Development of astrocyte-like and ensheathing glia of the early larva ventral nerve cord. Emilie Peco¹, Sejal Davla¹, Stephanie Stacey¹, Matthias Landgraf², Don van Meyel¹. 1) Centre for Research in Neuroscience, McGill University, Montreal, Qc, Canada; 2) Department of Zoology, University of Cambridge, UK.

   CNS glia in mammals and invertebrates are of heterogeneous subtypes serving diverse and specialized functions. However, knowledge of the extent of glial diversity and how it arises during development is quite limited. The aim of our study was to explore diversity among neuropil-associated glia of the Drosophila ventral nerve cord, and more precisely among Longitudinal Glia (LG) composed of 9 identifiable cells derived from a unique glioblast. In late embryos, LG can be divided into subtypes based on gene expression profiles, but little is known about their mature properties (morphology, physiology) and functions in larvae. We used the Blown-out recombination system to selectively label and identify each LG cell in L1 larvae, and precisely examined their morphology and organization. Interestingly, we found that LG comprise 3 distinct and stereotypic glial subtypes: astrocyte-like, ensheathing and nerve-associated glia. Time-lapse analysis of LG development from their origin to their mature state confirmed that these 3 subtypes derive from the same progenitor. What molecular mechanisms control the generation of distinct identities from a single progenitor? We found that Notch signaling, acting early in the lineage, controls alternative astrocyte-like and ensheathing glia fates. We also found that one effector of Notch in this process is the transcription factor Prospero. For each astrocyte-like glial cell, we then used landmarks positive for fasciclin 2 to map the positions of the cell bodies and the domains of the synaptic neuropil covered by their dense membranous processes. We found stereotypy with which they selectively associate with particular regions of the neuropil. Together, these results document a previously undiscovered pattern of differentiation, migration, and morphogenesis among CNS glia, setting the stage for future work to discover additional cellular and molecular mechanisms leading to diversification of form and function among CNS glia.