despite their high degree of phylogenetic divergence, flight muscles in ...insects and vertebrates are striated muscles with similarly specialized sarcomeric structure and basic mechanisms of contraction and relaxation. Comparative studies examining flight muscles together with other striated muscles can provide valuable insights into the fundamental mechanisms of muscle contraction and energetic efficiency. Here, we conducted a literature review and data mining to investigate the independent emergence and evolution of flight muscles in insects, birds, and bats, and the likely molecular basis of their contractile features and energetic efficiency. Bird and bat flight muscles have different metabolic rates that reflect differences in energetic efficiencies while having similar contractile machinery that is under the selection of similar natural environments. The significantly lower efficiency of insect flight muscles along with minimized energy expenditure in Ca
handling is discussed as a potential mechanism to increase the efficiency of mammalian striated muscles. A better understanding of the molecular evolution of myofilament proteins in the context of physiological functions of invertebrate and vertebrate flight muscles can help explore novel approaches to enhance the performance and efficiency of skeletal and cardiac muscles for the improvement of human health.
Troponin T (TnT) is the thin filament anchoring subunit of troponin complex and plays an organizer role in the Ca
2+
-regulation of striated muscle contraction. From an ancestral gene emerged ~ 700 ...million years ago in Bilateria, three homologous genes have evolved in vertebrates to encode muscle type-specific isoforms of TnT. Alternative splicing variants of TnT are present in vertebrate and invertebrate muscles to add functional diversity. While the C-terminal region of TnT is largely conserved, it contains an alternatively spliced segment emerged early in
C. elegans
, which has evolved into a pair of mutually exclusive exons in arthropods (10A and 10B of
Drosophila TpnT
gene) and vertebrates (16 and 17 of fast skeletal muscle
Tnnt3
gene). The C-terminal alternatively spliced segment of TnT interfaces with the other two subunits of troponin with functional significance. The vertebrate cardiac TnT gene that emerged from duplication of the fast TnT gene has eliminated this alternative splicing by the fixation of an exon 17-like constitutive exon, indicating a functional value in slower and rhythmic contractions. The vertebrate slow skeletal muscle TnT gene that emerged from duplication of the cardiac TnT gene has the exon 17-like structure conserved, indicating its further function in sustained and fatigue resistant contractions. This functionality-based evolution is consistent with the finding that exon 10B-encoded segment of
Drosophila
TnT homologous to the exon 17-encoded segment of vertebrate fast TnT is selectively expressed in insect heart and leg muscles. The evolution of the C-terminal variable region of TnT demonstrates a submolecular mechanism in modifying striated muscle contractility and for the treatment of muscle and heart diseases.
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