Dorsal longitudinal stretch receptor of Drosophila melanogaster larva – Fine structure and maturation

Insects possess two types of sensory neurons: ciliated type I sensory neurons that innervate external sensory organs and chordotonal organs, and type II sensory neurons that form a subepidermal plexus or innervate stretch receptors. Among stretch receptors, a dorsel longitudinal stretch receptor is highly conserved in insects, being found in all insect orders investigated. Here we describe the topology and anatomical structure of this receptor in the fruit fly embryo and larva using transmission electron microscopy and single cell staining for fluorescence microscopy. The receptor is composed of the dorsal bipolar dendrite neuron, which arises from an archetypal cell lineage, its sister glial cell and the peripheral glial cell accompanying the nerve. The neuron is situated among the muscles in the dorsal body wall on the intersegmental nerve. Its two dendrites stretch the length of the segment to the segmental folds. The neuron is wrapped by both glial cells and surrounded by a common basal lamina, which fans out at the dendritic tips to attach them to the epidermal cells at the segmental borders.