Oenocyte development in the red flour beetle Tribolium castaneum.

Oenocytes are a specialized cell type required for lipid processing, pheromone secretion, and developmental signaling. Their development has been well characterized in Drosophila melanogaster, but it remains unknown whether the developmental program is conserved in other insect species. In this study, we compare and contrast the specification and development of larval oenocytes between Drosophila and the red flour beetle, Tribolium castaneum. First, we identify several useful reagents to label larval oenocytes, including both a Tribolium GFP enhancer trap line and a simple flurophore-conjugated streptavidin staining method that recognizes oenocytes across insect species. Second, we use these tools to describe oenocyte development in Tribolium embryos, and our findings provide evidence for conserved roles of MAP kinase signaling as well as the Spalt, Engrailed, hepatocyte nuclear factor-4, and ventral veins lacking factors in producing abdominal-specific oenocyte cells. However, Tribolium embryos produce four times as many oenocytes per abdominal segment as Drosophila, and unlike in Drosophila, these cells rapidly downregulate the expression of the Spalt transcription factor. Thus, these results provide new insight into the molecular pathways regulating oenocyte specification across insect species.