neural crest cells

Question 1

premigratory neural crest cells

Answer 1

cells at the regional interface are the neural plate border and have different specification
- as neural folds comes together, pre-migratory neural crest cells undergo EMT while neural tube and epidermal epithelia unite
- post EMT, migratory neural crest cells move throughout the developing embryo

Question 2

the Wnt/BMP code sets up expression of EMT regulatory factors that drive delamination of neural crest

Answer 2

-premigratory neural crest cells differentially express Cadherin-6B
-Wnt/BMP signaling promotes delamination (material fractures into layers) by upregulating EMT factors like Snail-2
- Snail 2 transcription factor downregulates Cadherin-6B and tight junction proteins, promoting de adhesion
-delaminating neural crest cells exhibit contact inhibition (change their direction of migration upon contact with another cell) of migration, helping cells to spread out during EMT

Question 3

How are neural crest cells specified?

Answer 3

• neural crest cells are specified at the neural plate boundary, suggesting that intermediate BMP signals may be important in this specification
  -intermediate levels of BMP signaling in the context of continuous Wnt signaling produces neural crest
  -this combinatorial signaling activates transcription factors that first specify the neural plate border, which in turn activate neural crest specifiers

Question 4

neural crest cells are multipotent progenitors

Answer 4

neural crest cells migrate throughout the embryo and develop into a variety of cell types and structures
-however, neural crest cells have different properties/potentials that depend upon their origin

Question 5

four major subdivisions of neural crest

Answer 5

(1) cranial
(2) cardiac
(3) trunk
(4) vagal and sacral

Question 6

neural crest is derived all along the A/P axis

Answer 6

the differential potentials of different types of neural crest seem to be due to differential Hox gene expression along the A/P axis

Question 7

cranial neural crest

Answer 7

these cells can become the same types of cells as trunk neural crest, but cranial can also form bone, cartilage, and connective tissue (mesoderm like)
-vertebrate head is largely comprised of neural crest derivatives
- midbrain, rhombomeres, jaw, middle ear bones, neurons of the teeth and eye, neck cartilage, facial nerves, etc

Question 8

cardiac neural crest

Answer 8

forms part of the heart and arteries
-contribute to arteries of the aortic arch and the septum between the aorta and pulmonary artery
- cardiac cells also contribute to the thyroid, thymus, and parathyroid glands

Question 9

trunk neural crest

Answer 9

migrate through either a dorsal or ventral pathway

dorsal; form pigment cells (melanocytes) and migrate between the dermis and epidermis, enter the ectoderm, and colonize the skin and hair follicles

ventral: becomes sensory and other neurons of the peripheral nervous system and glia; the cells move ventrally through the anterior sclerotome (somite mesoderm that forms spine cartilage)

Question 10

neural crest migration routes are directed by extracellular cues

Answer 10

• early migrating trunk neural crest is forced ventrally by several cues, such as Ephrins, becoming neurons
• ventral neural crest initially move between somites, but this is then blocked by Semaphorin-3F
• this forces neural crest to migrate through somites
• this migration is restricted to the anterior of the somite by anterior permissive signals;(fibronectin and laminin) and posterior blocking signals (Ephrins, Semaphorin 3F)
• later migrating cells switch to traveling dorsally and become pigment cells
• the switch is due to down regulation of transcription factor Foxd3, which allows expression of MITF, a transcription factor that specifies melanoblasts
• melanoblasts up regulate Ephrin receptor EphB2, which allows for migration along Ephrins