Sibling cell fate in the Drosophila adult external sense organ lineage is specified by Prospero function, which is regulated by Numb and Notch

Specification of cell fate in the adult sensory organs is known to be depen dent an intrinsic and extrinsic signals. We show that the homeodomain trans cription factor Prospero (Pros) acts as an intrinsic signal for the specifi cation of cell fates within the mechanosensory lineage. The sensory organ p recursors divide to give rise to two secondary progenitors - PIIa and PIIb Pros is expressed in PIIb, which gives rise to the neuron and thecogen cell s. Loss of Pros function affects the identity of PIIb and neurons fail to d ifferentiate. Pros misexpression is sufficient for the transformation of PI Ia to PIIb fate. The expression of Pros in the normal PIIb cell appears to be regulated by Notch signaling.