Thus Gsc is expressed in the foregut of both flies and vertebrates. In vertebrates, Gsc is expressed in the dorsal lip of the blastopore, the region leading the invagination of the mesoderm during gastrulation that will give rise to the head process and the anterior-most tissues of the vertebrate embryo (prechordal plate mesoderm). The stomatogastric nervous system is believed to arise from the labrum, the most anterior embryonic segment (Schmidt-Ott, 1994). In Drosophila the cells invaginating in the stomodeum (those that express Gsc) constitute the anterior-most structure of the embryo. In all Protostomes, the stomodeum is the anterior end of the blastopore. What is evolutionarily conserved with respect to GSC function when comparing between vertebrates and invertebrates? Any comparison is complicated by the fact that vertebrates are Deuterostomes (the mouth forms as a secondary consequence far away from the blastopore, which gives rise to the anus), while insects are Protostomes (the mouth forms at or near the blastopore). Thus Goosecoid appears to mimic properties of the "organizer" (Niehrs, 1993). The migrating cells contribute mainly to the most anterior involuting tissues, namely anterior endoderm and head mesoderm. Goosecoid expressing cells induce neighboring cells to migrate toward the anterior of the embryo and enhance involution. Goosecoid expression in vertebrates takes place in the organizer, the compartment associated with the dorsal lip of the blastopore which functions in the recruitment of cells for involution through the blastopore and is responsible for self-determination of cells into dorsal mesoderm. During early cellularization an expression domain anterior to the cephalic furrow gives rise to cells that ultimately will be located in the brain hemispheres, while a second domain invaginates inside the stomodeum along with ectodermal cells to give rise to the stomatogastric nervous system, ring gland and foregut. The Drosophila Goosecoid homolog is expressed in two domains during embryogenesis. Keywords - Brain, stromatogastric nervous system, foregutĬlassification - Homeodomain - paired-type This area of cells opposite the point of sperm entry will form the blastopore and become the dorsal portion of the body.Interactive Fly, Drosophila Goosecoid: Biological Overview The microtubules of the sperm direct cytoplasmic movements that empower the vegetal cells opposite the point of sperm entry to cause the blastopore in the mesoderm above them. The vegetal cells are crucial in identifying the place of the blastopore, as is the point of sperm entry. The remaining patch of the endoderm cells is called the yolk plug, and it also ultimately internalized.Īt this point, all the endodermal precursors have been brought into the interior of the embryo, the ectoderm has actually surrounded the surface and the mesoderm has been brought between them. The closing cells of the blastopore constitute the yolk plug. The blastopore is gradually covered by specific endoderm cells. Due to the formation of the ventral lip, there is a ring formed around endodermal cells. The widening blastopore finally develops the ventral lip over which mesodermal and ectodermal precursors cells pass. Blastocoel is displaced to the opposite side of the dorsal blastopore lip by new cells entering the embryo. These cells will form the notochord, a transient mesodermal “backbone” that plays an important role in differentiating and pattern the nervous system.Įxpansion of ectoderm is by epiboly. The next cells involuting into the embryo through the dorsal blastopore lip are called the chordamesoderm cells. As these very first cells enter the interior of the embryo, the dorsal blastopore lip ends up being made up of cells that involute into the embryo to become the prechordal plate (the precursor of the head mesoderm). These cells, later on, end up being the pharyngeal cells of the foregut. It is in a cylindrical form which is much longer on the dorsal than the ventral side. Blastocoel is reduced and the new cavity is formed by involuting cells, this is called Archenteron. The involuting cells gradually cover blastocoel. The invaginating endodermal cells move to the interior. The endodermal cells are first to invaginate and form archenteron. The cells at the animal pole undergo epiboly and converge blastopore. As invagination proceeds, there is the involution of marginal zone cells.
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