Lect. 14 - Establishment Of Body Plan I

Question 1

What is the process of convergent extension?

Answer 1

Occurs during the shaping of neural plate; involves migration of ectodermal cells toward midline; ectodermal cells elongate along the ant-post axis and become thinner, forming an elongated, narrow plate.

Question 2

What role does planar polarity play in the formation of the neural plate?

Answer 2

PCP (planar cell polarity) convert elliptical gastrula into keyhole-shaped neurula and are important in the folding of the neural plate into neural tube; PCP pathway is highly conserved involving canonical Wnt/frizzled/disheveled signaling cascade; in its absence, neural folds remain far apart and neural tube closure is absent

Question 3

What is the significance of the median hinge point in neural tube formation?

Answer 3

Median hinge point is induced by the notochord; involves changes in shape of columnar cells to pyramidal-shaped cells via apical constriction; require synthesis of actin filaments at apical ends of cells

Question 4

What is the significance of the lateral hinge point in neural tube folding?

Answer 4

Involves apical constriction by actin filaments so cells become pyramidal

Question 5

What role does RA play in the segmentation of the spinal cord?

Answer 5

Differentiation of the cells that fall out of the stem cells zone are under the influence of RA produced by flanking somites; RA blocks FF-8 and Wnt-3a

Question 6

What role does Otx-2 play in the segmentation of the spinal cord?

Answer 6

Expressed in the forebrain/midbrain region resulting from the head organizing region; also works w/ Gbx-2 to establish a signaling center in the isthmus organizer

Question 7

What role does Gbx-2 play in the segmentation of the spinal cord?

Answer 7

Expressed in the hindbrain region resulting from the anterior notochord; works w/ Otx-2 to establish a signaling center in isthmic organizer

Question 8

What role does Wnt-8 play in the segmentation of the spinal cord?

Answer 8

Establishes the anterior-posterior gradient

Question 9

What role does Shh play in the segmentation of the spinal cord?

Answer 9

Secreted by anterior neural ridge signaling center (organizes telencephalon, die cephalon, olfactory area and pit. Gland) and also the zona limitans (organizes border b/w dorsal and ventral thalamus) signaling center

Question 10

What role does FGF-8 play in the segmentation of the spinal cord?

Answer 10

Released posteriorly by the isthmic organizer and along w/ Wnt-1 it induces gradients of En-1 and En-2; also secreted by presomitic mesoderm flanking post. Regions of neural tube and it maintains cells in proliferative state; blocked by RA

Question 11

What are the stages in neural tube development?

Answer 11

1. Formation of thickened neural plate; 2. Shaping of neural plate; 3. Folding of neural plate; 4. Formation of neural tube.

Question 12

What role does Krox 20 play in the segmentation of the hindbrain?

Answer 12

Helps set up basic pattern of segmentation in hindbrain: Krox 20 –> r3 and r5

Question 13

What role do Kreisler and Hoxa-1 play in segmentation of the hind brain?

Answer 13

Help set up basic pattern of segmentation; Kreisler and Hoxa-1 –> r5

Question 14

What role does RA play in the segmentation of the hind brain?

Answer 14

Helps set up basic pattern of segmentation; RA gradient –> r4-r7; RA gradient stimulates expression of Hoxa-1 and Hoxa-2 which determine cranial nerves and pharyngeal arch derivatives