Axial Skeleton Development

Question 1

What is the axial musculoskeletal system?

Answer 1

It is one of the more complex and fascinating aspects of developmental biology with important clinical implications.

Question 2

What are somites?

Answer 2

Somites are repeating blocks of mesoderm along the axial midline.

Question 3

What is somatogenesis?

Answer 3

Somatogenesis is the development of somites, an evolutionarily conserved process that occurs in all vertebrates.

Question 4

What structures are derived from somites?

Answer 4

Somites give rise to the dermis of the skin, all skeletal muscle, and the axial skeleton, including bone and cartilage.

Question 5

What is the focus of today’s discussion?

Answer 5

Today’s discussion focuses on the development of part of the axial skeleton, specifically the neck and trunk.

Question 6

What is the mesoderm?

Answer 6

The mesoderm is the middle of the three germ layers established from gastrulation.

Question 7

What is paraxial mesoderm?

Answer 7

Paraxial mesoderm is the mesoderm closest to the midline axis and the notochord, from which somites develop.

Question 8

What are somitomeres?

Answer 8

Somitomeres are thickened paraxial mesoderm at the cranial end of the embryo that do not divide into clear somites.

Question 9

How are somites formed?

Answer 9

Somites are formed in a cranial to caudal fashion from the presomitic mesoderm.

Question 10

What are the gradients involved in somite formation?

Answer 10

There are opposing gradients of WNT signaling molecules and retinoic acid at the level of somite formation.

Question 11

What is the segmentation clock?

Answer 11

The segmentation clock refers to the oscillatory expression of genes involved in somite formation.

Question 12

How often are new somites formed in the mouse?

Answer 12

New somite pairs are formed in the mouse at regular two-hour intervals.

Question 13

How can somites be used in research?

Answer 13

Somites can be counted to determine the precise biological age of embryos due to their regular periodicity of formation.

Question 14

Do somites look uniform?

Answer 14

Initially, each of the somites looks relatively uniform along the cranial to caudal axis.

Question 15

What is the significance of somite formation in embryonic development?

Answer 15

Somite formation allows researchers to determine the precise biological age of an embryo due to the regular periodicity of new somite formation.

Question 16

What do somites differentiate into?

Answer 16

Somites differentiate into three distinct regions: sclerotome, dermatome, and myotome.

Question 17

What does the sclerotome give rise to?

Answer 17

The sclerotome gives rise to cartilage and bone.

Question 18

What does the dermatome form?

Answer 18

The dermatome forms the dermis of the skin.

Question 19

What is the role of the myotome?

Answer 19

The myotome forms all of the skeletal muscle in the body.

Question 20

What is sonic hedgehog’s role in somite differentiation?

Answer 20

Sonic hedgehog signaling molecules induce differentiation of the closest regions of the somites into sclerotome.

Question 21

What happens during sclerotome resegmentation?

Answer 21

The loosely packed cranial portion of sclerotome from one somite resegments with the densely packed caudal part of its neighbor.

Question 22

What is the function of the myotome in relation to vertebrae?

Answer 22

The myotome spans across vertebrae, serving as a muscular bridge.

Question 23

What are the two components of intervertebral discs?

Answer 23

The two components are the annulus fibrosis, formed from sclerotome, and the nucleus pulposus, thought to be remnants of the notochord.

Question 24

What are the two basic mechanisms of vertebral ossification?

Answer 24

The two mechanisms are intramembranous ossification and endochondral ossification.

Question 25

What is the epimere and hypomere in myotome development?

Answer 25

The epimere gives rise to extensor muscles, while the hypomere gives rise to flexor muscles of the vertebral column.

Question 26

What can disrupt somatogenesis and sclerotome resegmentation?

Answer 26

Disruptions can result in vertebral defects or malformations, such as hemivertebrae and block vertebrae.

Question 27

What is a hemivertebral abnormality?

Answer 27

A hemivertebral abnormality consists of wedge-shaped pieces of abnormal vertebrae between neighboring vertebrae.

Question 28

What are block vertebrae?

Answer 28

Block vertebrae occur when two or more vertebrae are fused.

Question 29

What is the relationship between corkscrew tails and vertebral malformations?

Answer 29

Corkscrew tails in some breeds are often the result of vertebral malformations that can affect somite development.

Question 30

What are corkscrew tails in animals?

Answer 30

Corkscrew tails are considered a desired trait for some breeds, but they are often the product of vertebral malformations.

Question 31

How do genetic variants affect corkscrew tails?

Answer 31

Genetic variants selected for corkscrew tails can impact somite development in both the tail region and the cranial aspect of the spinal column.

Question 32

What should be done for animals with corkscrew tails experiencing neurological symptoms?

Answer 32

Radiographs should be performed to assess the development of the vertebrae.

Question 33

What can be observed on radiographs of animals with corkscrew tails?

Answer 33

Radiographs may show vertebral malformations that form the corkscrew tail.