Distribution, classification, and development ofDrosophila glial cells in the late embryonic and early larval ventral nerve cord

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Abstract
To facilitate the investigation of glial development inDrosophila, we present a detailed description of theDrosophila glial cells in the ventral nerve cord. A GAL4 enhancer-trap screen for glial-specific expression was performed. Using UAS-lacZ and UAS-kinesin-lacZ as reporter constructs, we describe the distribution and morphology of the identified glial cells in the fully differentiated ventral nerve cord of first-instar larvae just after hatching. The three-dimensional structure of the glial network was reconstructed using a computer. Using the strains with consistent GAL4 expression during late embryogenesis, we traced back the development of the identified cells to provide a glial map at embryonic stage 16. We identify typically 60 (54–64) glial cells per abdominal neuromere both in embryos and early larvae. They are divided into six subtypes under three categories: surface-associated glia (16–18 subperineurial glial cells and 6–8 channel glial cells), cortex-associated glia (6–8 cell body glial cells), and neuropile-associated glia (8–10 nerve root glial cells, 14–16 interface glial cells, and 3–4 midline glial cells). The proposed glial classification system is discussed in comparison with previous insect glial classifications.