(64a) Extrinsic Growth Signals Driving Drosophila Imaginal Cell Proliferation In Vitro

Insect cell lines are used both commercially in the production of heterologous recombinant proteins and as biochemical tools that complement research in established genetics systems such as Drosophila embryonic and larval development. Recently, a few studies have been successful in identifying novel extrinsic growth factors that stimulate the growth of a cell line, Cl.8, which was derived from wing imaginal disks. The utility of Cl.8 cells for growth control research derives from their strong dependency on growth factors to proliferate. Motivated by the success of previous studies and recognizing that much is still unknown about extrinsic regulators of insect growth, we have undertaken a detailed characterization of the culture medium supporting proliferation of Cl.8 cells. Our approach has been to use design-of-experiment methodology to screen conditions and optimize the current culture medium to gain further insight into extrinsic growth regulation of imaginal cells. We have found that of three supplements included in the original media formulation, a raw extract derived from Drosophila was the only essential factor. As a result we have optimized the extraction process to improve the stimulatory effect and are characterizing the biochemical properties of components from the extracts, which affect both proliferation and cell-cell adhesion. Efforts to formulate a more defined culture medium for Cl.8 cells will further increase the utility of this cell-line in Drosophila genetics studies on growth control. The identification of novel growth factors stimulating Cl.8 cells also has the potential to inform efforts toward increasing the yield of insect cells in commercial applications.