Gut Development

The ectodermal derivatives of the gut are the stomodeum and the proctodeum. The proctodeum is formed concurrently with germ-band elongation [Images] while formation of the foregut continues later and is associated with head involution. Adult foregut consists of the esophagus, pharynx, crop and the sucking pump or cibarium found at the base of the proboscis. Salivary gland cells, also of ectodermal origin, become part of the forgut and are derived independently from cells immediately behind the cephalic furrow.

The anterior endodermal anlage invaginates during gastrulation (stage 7) [Images] to produce the anterior midgut primordium, while the posterior midgut primordia sink into the embryo during stage 8 and enter the first postblastodermal division during stage 9. The anlagen for the hindgut form a ring encircling the posterior midgut primordia at the posterior pole. The whole of the hindgut is ectodermal in origin, including Malpighian tubules that form close to the junction between hindgut and posterior midgut.

The entire gut is remodeled during metamorphosis from imaginal cells at the base of the salivary glands (foregut), at the junction of the foregut and midgut, and in the hindgut and around the anus. Malpighian tubules are an exception to this remodeling process. Instead, they persist throughout metamorphosis unmodified.

Genes affecting ectodermal portions of the gut

Foregut is determined by the same genes that act in the gnathal (mouth) segments of head. Foregut is really an extention of mandible, maxillary and labial segments and is regulated by genes that are expressed in these segments including spalt, the head gap genes, and the ANTP-complex genes Deformed and Sex combs reduced.

Why is it that labial, the most anteriorly expressed ANTP-C gene, is not involved in foregut determination? The portion of the blastoderm that invaginates to form ectodermal gut derivatives is really ventral-anterior, resulting in the incorporation of cells of the gnathal segments into the forgut. The more dorsal anterior portions, including the pregnathal intercalary segment (expressing labial) form dorsal anterior structures such as the eyes and brain. tailless and forkhead are required for hindgut, including Malpighian tubules and anal plate, while huckebein is required for foregut only.

Reference

Skaer, H. (1993). The Alimentary Canal. pp 941-1012. In "The Development of Drosophila melanogaster." Eds. M. Bate and A. Martinez Arias. Cold Spring Harbor Laboratory Press.

date revised: 9 may 96 

Genes involved in organ development

Home page: The Interactive Fly © 1995, 1996 Thomas B. Brody, Ph.D.

The Interactive Fly resides on the
Society for Developmental Biology's Web server.