Somitogenesis Flashcards
what is somitogenesis?
- Process of somite formation from the paraxial mesoderm.
- Sequential budding off of somites from the anterior part of the presomitic mesoderm.
what is paraxial mesoderm?
- One of the three primary germ layers in vertebrate embryos.
- Lies on either side of the midline, adjacent to the notochord and neural tube.
- Gives rise to somites during somitogenesis.
what is axial mesoderm?
- Also known as the notochordal mesoderm or notochord.
- Specialized rod-like structure along the midline, underneath the neural tube.
what is the role of the Notochord?
- provides signals and organizes the axial pattern of the developing embryo.
- imparts axial identity to the somites before they form.
Axial Identity of Somites
- determined by signals from notochord during somite formation.
- Noggin, secreted by the notochord, antagonizes BMP signaling to allow somitogenesis and form segmented somites with distinct axial identities
what are somites?
- bilateral pairs of mesoderm that form on either side of the neural tube along the anterior-posterior (AP) axis (of the developing embryo)
- play crucial role in forming vertebral column, associated musculature & organizing peripheral nerves.
How are somites derived?
- somites bud off from the anterior part of the presomitic mesoderm as it extends posteriorly during gastrulation
- identity of somites is imparted in the presomitic mesoderm before somite formation occurs.
what are the derivatives of somites?
Somites become regionalized into three compartments: sclerotome (forms vertebral column), myotome (forms muscles), and dermatome (forms dermis)
What are the derivatives of the sclerotome, myotome, and dermatome?
- Sclerotome gives rise to the vertebral column and rib cartilage.
- Myotome forms the muscles of the body.
- Dermatome forms the dermis of the skin.
How is the regionalization of somites influenced?
regionalization of somites is dependent upon signals from surrounding tissues, including the neural tube and surface ectoderm
How are somites divided?
Somites are divided into anterior and posterior halves
How do somites impact the development of the peripheral nervous system?
posterior halves of somites repulse axons and neural crest cells, organizing the formation of spinal nerves.
What is scoliosis?
a defect of the somites that results in abnormal curvature of the spine
What is the axial identity of somites, and how is it established?
- Somites have axial identity, which is determined and remembered in the presomitic mesoderm before somite formation.
- Experiments, including somite transplantation and rotation of presomitic mesoderm, have demonstrated the role of Hox genes in axial identity.
How do signaling molecules regulate somitogenesis?
- Notch-Delta (DII1 in mice) signaling in the presomitic mesoderm is required for somitic segmentation.
- BMP signaling from the lateral plate mesoderm can be antagonized by Noggin from the notochord, allowing somite formation in the paraxial mesoderm.
What is the clock and wavefront mechanism in somitogenesis?
- During chick somitogenesis, pre-segmental mesoderm cells switch between states in waves
- with cHairy1 being an example of a transcription factor showing a wave of expression.
How are somites compartmentalized and differentiated?
- Somite epithelialization depends on signals from the neural tube and surface ectoderm.
- The somites are further divided into sclerotome, myotome, and dermatome compartments with specific transcription factors and signaling molecules controlling their development.
What are the stages of somitogenesis?
- Paraxial mesoderm segmentation
- Somite epithelialization
- Anteroposterior subdivision
- Regionalization of somites
What is the first stage of somitogenesis?
Paraxial Mesoderm Segmentation
Involves the sequential budding off of somites from the anterior part of the presomitic mesoderm.
What process follows somite segmentation?
- Somite Epithelialization
- Involves the transformation of somite cells from a mesenchymal to an organized epithelial structure.
What happens during the third stage of somitogenesis?
- Anteroposterior Subdivision
- Somites become subdivided into compartments, such as sclerotome, myotome, and dermatome.
What is the final stage of somitogenesis?
- Regionalization of Somites
- Somites further differentiate into specific tissues like vertebral column, muscles, and dermis.
What is the final stage of somitogenesis?
- Regionalization of Somites
- Somites further differentiate into specific tissues like vertebral column, muscles, and dermis.
What is the clock and wavefront mechanism?
A fundamental process in somitogenesis, the formation of somites during embryo development
What does the “clock” represent in somitogenesis?
A molecular oscillation in the presomitic mesoderm that creates periodic gene expression
What is the “wavefront” in somitogenesis?
A moving boundary that determines where somites will form along the embryo’s axis
How do the “clock” and “wavefront” interact?
The “wavefront” synchronizes with the “clock” at specific sites, leading to the formation of somites
Why is the clock and wavefront mechanism important?
ensures the precise and sequential development of somites in the embryo.
What is the relevance of this mechanism to neuroscience studies?
- Proper somite formation is crucial for organizing neural structures along the body axis
somites are key features of what?
- Key features of vertebrate embryos.
- Blocks of tissue that form in pairs on both sides of the neural tube.
At each axial level, each somite will generate what?
- Sclerotome – forms cartilage of the vertebrae
- Myotome – forms muscle
- Dermatome – forms dermis
- Syndetome - forms tendon
What is the role of Wnt6 in somitogenesis?
- Wnt6 promotes the epithelialization of the somite dermamyotome
- gives rise to both the dermis (connective tissue of the skin) and the myotome (muscle-forming region)
- Wnt6 expression in the somite facilitates the transition of mesenchymal cells into epithelial cells, contributing to the proper differentiation and development of dermal and muscular components
