ALTERNATIVE CELL FATE CHOICE INDUCED BY LOW-LEVEL EXPRESSION OF A REGULATOR OF PROTEIN PHOSPHATASE 2A IN THE DROSOPHILA PERIPHERAL NERVOUS-SYSTEM

The Drosophila gene twins encodes the regulatory B subunit of type 2A protein phosphatase. Here we report that its partial loss-of-function mutations caused abnormal morphogenesis in the adult peripheral nervou s system. In wild-type flies, the mechanoreceptor, one major class of sensory organs, is composed of four specialized cells (one neuron and three accessory cells) that are derived from a single precursor cell. The hypomorphic twins mutations did not block division of this precurs or, but most likely altered cell fate in this lineage to produce only accessory cells that form sensory structures. Stepwise reductions of t wins protein enhanced this transformation. In these mutants, another r egulatory subunit, A, and the catalytic subunit, C, of the phosphatase were expressed at normal levels. Therefore, the modulation of the pho sphatase activity by the B subunit appears to be crucial for specifica tion of neural cell identity.