The Interactive Fly
Genes involved in tissue and organ development
The stomatogastric nervous system (SNS) consists of several peripheral ganglia that receive input from the brain; these ganglia in turn innervate muscles, pharynx, and gut. Precursors originate from the primordium of the foregut or stomodeum [Images]. The SNS is considered to be derived from the labral segment, the most anterior of the head segments. Early in development several subsets of precursors delaminate from the stomodeal epithelium as individual cells.
Three cells are singled out from within a single proneural cluster, known as the SNS anlage; these cells then initiate a distinct feature of SNS development. Serving as tip cells, they direct a second phase of SNS development wherein an invagination process occurs, forming three distinct epithelial folds with a single proneural-expressing cell at each tip. achaete-scute and neurogenic genes function here in the same manner as they do in the development of the ventral nerve cord, except that three cells are selected, not just one. The homeobox protein Goosecoid marks cells fated to become SNS cells.
Once the invagination process is complete, proneural gene expression appears de novo in all cells contained within the three invaginations; the three invaginations then pinch off from the epithelium to form separate epithelial vesicles. At later stages the cells of the three vesicles migrate to various locations where they differentiate as neurons, organizing into the mature embryonic SNS. Subsequently, these neural cells generate the axonal scaffold. Neurons from the individual ganglia send out pioneer axons that meet up with outgrowing axons from the other ganglia and eventually establish the interconnecting nerves. Other neurons send out axons to establish the nerves that innervate the dorsal pharyngeal muscles, the midgut and the CNS.
The mature embryonic SNS consists of only four ganglia (the frontal ganglion, the esophageal ganglion 1, the esophageal ganglion 2, and the proventricular ganglion) and their associated nerve tracts. The glia of the mature SNS are found as three groups of cells: one group is associated with the frontal ganglion (the frontal ganglion glia), a second group is found in the frontal commissure, at the base of the frontal nerve (commisural glia), and a third group is located at the fork in the recurrent nerve, off of which the two esophageal ganglia extend (esophageal ganglia glia).
Forjanic, J. P., et al. (1997). Genetic analysis of stomatogastric nervous system development in Drosophila using enhancer trap lines. Development 186: 139-154.
González-Gaitan, M. and Jäckle, H. (1995). Invagination centers within the Drosophila stomatogastric nervous system anlage are positioned by Notch-mediated signaling which is spatially controlled through wingless. Development 121: 2313-25
Goriely, A., et al. (1996). A functional homologue of goosecoid in Drosophila. Development 122: 1641-1650
Hartenstein, V., Tepass, U. and Gruszynski-deFeo, E. (1996). Proneural and neurogenic genes control specification and morphogenesis of stomatogastric nerve cell precursors in Drosophila Dev. Biol. 173: 213-227
Schmidt-Ott, et al. (1994). Number, identity, and sequence of the Drosophila head segments as revealed by neural elements and their deletion patterns in mutants. Proc. Natl. Acad. Sci. 91: 8363-8367
Genes involved in organ development
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