What is Gastrulation?
We all know that giving birth to the organisms including mammals is considered as one of the vital process in every class of animals as it gives rise to next generation. Formation of the embryo, is a very complex process and it involves various process of developmental stages.
Embryogenesis is one of important field in the biology, it is the first eight-week process of development after fertilization. It is one of the amazing and the complicated process where a single cell is transferred into the multi-level body. During this stage, circulatory, excretory and the neurologic systems which all being to develop at this stage.
The terms Gastrula and the Gastrulation was first coined by the scientist named Ernst Haeckel in the year 1872 during his work on Sponges. Each species has its own gestation period. Human embryogenesis is one of the complex process which occurs during the first wight weeks of the gestation period after the process of fertilization.
This process begins by fertilization of an egg or ovum by the sperm and results in formation of a zygote. The zygote is a cell which is surrounded by a strong membrane and is made up of glycoproteins, where the fertilization occurs after penetration of the sperm.
After this process, the zygote undergoes various cell divisions by the process of cleavage, Gastrulation is one among them and it is discussed as follows.
Gastrulation plays an important role in developmental biology during the embryonic development of most of the animals. In gastrulation blastula changes from its single layered hollow sphere of cells into a multilayered structure.
Before the process of gastrulation, the embryo continuous to form an epithelial sheet of cells by end of the gastrulation process and the embryo begins to differentiate and establish the distinct cell lineages, by setting up the basic axed needed for the body such as dorsal-ventral anterior position and the prospective gut formation.
In the triploblastic organisms, the gastrula is a three layered, which is known as trilaminar. The three germ layers are differentiated as ectoderm, mesoderm and the endoderm. Ectoderm forms an outer layer; mesoderm forms a middle layer and the endoderm forms an inner layer.
In diploblastic organisms, the gastrula is formed with two distinct germ layers namely ectoderm and the endoderm. Examples of diploblastic organisms include Cnidaria and the Ctenophora.
Gastrula containing only two layers are sometimes referred to as hypoblast and the epiblast.
Generally, the process of gastrulation occurs after the cleavage process which occurs after the stage of blastula. Further the process of organogenesis, where the individual organs start arising and give rise to newly formed germ layers.
Further these layers give rise to specific tissues and the organs in the developing embryo. As mentioned above, the gastrula is formed of three germ layers namely ectoderm, endoderm and the mesoderm. In which ectoderm gives rise to epidermis, the nervous system and in forming the neural crest in the vertebrates.
The endoderm results in the formation of the epithelium of the digestive system and in forming the respiratory system and the other organs which are all associated with the digestive system including those of pancreas and the liver.
From mesoderm arises many types of cells such as bone, muscle and other connective tissues of the body, especially in vertebrates, the mesoderm gives rise to notochord, the near and the blood vessels, blood, cartilages, ribs and it is also associated with formation of the dermis.
After completing the process of gastrulation, our body is organized into the either the sheets od the connected cells as of epithelia or into a mesh of the isolated cells, as of mesenchyme.
Though the process of gastrulation exhibits various patterns of changes and classification in the animal kingdom there are very important and they are unified by the presence of five basic types of cellular movements which involves during the process of gastrulation. They are invagination, involution, ingression, delamination and Epiboly.
Gastrulation and Cellular Signalling
During the process of gastrulation, the cells are differentiated usually into two layers as ectoderm or me endoderm, when then the mesendoderm is further divided into mesoderm and endoderm, this differentiation occurs due to the nodal signaling.
Nodal signaling uses ligands which belongs to the family of TGFβ. These ligands play a role in signaling to the transmembrane serine or threonine kinase receptors and this will then it attaches itself against the Smad2 and Smad3. This protein then attaches itself against the Smad4 and it relocates it to the nucleus where the mesendoderm genes are transcribed.
The Wnt pathway along with the Beta-catenin plays an important role in performing the nodal signaling and in the formation of the endoderm. Then the other factors like Fibroblast growth factors, canonical Wnt pathway, bone morphogenetic protein and retinoic acid is important for the development of the endoderm.
These are considered as very much significant in forming the gene known as homeobox, which is helpful in regulating the early development of the anatomical features. Bone Morphogenetic Protein plays a vital role in detecting the fate of the liver and the hepatic cells. Retinoic acid signaling also results in initiating the induction of the homeobox genes.