“It is not birth, marriage or death, but gastrulation which is truly the most important time in your life.”
— Lewis Wolpert
Overview of pre-gastrulation embryos
Overview of pre-gastrulation embryos
The fertilization of an egg cell, resulting in the formation of a zygote, marks the beginning of embryonic development.
Through a series of cleavages, the zygote transforms into a cluster of cells known as a morula (16-32 cells).
After that, The transition to a blastula occurs when the blastocoel (a fluid-filled cavity) is established.
The blastula precedes the development of a gastrula (gastrulation), wherein which the germ layers of the embryo take shape.
Key Cellular Movements during Gastrulation
Key Cellular Movements during Gastrulation
Gastrulation is a crucial phase in embryonic development during which a blastula undergoes significant cellular movements and rearrangements to establish the three primary germ layers: ectoderm, mesoderm, and endoderm. These movements are essential for the formation the subsequent development of various tissues and organs.
Here are some key cellular movements during gastrulation:
Involution
It involves the inward movement or rolling of a sheet of cells into the embryo. The cell sheet spreads over the internal surface of the original outer cell layer.
Example: the formation of the mesoderm germ layer in amphibian.
Delamination
Splitting of one sheet of cells into parallel sheets. On a cellular level, it resembles ingression, but the result is the formation of new epithelial cell layer(s).
Example: the formation of the hypoblast in birds and mammals.
Invagination
Cells at the surface of the blastula fold inward, creating a depression or invagination.
Example: the formation of the endoderm germ layer in sea urchin.
Ingression
Individual cells detach from the epithelial cell layer and migrate into the embryo's interior. The cells become mensechymal (i.e., separate from one another) and migrate independently.
Example: the formation of the mesoderm germ layer in sea urchin.
Epiboly
Movement of outer epithelial sheets (typically the ectoderm), spreading out as a unit over the inner layer of the embryo. This movement can occur by cells dividing, by cells changing their shape, or by several layers of cells radially intercalating into fewer layers; often, all three mechanisms are used.
Example: the formation of the ectoderm in sea urchins, tunicates, amphibians, and zebrafish.
