Question

Why does meroblastic cleavage occur? Identify the different kinds of gastrulation: invagination, involution, ingression, delamination, epiboly, and which animals and tissues gastrulated by which processes? Which tissues were formed? How are both mesenchyme cells and epithelial cells important in neurulation? How are cadherin molecules important? Compare and contrast secondary and primary neurulation. What is the Epithelial mesenchymal transition? Understand the signaling of Shh and TGF-beta and BMP in the specification of the neural tube

Answer 1

1.     Differentiation of cells through cell division in early embryo development stage referred as cleavage. In the case of zygote the original size of zygote will not change but produces the cluster of cells through rapid cell division produces the compact mass called morula.

This cleavage depends upon the amount of yolk in egg, which can leads to partial or complete cleavage. In presence of large amount of yolk the egg cell will undergo partial cleavage is known as meroblastic. This meroblastic is further subdivided in two types i.e. discoidal and superficial.      

2.     Gastrulation divided into basic five types which cover the complete animal kingdom. These types are given below:-

1)    Invagination: - It is a morphogenetic process which involves the reorganization of embryo which converted into multilayered organism from simple spherical blastula.

2)    Involution: - Involution refers as the size modification due to proteolysis of basal lamina which leads to decrease in cell number and decrease in size of an organ.

3)    Ingression: - Ingression is the change which will occur because of the change in location and position of cells. This happens during the process of gastrulation in animal development to produce mesenchyme cells. .   

4)    Delamination: - It represents the separation of layers or cells at early stage of development where blastoderm of embryo splits into two layers.

5)    Epiboly. It defines the cell movement in early embryo development stage at the time gastrulation which brings the changes in physical structure.

3.     During the process of neurulation the neural tube synthesis occur at the dorsal midline. At same time the neural crest cells forms the roof plate through transition from epithelial to mesenchymal of neural tube.   

4.     Cadherins are the molecules which help in cell adhesion through synthesis of adherens junctions with help of calcium ions and bind with cells. These are the part of trans-membrane protein categorized in class-1. They helps in proper separation and cellular migration.