Athena Vale
Myogenic muscle is a term that refers to the process of myogenesis, which is the formation and development of muscular tissue from undifferentiated cells. This process is highly complex and involves the development of multinucleate muscle cells from cell lineages that are mesodermal in origin. Myogenesis is regulated by multiple factors, including MyoD, Myf5, Myogenin, and MRF-4, and is essential for the formation of muscles that enable movement and breathing. The myogenic mechanism also refers to how arteries and arterioles react to changes in blood pressure to maintain a constant blood flow, which is known as the Bayliss effect.
| Characteristics | Values |
|---|---|
| Definition | The myogenic mechanism is how arteries and arterioles react to an increase or decrease of blood pressure to keep the blood flow constant within the blood vessel. |
| Myogenic response | A contraction initiated by the myocyte itself instead of an outside occurrence or stimulus such as nerve innervation. |
| Myogenic tone | The 'basal' myogenic tone may be useful in the regulation of organ blood flow and peripheral resistance, as it positions a vessel in a preconstricted state that allows other factors to induce additional constriction or dilation to increase or decrease blood flow. |
| Myogenic mechanism in the kidney | Myogenic mechanisms in the kidney are part of the autoregulation mechanism which maintains a constant renal blood flow at varying arterial pressure. |
| Bayliss effect or Bayliss myogenic response | A special manifestation of the myogenic tone in the vasculature. The Bayliss effect in vascular smooth muscle cells is a response to stretch. |
| Myogenic muscle composition | Skeletal muscle comprises different muscle fibers, including slow- and fast-type muscles, and satellite cells (SCs), which exist in individual muscle fibers and possess different myogenic properties. |
| Myogenesis | Myogenesis is the process of formation of the muscles that enable movement and breathing. |
| Myogenesis process | Myogenesis is a multistep process that refers to the formation and development of muscular tissue from undifferentiated cells. |
| Myogenesis cell lineages | Muscle cells come from two cell lineages in the somite. |
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What You'll Learn
Myogenesis is the complex process of muscle development
During myogenesis, muscle fibres form through the fusion of precursor myoblasts, creating multinucleated fibres known as myotubes. Myoblasts are muscle progenitor cells that can either proliferate or differentiate into myotubes. This decision is influenced by the presence of growth factors, specifically fibroblast growth factor (FGF). When FGF is abundant, myoblasts proliferate, but when it is depleted, they cease division and undergo differentiation.
The differentiation process occurs in stages. Initially, myoblasts exit the cell cycle and begin expressing specific genes. Subsequently, they align with each other, leading to the formation of myotubes. Myotubes can arise through the fusion of multiple mononuclear myoblasts or through mitotic divisions within a single myoblast. In skeletal muscles, the former mechanism is believed to predominate, while in heart muscles, the latter is thought to be more common.
Myogenesis is regulated by various genetic factors, including MyoD, Myf5, Myogenin, and MRF-4. These factors belong to the myogenic bHLH (basic helix-loop-helix) proteins transcription factor family. MyoD and Myf5 play crucial roles in muscle development, and their simultaneous absence results in a complete lack of skeletal muscle formation. PAX3 and c-Met are also important genetic factors, and mutations in PAX3 can disrupt c-Met expression, leading to muscular defects.
The study of myogenesis often relies on in vitro models and cell culture experiments due to the complexity of the process. Recent advancements, such as the use of somitoids (somite-like organoid structures) derived from induced pluripotent stem cells, offer promising tools for investigating the early stages of muscle development and the pathophysiology of muscle-related diseases.
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Myogenic mechanisms help regulate blood flow
Myogenic mechanisms are essential for maintaining blood flow regulation within blood vessels, particularly in response to changes in blood pressure. This process involves the contraction and relaxation of smooth muscle cells in arteries and arterioles, known as the myogenic response or Bayliss effect.
The myogenic response is initiated by the myocyte itself, independent of external stimuli such as nerve innervation. When blood pressure increases, the stretch of the muscle membrane activates stretch-sensitive ion channels, leading to depolarization and muscle contraction. This contraction reduces the lumen's volume, decreasing blood flow through the vessel. The Bayliss effect is particularly relevant in arterioles, where it helps regulate organ blood flow and peripheral resistance by positioning the vessel in a preconstricted state.
Conversely, when the smooth muscle relaxes, the ion channels close, resulting in vasodilation and an increased rate of flow through the lumen. This mechanism is crucial in the kidneys, where it helps maintain a constant glomerular filtration rate despite changes in arterial pressure. The myogenic mechanism contributes to the autoregulation of renal blood flow, ensuring that the filtration process is relatively insensitive to fluctuations in blood pressure.
Myogenic mechanisms are also influenced by the presence of muscle-specific molecules and proteins. For example, myoblasts, which are muscle cell precursors, play a role in muscle regeneration and repair. Additionally, myogenic properties vary between slow- and fast-type muscle fibres, impacting their self-renewal and differentiation capabilities.
In conclusion, myogenic mechanisms are integral to the body's ability to regulate blood flow, particularly in organs like the kidneys, by responding to changes in blood pressure and maintaining a constant flow rate. This complex process involves the interaction of various cellular components and signalling pathways, highlighting the dynamic nature of blood flow regulation in the body.
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Myogenic muscle cells can come from two cell lineages
Myogenic muscle cells are formed through myogenesis, a complex, highly orchestrated process involving the formation and development of muscular tissue from undifferentiated cells. This process is regulated by multiple factors, including MyoD, Myf5, Myogenin, and MRF-4.
During early embryogenesis, the middle germ cell layer of the embryo, the mesoderm, segments into somites. The upper layer of each somite breaks down into myotomes, which release muscular progenitor cells (MPCs). These MPCs differentiate into myocytes, which fuse in response to fibroblast growth factor (FGF) to form primary myotubes.
Myogenic muscle cells can arise from two cell lineages:
Mesodermal Cell Lineage
The mesoderm-derived muscle stem cell lineage is one of the most well-studied aspects of myogenesis. Mesoderm is one of the three germ cell layers of the embryo that segments into somites during early embryogenesis. The upper layer of each somite breaks down into myotomes, which give rise to MPCs or 'embryonic myoblasts'. These myoblasts are committed muscle cell precursors that produce myogenic bHLH (basic helix-loop-helix) proteins, including MyoD and Myf5. The simultaneous presence of MyoD and Myf5 is crucial for the successful development of skeletal muscle. MyoD directly activates its own gene, continuing a cycle of MyoD protein production, while Myf5 expression is regulated by Sonic hedgehog, Wnt1, and MyoD itself.
Satellite Stem Cell Lineage
Satellite stem cells (SatSCs) are another source of myogenic muscle cells. SatSCs are muscle stem cells found between the basal lamina and the sarcolemma (cell membrane) in a quiescent state. Following muscle injury, SatSCs are activated to regenerate damaged myofibers, releasing biomolecules that promote myoblast differentiation into multinucleated myofibers. Studies on Pofut1cax/cax mice have shown that decreased expression of POFUT1 leads to altered post-natal muscle development, with hypertrophy and a reduced number of satellite cells. This suggests that POFUT1 plays a role in Notch-dependent myogenesis, influencing the interaction between the receptor NOTCH and its recombinant DLL1 ligands.
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Myogenic bHLH proteins are powerful transcription factors
Myogenesis is a complex process that involves the formation and development of muscular tissue from undifferentiated cells. It is regulated by multiple factors, including MyoD, Myf5, Myogenin, and MRF-4. MyoD, Myf5, and Myogenin are members of the myogenic bHLH (basic helix-loop-helix) transcription factor family.
The function of myogenic bHLH proteins is dependent on specific amino acids in the basic region, which may influence DNA binding preferences and protein-protein contacts with additional transcription factors. For example, MyoD can bind to motifs with different central dinucleotides, with GA and GG dinucleotides being more associated with neuronal and myogenic genes, respectively. MyoD can also promote chromatin remodelling, making previously hidden E-boxes accessible for binding.
Myogenic bHLH factors are involved in a positive feedback network that maintains the myogenic transcriptional program. CDO, a cell surface receptor, positively regulates myogenesis by activating myogenic bHLH factors through enhanced heterodimer formation. The promyogenic effect of cell-cell contact is linked to the activity of myogenic bHLH factors.
In summary, myogenic bHLH proteins are powerful transcription factors that regulate myogenesis and muscle regeneration. They play a critical role in the development of muscle cells and maintain a positive feedback network that supports the myogenic transcriptional program. The function of these proteins is influenced by specific amino acids and their ability to bind to DNA and interact with other transcription factors.
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Myogenic muscle is composed of different muscle fibres
Myogenic muscle, or skeletal muscle, is composed of different muscle fibres. These fibres are formed from the fusion of developmental myoblasts in a process known as myogenesis, resulting in long multinucleated cells. Myogenesis is a highly complex process that needs to be tightly regulated during development and regeneration, to ensure that the newly formed skeletal muscle is fully functional and integrated with the rest of the organs.
Skeletal muscle fibres can be classified based on two criteria: the speed of their contractions relative to others, and how they regenerate adenosine triphosphate (ATP). Using these criteria, there are three main types of skeletal muscle fibres: slow oxidative (also called slow twitch or Type I), fast oxidative (also called fast twitch or Type IIa), and fast glycolytic (also called fast twitch or Type IIx).
Slow oxidative fibres use aerobic metabolism to produce low-power contractions over long periods and are slow to fatigue. They have a relatively small diameter and thus do not produce a large amount of tension. Fast oxidative fibres also use aerobic metabolism to produce ATP but generate higher-tension contractions than slow oxidative fibres. Fast glycolytic fibres use anaerobic metabolism to produce powerful, high-tension contractions but fatigue quickly.
The different types of muscle fibres can be identified in poultry. For example, the legs and thighs of a turkey are dark meat due to their slow oxidative fibres and robust supply of blood vessels and myoglobin.
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Frequently asked questions
Myogenic muscle refers to the development of muscle or myogenesis.
Myogenesis involves the expression of myogenic regulatory factors and genes such as myocyte enhancer factors, myogenic determination factor (MyoD1), myogenin, and serum response factor.
MyoD is a protein that activates muscle-specific genes and plays a crucial role in the formation of skeletal muscle. It is one of the earliest expressed regulatory factor genes in myogenesis.
Mutations or absence of specific genes, such as PAX3, c-Met, and Myf5, can lead to muscular defects and improper limb muscle development. For example, a lack of c-Met disrupts secondary myogenesis and hinders limb musculature formation.
Understanding myogenic factors and myogenesis has opened up possibilities for converting non-muscle cells into muscle cells. This knowledge can be applied in regenerative medicine and potentially used to repair or enhance muscle tissue.
