Neuronal connectivity in the larval visual system of Drosophila melanogaster: Cellular and molecular analyses

Abstract

<p>In this study the Drosophila melanogaster larval visual system development was used as a model to identify cellular interactions and uncover molecular mechanisms that govern the formation of precise neuronal pathways during nervous system development. The first part of this study demonstrates that the outgrowth of two serotonergic processes and their contact with the larval optic nerve at the larval visual center are dependent on the proper development of larval optic nerve (LON). The second part of this study reports identification of molecular interactions that may be important for larval visual system development. A tissue-specific autoregulatory activity of a putative transcription factor DISCONNECTED (DISCO) has been shown to be important for proper larval visual system connectivity formation. To understand the molecular mechanisms that govern disco function in the visual system, two new proteins (DIP1 and DIP2; DISCO-interacting proteins 1 and 2) and a previously known protein that interact with DISCO in yeast and in vitro were identified. These proteins also show overlapping mRNA expression patterns with DISCO during embryogenesis. This study has also led to the identification of a putative activation domain in the DISCO protein. Furthermore, the results of this study suggest a possible protein-binding function of the second zinc-finger domain of DISCO. The dip1 gene encodes a protein with two putative dsRNA-binding motifs. An unusual repeated element is present in the 3' untranslated region of dip1 cDNAs. Northern analysis revealed expression of three different size transcripts of the gene during embryogenesis. The genetic location of the dip1 gene is similar to that of a gene called flamenco . The dip2 gene located at the polytene chromosome band 61B, codes for a highly conserved protein with presently unknown function. The amino acid sequence and mRNA expression pattern of the Drosophila DIP2 protein are very similar to its mouse homolog. This study contributes towards understanding the cellular and molecular mechanisms of neuronal connectivity formation.</p>