The Drosophila surface glia transcriptome: insights into conserved blood-brain barrier physiologies

Maintenance of central nervous system (CNS) homeostasis requires tight regulation over the metabolites, drugs, cells, and pathogens entering the brain. The blood-brain barrier (BBB) carries out these functions, but the regulatory mechanisms underlying BBB physiology are not completely understood. In addition, the BBB has long been an obstacle to the pharmacologic treatment of CNS diseases, thus molecular model systems that can parse BBB functions and understand the complex integration of sophisticated cellular anatomy and highly polarized chemical protection physiology are desperately needed. In this study, we developed FACS isolation methods for the purification of the surface glia that form the Drosophila BBB. By comparing the transcriptomes (via microarray analyses) of surface glia, FACS isolated neurons, and whole brains, we present a complete catalog of transcripts enriched at the Drosophila BBB. The surface glia transcriptome contains many ABC and SLC transporters, cell adhesion molecules, xenobiotic metabolism pathways, metabolic enzymes, and signaling molecules. Using gene set enrichment analyses and sequence-based comparisons, we compare the Drosophila surface glia to the vertebrate vascular endothelial BBB. Each replicate for the microarray analysis represented sorted cells originating from different growth bottles and processed on different days. Five total replicates were run for each of the following genotypes: wildtype whole brain, and sorted GFP positive cells from Repo, Elav, and 9-137.