Flashcards in Lect. 14 - Establishment Of Body Plan I Deck (14):
What is the process of convergent extension?
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.
What role does planar polarity play in the formation of the neural plate?
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
What is the significance of the median hinge point in neural tube formation?
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
What is the significance of the lateral hinge point in neural tube folding?
Involves apical constriction by actin filaments so cells become pyramidal
What role does RA play in the segmentation of the spinal cord?
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
What role does Otx-2 play in the segmentation of the spinal cord?
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
What role does Gbx-2 play in the segmentation of the spinal cord?
Expressed in the hindbrain region resulting from the anterior notochord; works w/ Otx-2 to establish a signaling center in isthmic organizer
What role does Wnt-8 play in the segmentation of the spinal cord?
Establishes the anterior-posterior gradient
What role does Shh play in the segmentation of the spinal cord?
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
What role does FGF-8 play in the segmentation of the spinal cord?
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
What are the stages in neural tube development?
1. Formation of thickened neural plate; 2. Shaping of neural plate; 3. Folding of neural plate; 4. Formation of neural tube.
What role does Krox 20 play in the segmentation of the hindbrain?
Helps set up basic pattern of segmentation in hindbrain: Krox 20 --> r3 and r5
What role do Kreisler and Hoxa-1 play in segmentation of the hind brain?
Help set up basic pattern of segmentation; Kreisler and Hoxa-1 --> r5