A glial cell arises from an additional division within the mechanosensory lineage during development of the microchaete on the Drosophila notum.

We have used different cell markers to trace the development of the sensory cells of the thoracic microchaete. Our results dictate a revision in the currently accepted model for cell lineage within the mechanosensory bristle. The sensory organ progenitor divides to form two secondary progenitors: PIIa and PIIb. PIIb divides first to give rise to a tertiary progenitor-PIII and a glial cell. This is followed by division of PIIa to form the shaft and socket cells as described before. PIII expresses high levels of Elav and low levels of Prospero and divides to produce neuron and sheath. Its sibling cell expresses low Elav and high Prospero and is recognized by the glial marker, Repo. This cell migrates away from the other cells of the lineage following differentiation. The proposed modification in lineage has important implications for previous studies on sibling cell fate choice and cell fate specification in sensory systems.