Question

Question 4 Topic: Gastrulation in sea urchin (8 points) a) Choose one of the cell behaviors listed below and explain how it contributes to the process of gastrulation in sea urchins. In your answer be sure to describe how this cell behavior happens and the specific step in gastrulation where this cell behavior takes place. Some of these behaviors work in more than one step, you only need to explain its role in one. epithelial to mesenchymal transition apical constriction convergent extension (intercalation) filapodia

Answer 1

Role of APICAL CONSTRICTION in Gastrulation on sea urchins:

• Sea urchins are echinoderms and belong to the class of :Echinoidea

Gastrulation is the period during the early development of animals when major cell and tissue movements remodel an initially unstructured group of cells.

It requires coordinated control of different types of cellular activities in different cell population.

1. In amphibian embryos, apical constriction of bottle cells leads to the formation of the dorsal lip, which marks the initiation of gastrulation. The cells on the vegetal surface of the embryo become columnar, forming the vegetal plate.   

• In certain species of sea urchin, a ring of cells along the edges of the vegetal plate has been recognized to undergo more pronounced apical constriction.Cells in this ring have been referred to as bottle cells.

2.  The surface of this plate bends inward, a process termed apical constriction or primary invagination .RhoA is required for the initiation of primary invagination.Apical constriction is the active narrowing of cellular apices.

3. Contraction of an apical microfilament network is not the only way apical constriction can take place. A shrinking of the apical side of a cell may also be driven by basolateral lengthening or expansion, movement of apical surface to lateral domains, or by extracellular forces

Importance of Apical Constriction :

• Occurs at early stages of embryogenesis
• Helps to expose the links between early patterning processes, such as cell fate specification or apico-basal cell polarization.
• Helps to explore the mechanisms that produce force which aids in bending of the vegetal plate.