Dominic Stone
Zebrafish have been used as a model system for investigating muscle patterning and growth due to their simple axial musculature with distinct fibre types. Axial muscle is the most abundant tissue type in the body of fishes and is responsible for producing undulatory locomotion. In larval zebrafish, axial muscle fibres follow helical trajectories that taper towards the tail. Under the skin, a thin layer of red muscle fibres covers the fast axial muscle fibres. The development of axial musculature (primary myogenesis) occurs within the paraxial mesoderm, which segments along the anteroposterior axis to form blocks of cells called somites. Zebrafish larvae muscles can be examined in vitro using mechanical and x-ray methods, revealing a significant fast contractile component.
| Characteristics | Values |
|---|---|
| Axial muscle fibre orientations | In larval zebrafish, axial muscle fibres follow helical trajectories that taper towards the tail |
| Axial muscle fibre trajectory | Follows the local muscle-fibre direction and spans a longitudinal series of myomeres |
| Muscle architecture analysis | High-resolution confocal laser microscopy combined with 3D image analysis techniques |
| Axial muscle fibre identification | Genetically modified line of zebrafish that expresses green fluorescent protein (GFP) solely in their white axial muscle fibres |
| Axial muscle development | Initiates within the paraxial mesoderm, which segments along the anteroposterior axis to form blocks of cells called somites |
| Axial muscle function | Generates undulatory locomotion through wave-like contractions along the length of the body that propel the fish forward |
| Axial muscle regeneration | Skeletal muscles can regenerate after minor injuries, but severe structural damage can lead to fibrosis |
| Axial muscle innervation | Spinal motor neurons and peripheral motor nerves form discrete motor units that execute movements of varying force and speed |
| Axial muscle composition | Comprised of fast-twitch ('white') fibres and slow-twitch ('red') fibres |
| Axial muscle location | Under the skin, covered by a thin layer of red muscle fibres |
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What You'll Learn
Axial muscle fibres in larval zebrafish
The axial muscles in larval zebrafish grow quickly and increase in complexity. They are covered by a thin layer of red muscle fibres, under which lie the fast axial muscle fibres. During early development, the muscle fibres change orientation from approximately longitudinal at 1 dpf to a pseudo-helical arrangement at 3 dpf. This rearrangement is likely co-regulated by gene expression and muscle activity.
Previous research into the muscle architecture of larval fish primarily relied on histological sections, which can cause tissue distortion and typically only cover a specific area of the fish. More recently, researchers have utilized high-resolution confocal laser microscopy combined with 3D image analysis techniques to assess muscle-fibre orientations across the whole axial musculature. This has allowed for the creation of a comprehensive quantitative description of the muscle-fibre orientations in the entire axial musculature of a living teleost fish.
In addition, the use of genetically modified zebrafish that express green fluorescent protein (GFP) solely in their white axial muscle fibres has facilitated the segmentation and identification of individual fibres. This methodology offers a promising avenue for exploring muscle-fibre orientations across ontogenetic series and provides a foundation for in-depth functional studies on the role of muscle architecture in facilitating swimming performance.
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Axial muscle architecture in larval zebrafish
Zebrafish have been used as a model system for investigating muscle patterning and growth due to their simple axial musculature with spatially separated fibre types. The axial muscle is the most abundant tissue type in the fish body and functions to produce undulatory locomotion, or wave-like contractions, that propel the fish forward.
The axial muscle architecture in larval zebrafish has been the subject of several studies, with a focus on understanding the changing architecture during larval development. Histological studies have shown that in larval fish, muscle fibres in the anal region transition from an almost longitudinal orientation to a pseudo-helical pattern by 3 days post-fertilisation (dpf). However, these studies have been limited to specific sections of the body and have been prone to shrinkage and tissue damage.
To address these limitations, researchers have developed novel methodologies that utilise high-resolution three-dimensional scans of live, anaesthetised larval fish at 4 dpf. This technology allows for a comprehensive analysis of the entire axial musculature and enables the quantification of muscle-fibre orientations across the entire muscle. By using genetically modified zebrafish that express green fluorescent protein (GFP) solely in their white axial muscle fibres, researchers can easily identify and segment individual fibres for analysis.
These studies have revealed that in 4 dpf zebrafish larvae, the fast axial muscle fibres follow helical trajectories that taper towards the tail. The muscle-fibre architecture at this stage is believed to contribute to the swimming performance of the larvae, allowing them to overcome high viscous forces and achieve higher tail-beat amplitudes and frequencies compared to adult fish.
Overall, the axial muscle architecture in larval zebrafish is a dynamic and complex system that undergoes significant changes during early development. The utilisation of novel methodologies and genetic techniques provides valuable insights into the structure and function of axial muscles in larval zebrafish.
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Axial muscle regeneration in adult zebrafish
Zebrafish are an important and accessible laboratory model organism, sharing similarities with mammalian embryonic musculoskeletal development. They are particularly useful for studying axial muscle regeneration due to their simple axial musculature with spatially separated fibre types.
In zebrafish, axial muscle is the most abundant tissue type in the body, functioning to produce undulatory locomotion. Axial musculature development, or primary myogenesis, initiates within the paraxial mesoderm, which segments along the anteroposterior axis to form blocks of cells called somites. The paraxial mesoderm also undergoes morphogenetic changes to form distinct cell populations, including adaxial cells, the primary myotome, and the dermomyotome-like external cell layer.
During early development, muscle fibres change orientation from approximately longitudinal at 1 day post-fertilisation (dpf) to a pseudo-helical arrangement at 3 dpf. This rearrangement is likely co-regulated by gene expression and muscle activity. New muscle fibres are generated laterally and migrate inwards, growing in length and width.
In terms of regeneration, zebrafish axial muscles can regenerate after minor injuries. However, it is unknown whether adult zebrafish can regenerate severely destroyed musculature. A cryoinjury model revealed that several myomeres efficiently regenerated within one month after wounding the caudal peduncle. This regeneration involved the accumulation of the selective autophagy receptor p62, an immune response, and Collagen XII deposition. New muscle formation was associated with the proliferation of Pax7-expressing muscle stem cells, which gave rise to MyoD1-positive myogenic precursors, followed by myofiber differentiation.
In summary, zebrafish provide an attractive model for studying axial muscle regeneration due to their simple axial musculature and ability to regenerate muscle after minor injuries. Further research is needed to understand their capacity for regeneration after severe muscle damage.
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Axial muscle development in zebrafish larvae
The zebrafish has been an attractive model system for investigating muscle patterning and growth due to its simple axial musculature with spatially separated fibre types. Zebrafish larvae muscles can be examined in vitro using mechanical and x-ray methods. The muscles and myofilaments are mainly oriented in parallel with the larvae's long axis and exhibit a significant fast contractile component. Sustained contractions can also involve a small contribution from slower muscle types.
During early development, the muscle fibres change orientation from approximately longitudinal at 1 dpf to a pseudo-helical arrangement at 3 dpf. This rearrangement is presumably co-regulated by gene expression and muscle activity, but is still insufficiently understood. In the anal region of larval zebrafish, the pseudo-helical pattern is less pronounced than in juvenile zebrafish. Other sections of the body were not investigated, although adult fish show a morphological difference over the longitudinal axis, and the curvature amplitude during swimming varies along the fish, which affects the strain amplitude.
To understand the functioning of the axial muscles during swimming in larval fish and how this changes during development, it is essential to analyse the orientation of muscle fibres across the entire muscle volume. Previous research into the muscle architecture of larval fish primarily relied on histological sections, which can cause tissue distortion and typically only cover a specific area of the fish. A novel method for accurately mapping the complete three-dimensional structure of axial muscle fibres throughout the entire body of a larval fish has been introduced. This method utilizes high-resolution confocal laser microscopy combined with 3D image analysis techniques to assess muscle-fibre orientations across the whole axial musculature.
For the identification of individual fibres, a genetically modified line of zebrafish that expresses green fluorescent protein (GFP) solely in their white axial muscle fibres has been employed. This allows for the segmentation of these fibres, with random variations in expression levels facilitating the segmentation of these fibres.
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Axial muscle fibre orientation in larval zebrafish
Zebrafish have provided an attractive model system for investigating muscle patterning and growth due to their simple axial musculature with spatially separated fibre types. In fishes, axial muscle is the most abundant tissue type in the body and functions to produce undulatory locomotion: wave-like contractions along the length of the body that propel the fish forward.
During early development, muscle fibres change orientation from approximately longitudinal at 1 dpf to a pseudo-helical arrangement at 3 dpf. This rearrangement is presumably co-regulated by gene expression and muscle activity, but is still not fully understood. In 4 days post-fertilization zebrafish larvae, the fast axial muscle fibres follow helical trajectories that taper towards the tail.
In addition, the axial muscles in larval fish grow quickly and increase in morphological and physiological complexity. They also swim at high tail-beat frequencies, which are achieved through very fast embryonic or larval muscle-fibre types that differ from the equivalent juvenile and adult fibre types.
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Frequently asked questions
Axial muscle is the most abundant tissue type in the body of fishes and functions to produce undulatory locomotion.
Axial muscle zebrafish is a type of zebrafish that expresses green fluorescent protein (GFP) solely in their white axial muscle fibres. This allows for the segmentation and identification of individual fibres.
The structure of axial muscle zebrafish is described as a closely packed array of nested pseudo-helical muscle-fibre trajectories. The muscle fibres are arranged in complex, three-dimensional patterns rather than being oriented parallel to the longitudinal axis of the body.
Larval zebrafish swim primarily using their axial musculature, which can generate tetanic forces. They use fast-twitch, 'white' fibres that make up the bulk of the muscle mass and a superficial layer of slow, 'red' fibres.
The zebrafish has been used as a model system for investigating muscle patterning and growth due to its simple axial musculature with spatially separated fibre types. Zebrafish embryos and larvae are also transparent and develop rapidly, making them useful for genetic and functional studies.
