Abstract
The equilibrium between cell divisions that maintains stem cell fates and terminal cell divisions in which daughter cells adopt post-mitotic fates is essential to assure the correct number of determined cells at a given time at a given place. Here, we show that Tramtrack-69 (Ttk69, a BTB-ZF transcription factor ortholog of the human PLZF factor) plays an essential role in controlling the balance between cell proliferation and cell fate determination. In the Drosophila bristle cell lineage, we show that Ttk69 (1) promotes cell-cycle exit by downregulating the expression of cycE, the cyclin involved in S-phase entry, and (2) regulates terminal cell fate acquisition by downregulating that of hamlet and upregulating that of Suppressor of Hairless, two transcription factors involved in neural-fate acquisition and accessory-cell differentiation, respectively. Thus, Ttk69 plays a central role in shaping neural cell lineages by integrating molecular mechanisms that regulate progenitor cell-cycle exit and cell-fate commitment.