The localization of chitin synthase mediates the patterned deposition of chitin in developing Drosophila bristles

The insect exoskeleton is a complex structure that is a key for the life style of this very successful group of animals. It contains proteins, lipids and the N-acetyl glucosamine polymer chitin. Chitin is synthesized by the enzyme chitin synthase. In most body regions, chitin fibrils are found in a stack of parallel arrays that can be detected by transmission electron microscopy. Each array is rotated with respect to the layers above and below. In sensory bristles, chitin primarily accumulates in bands parallel to the proximal/distal axis of the bristle. These bands are visible by confocal microscopy providing experimental advantages. We have used this cell type and an edited chitin synthase gene to establish that the bands of chitin are closely associated with stripes of chitin synthase, arguing the localization of chitin synthase plays an important role in mediating the patterned deposition of chitin. This is reminiscent of what has been seen for chitin and chitin synthase in fungi and between cellulose and cellulose synthase in plants. Several genes are known to be essential for proper chitin deposition. We found one of these, Rab11 is required for the insertion of chitin synthase into the plasma membrane and a second, duskylike is required for plasma membrane chitin synthase to localize properly into stripes. We also established that the actin cytoskeleton is required for the proper localization of chitin synthase and chitin in developing sensory bristles.