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 Interactive Fly, Drosophila Goosecoid: Biological Overview
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