The adult Drosophila salivary gland exhibits an unusual mode of cell division
Authors: Caitlin van Ree; Nicole Dominado; Nicole Siddall; Gary Hime
Affiliation: Department of Anatomy and Physiology, University of Melbourne, Parkville, VIC , Australia
Keywords: o. tissue growth and remodeling; q. developmental modulation
Larval salivary glands of Drosophila are well known to exhibit polytene salivary glands formed via endoreplication and have been long used to study this process. In contrast, less is known of the development of adult Drosophila salivary glands except that they consist of a single layer, tubular epithelium that originates from a population of diploid cells found as an imaginal ring near larval salivary gland ducts. We have shown that the adult salivary glands contain three distinct epithelial domains, two of which are comprised of cuboidal epithelial cells and one of squamous epithelial cells. These cell types develop during the pupal period and after eclosion secretory cells develop extensive apical membrane invaginations. The junctional polarity of the epithelial cells exhibits an unusual change soon after eclosion as E-cadherin localisation migrates from a position apical to the septate junction to a more basal position. The epithelial cells are polyploid and larger than the imaginal ring cells from which they derive. The adult salivary epithelial cells do not undergo mitosis as they do not express phosphorylated Histone H3, yet total cell numbers increase within 2 days of eclosion. By using genetic tools designed for the MARCM lineage tracing technique we have shown that the polyploid cells of the cuboidal epithelium lose chromosomes during the division period and appear to be using amitosis as a mechanism to increase cell number. Amitosis is a form of cell division undertaken by polyploid cells that does not require establishment of a mitotic spindle and results in chromosome loss. Amitosis may be an unusual mechanism to be utilised in primary formation of a tissue but it may be the only efficent way for polyploid cells to increase in number. The adult Drosophila salivary gland will serve as a model for genetic analysis of this mode of division.