Fig. 1. Profile of peripheral glial actin-GFP during wild-type embryonic development. repo::actin-GFP embryos were fixed and stained with anti-GFP, then viewed with laser scanning confocal microscopy. Anterior is towards the top, CNS is to the left of vertical broken lines. For a detailed characterization of wild-type glial migration in relation to motor and sensory neurons, see also Sepp et al. (Sepp et al., 2000). (A) Stage 12. Peripheral glia arise and proliferate at the lateral edge of the CNS (arrows). At this early stage, they are compact, and the glial cluster forms a cone shaped array in each hemisegment. (B) Stage 13. The peripheral glia begin to migrate into the periphery. The leading glial cells extend small actin-filled projections (concave arrow). (C) Stage 14. As the leading glia move further peripherally, their cell bodies (nuclei are oval shaped and lacking actin-GFP staining) can travel just behind the leading cytoplasmic edge (solid arrow). Alternatively, the cell body can be found on the trailing region of the cell, while a long process with lamellar-like structures (arrowhead) can be found at the leading edge. Filopodia-like protrusions extend from the leading glial cells in each hemisegment (concave arrows). (D) Stage 15. The phase of glial migration is almost complete. The ventral peripheral glia (vPG, solid arrow), which initially migrates in the cone-shaped glial cluster, separates its processes from the other glia to ensheathe the ventral cluster sensory neurons. The lateral chordotonal glia (concave arrow), lateral bipolar dendritic glia (asterisk) and the lateral line glia (arrowhead) arise from the periphery and are also labeled with actin-GFP. (E) Stage 16. In the mature embryo, the overall actin-GFP profile is smoother, with no visible spike-like protrusions as in the earlier migratory phase. The vPG cell has fully resolved from the main (anterior fascicle) nerve tract (arrow). The lateral chordotonal glia (concave arrow), which associate with the cell bodies of the lateral chordotonal neurons, are interconnected with the peripheral glia.

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