Somitogenesis

Question 1

what is somitogenesis?

Answer 1

• Process of somite formation from the paraxial mesoderm.
• Sequential budding off of somites from the anterior part of the presomitic mesoderm.

Question 2

what is paraxial mesoderm?

Answer 2

• 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.

Question 3

what is axial mesoderm?

Answer 3

• Also known as the notochordal mesoderm or notochord.
• Specialized rod-like structure along the midline, underneath the neural tube.

Question 4

what is the role of the Notochord?

Answer 4

• provides signals and organizes the axial pattern of the developing embryo.
• imparts axial identity to the somites before they form.

Question 5

Axial Identity of Somites

Answer 5

• 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

Question 6

what are somites?

Answer 6

• 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.

Question 7

How are somites derived?

Answer 7

• 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.

Question 8

what are the derivatives of somites?

Answer 8

Somites become regionalized into three compartments: sclerotome (forms vertebral column), myotome (forms muscles), and dermatome (forms dermis)

Question 9

What are the derivatives of the sclerotome, myotome, and dermatome?

Answer 9

• Sclerotome gives rise to the vertebral column and rib cartilage.
• Myotome forms the muscles of the body.
• Dermatome forms the dermis of the skin.

Question 10

How is the regionalization of somites influenced?

Answer 10

regionalization of somites is dependent upon signals from surrounding tissues, including the neural tube and surface ectoderm

Question 11

How are somites divided?

Answer 11

Somites are divided into anterior and posterior halves

Question 12

How do somites impact the development of the peripheral nervous system?

Answer 12

posterior halves of somites repulse axons and neural crest cells, organizing the formation of spinal nerves.

Question 13

What is scoliosis?

Answer 13

a defect of the somites that results in abnormal curvature of the spine

Question 14

What is the axial identity of somites, and how is it established?

Answer 14

• 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.

Question 15

How do signaling molecules regulate somitogenesis?

Answer 15

• 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.

Question 16

What is the clock and wavefront mechanism in somitogenesis?

Answer 16

• 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.

Question 17

How are somites compartmentalized and differentiated?

Answer 17

• 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.

Question 18

What are the stages of somitogenesis?

Answer 18

1. Paraxial mesoderm segmentation
2. Somite epithelialization
3. Anteroposterior subdivision
4. Regionalization of somites

Question 19

What is the first stage of somitogenesis?

Answer 19

Paraxial Mesoderm Segmentation
Involves the sequential budding off of somites from the anterior part of the presomitic mesoderm.

Question 20

What process follows somite segmentation?

Answer 20

• Somite Epithelialization
• Involves the transformation of somite cells from a mesenchymal to an organized epithelial structure.

Question 21

What happens during the third stage of somitogenesis?

Answer 21

• Anteroposterior Subdivision
• Somites become subdivided into compartments, such as sclerotome, myotome, and dermatome.

Question 22

What is the final stage of somitogenesis?

Answer 22

• Regionalization of Somites
• Somites further differentiate into specific tissues like vertebral column, muscles, and dermis.

Question 23

What is the final stage of somitogenesis?

Answer 23

• Regionalization of Somites
• Somites further differentiate into specific tissues like vertebral column, muscles, and dermis.

Question 24

What is the clock and wavefront mechanism?

Answer 24

A fundamental process in somitogenesis, the formation of somites during embryo development

Question 25

What does the “clock” represent in somitogenesis?

Answer 25

A molecular oscillation in the presomitic mesoderm that creates periodic gene expression

Question 26

What is the “wavefront” in somitogenesis?

Answer 26

A moving boundary that determines where somites will form along the embryo’s axis

Question 27

How do the “clock” and “wavefront” interact?

Answer 27

The “wavefront” synchronizes with the “clock” at specific sites, leading to the formation of somites

Question 28

Why is the clock and wavefront mechanism important?

Answer 28

ensures the precise and sequential development of somites in the embryo.

Question 29

What is the relevance of this mechanism to neuroscience studies?

Answer 29

• Proper somite formation is crucial for organizing neural structures along the body axis

Question 30

somites are key features of what?

Answer 30

• Key features of vertebrate embryos.
• Blocks of tissue that form in pairs on both sides of the neural tube.

Question 31

At each axial level, each somite will generate what?

Answer 31

• Sclerotome – forms cartilage of the vertebrae
• Myotome – forms muscle
• Dermatome – forms dermis
• Syndetome - forms tendon

Question 32

What is the role of Wnt6 in somitogenesis?

Answer 32

• 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