Novel actin rings within the secretory cells of honeybee royal jelly glands.

We describe a novel cytoskeletal element within secretory cells of an arthropod gland system, the hypopharyngeal gland of the honeybee, Apis mellifera. The hypopharyngeal secretory cells are the source of royal jelly in nurse bees and enzymes in foragers. Each cell possesses an elongate invagination that is occupied by a tubular cuticular structure, the end-apparatus, that accumulates secretion and transfers it into a cuticular microtube and then into a collecting duct. Within the secretory cell, a conspicuous series of actin rings, about 3 μm in diameter, follows the same path as the end-apparatus, surrounding it at spaced intervals. Transmission electron microscopy confirmed that the actin rings lie within septa of the secretory cell that are closely juxtaposed to the end-apparatus at regularly spaced intervals. We speculate that the function of the actin rings is to hold the end apparatus in place as secretion swells the extracellular compartments between the end apparatus and the cell membrane. To our knowledge, no such cytoskeletal component has been described in animal cells. © 2012 Wiley Periodicals, Inc.