MORPHOLOGICAL ANALYSIS OF LARVAL DROSOPHILA ASTROCYTES IN THE VNC

Abstract

Understanding the ongoing signaling between neurons and glial cells requires a detailed analysis of glial cell morphology and physiology. In particular, the shapes and distribution of glial cells help to dictate roles astrocytes play in regulating neuronal function. In each segment of the ventral nerve cord of Drosophila, the neuropil is organized into distinct motor, interneuron, and sensory neuropils. Each hemisegment of the neuropil is served by six astrocytes, with somas in characteristic positions around the edge of neuropil. Here we use Flp-out (Ito et al., 1997) and MultiColor FlpOut (Viswanathan et al., 2015) genetic constructs targeted to astrocytes via the alrm-GAL4 driver (Doherty et al., 2009) to generate high-resolution images of astrocytes. Our examination of individual astrocytes, and the interfaces between adjacent astrocytes has revealed that (1) astrocytes have three morphological classes along with the identification of features such as wrapping/following FasII-positive axon bundles, midline crossing, single protruding processes, and a process leaving the CNS via the segmental nerve astrocytes display, (2) the arbors of individual astrocytes span multiple functional neural domains and (3) astrocytic branches have convoluted spatial domains, in which the finest distal branches of adjacent astrocytes interweave with a variable, but small, amount of interdigitation.