Analysis of the neurogenesis: Prepattern gene network controlling first stage of bristle pattern development in Drosophila melanogaster

The insect chitinous cover is not able to respond to stimuli and specialized receptors serve for them as environmental signal receivers. The drosophila perceives tactile stimuli by external sensor organs (microand macrochaetae) located on the head and back (notum). The microchaetae are numerous and generate regular rows oriented along the body. The number of macrochaetae is relatively small, and their location on the head and notum is strictly determined. Macrochaetae function as mechanoreceptors maintaining the balance in flight for a fly. The set of macrochaetae is called a bristle pattern. The full bristle pattern in the adult Drosophila melanogaster develops as a result of a multistage process. Its fundamental stage consists in the creation of a prototype of the future location of macrochaeta (prepattern presented by proneural clusters). The proneural clusters are separated from the mass of the wings’ imaginal disc cells at the stage of the third instar larvae and early prepupa under the influence of the prepattern factors identified with the transcription factors that directly regulate the expression of its target genes in the appropriate regions. The results of the reconstruction and analysis of the gene network, which provides the process of the prepattern formation, are for the first time given in the article; the principles of its organization and functioning are considered. The network includes 80 objects connected by 109 regulatory interactions. The proneural ASC proteins encoded by the achaete and scute genes, as well as the Decapentaplegic (Dpp) and Wingless (Wg) proteins, are the key objects of the network demonstrating the largest connectivity with its other components. The network structure is characterized by a hierarchic organization and has at least three management levels. The net functioning as an ensemble of the genes is achieved in general by the coordinated work of the regulatory circuits performing both the intra- and interlevel control for the gene activity. The resulting network effect consists in the activation of proneural AS-C complex genes, whose expression distinguishes the proneural cluster cells from the surrounding ectoderm cells.