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Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body (e.g. dorsal–ventral, anterior–posterior), and internalized one or more cell types including the prospective gut.
Epiboly in zebrafish is the first coordinated cell movement, beginning at the dome stage late in the blastula period and continuing throughout gastrulation. [3] At this point the zebrafish embryo contains three portions: an epithelial monolayer known as the enveloping layer (EVL), a yolk syncytial layer (YSL) which is a membrane-enclosed group of nuclei that lie on top of the yolk cell, and ...
During gastrulation cells migrate to the interior of the blastula, subsequently forming two (in diploblastic animals) or three (triploblastic) germ layers. The embryo during this process is called a gastrula. The germ layers are referred to as the ectoderm, mesoderm and endoderm.
Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. [4] During this time three cell populations become distinguished. The first population is the yolk syncytial ...
The archenteron, also called the gastrocoel, the primitive digestive tube or the primitive gut, is the internal cavity of the primitive gastrointestinal tract that forms during gastrulation in a developing animal embryo. It develops into the endoderm and mesoderm of the animal.
An alternative way to develop two openings from the blastopore during gastrulation, called amphistomy, appears to exist in some animals, such as nematodes. [3] [4] In humans, the perforation of the mouth and anus happen at four weeks and eight weeks respectively. [5]
The chordamesoderm has two components: the head process and the notochord. The most anterior part, the head process, is formed by central mesoderm cells migrating anteriorly, behind the prechordal plate mesoderm and toward the rostral tip of the embryo. The head process will underlie those cells that will form the forebrain and midbrain.
Sea urchin gastrulation is another classic model for invagination in embryology. One of the early gastrulation movements in sea urchins is the invagination of a region of cells at the vegetal side of the embryo (vegetal plate) to become the archenteron, or future gut tube. There are multiple stages of archenteron invagination: a first stage ...