TRAMTRACK ACTS DOWNSTREAM OF NUMB TO SPECIFY DISTINCT DAUGHTER CELL FATES DURING ASYMMETRIC CELL DIVISIONS IN THE DROSOPHILA PNS

Asymmetric eel divisions allow a sensory organ precursor (SOP) cell to generate a neuron and its support cells in the Drosophila PNS. We dem onstrate a role of tramtrack (ttk), previously identified as a zinc fi nger-containing putative transcription factor, in the determination of different daughter cell fates. Both loss of function and overexpressi on of ttk affect the fates of the SOP progeny. Whereas loss of ttk fun ction transforms support cells to neurons, ttk overexpression results in the reverse transformation. ttk is expressed in support cells but n ot in neurons. It has been shown that numb, a membrane-associated prot ein asymmetrically distributed during the SOP division, confers differ ent daughter cell fates. Loss of ttk or numb function results in recip rocal cell fate transformation. Epistatic studies suggest that ttk act s downstream of numb. We propose that ttk executes the command dictate d by asymmetrically localized numb to specify distinct daughter cell f ates during multiple asymmetric divisions.