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Drosophila Schneider 2 (S2) cells have been available for approximately 40 years. Their use has intensified over the past 15 years: resolution of the whole Drosophila melanogaster genome and the amenability of S2 cells for siRNA-based studies are some of the reasons for their growing use. This review covers recent publications on use of S2 cells for research and manufacturing and points to some possible future developments in their use in the vaccine field. Relatively few groups have systematically developed the system to enable expression of challenging proteins. They demonstrated that these cells can constitute a robust, efficient protein expression system, with specific advantages such as homogeneous glycosylation profile; reproducibility between production runs; options for cultivation modes, including perfusion; and no cell lysis, leading to relatively low levels of contaminating host cell proteins. The platform has shown to be particularly well adapted for the production of challenging viral, malaria and immunotherapy antigens.

The promoterless maize ubiquitin first exon and intron fragment can drive gusA expression in immature tritordeum inflorescences and immature wheat scutella. In fluorescence assays, this fragment induces gusA expression in tritordeum inflorescences to 50 times higher than background. The activity of the complete promoter, exon and intron cassette was up to 20 000-fold higher than background but the maize ubiquitin promoter in isolation had very low activity. A construct with the maize alcohol dehydrogenase first exon and intron had low activity, visible in histochemical assays. Both intron sequences have promoter-like features and in the ubiquitin intron there is a sequence homologous to the opaque-2-binding box. We suggest that the combination of these elements may explain the promoter activity detected in these introns.