Neurons and glia in the midline of the higher crustacean Orchestia cavimana are generated via an invariant cell lineage that comprises a median neuroblast and glial progenitors

Midline cells are a common feature of both insects and crustaceans. Midline cells in the insects Schistocerca americana and Drosophila melanogaster ha ve been shown to give rise to pairs of either neurons or glial cells (midli ne precursor) as well as to repeatedly generate neurons (median neuroblast) or both neurons and glia (median neuroglioblast). This study addresses mid line cell lineages in a higher crustacean, the amphipod Orchestia cavimana. In vivo labeling of single midline cells shows that the resulting cell lin eage is invariant and that these cells act as progenitors for sets of three glial precursors and one median neuroblast. The progeny are restricted to parasegmental units. The glial precursors give rise to three pairs of glial cells; two of them enwrap the commissures. The median neuroblast gives ris e to about 10 cells that differentiate into 3 classes of neurons. The prese nce of median neuroblasts is also shown for another higher crustacean, the isopod Porcellio scaber using BrdU labeling. This is the first study to ana lyze the cell lineage of crustacean neurons generated by early ectodermal p recursors. A comparison with those of insects demonstrates both conservatio n and change during the evolution of arthropods. (C) 2001 Academic Press.