Developmental dynamics of peripheral glia in Drosophila melanogaster.

To study the roles of peripheral glia in nervous system development, a thorough characterization of wild type glial development must first be performed. We present a developmental profile of peripheral glia in Drosophila melanogaster that includes glial genesis, developmental morphology, the establishment of transient cellular contacts, migration patterns, and the extent of nerve wrapping in the embryonic and larval stages. In early embryonic development, immature peripheral glia that are born in the CNS seem to be intermediate targets for neurites that are migrating into the periphery. During migration to the PNS, peripheral glia follow the routes of pioneer neurons. The glia preferentially adhere to sensory axonal projections, extending cytoplasmic processes along them such that by the end of embryogenesis peripheral glial coverage of the sensory system is complete. In contrast, significant lengths of motor branch termini are unsheathed in the mature embryo. During larval stages however, peripheral glia further extend and elaborate their cytoplasmic processes until they often reach to the neuromuscular junction. Throughout the embryonic and larval developmental stages, we have also observed a number of similarities of peripheral glia to vertebrate Schwann cells and astrocytes. Peripheral glia seem to have dynamic and diverse roles and their similarities to vertebrate glia suggest that Drosophila may serve as a powerful tool for analysis of glial roles in PNS development in the future.