The Hox Gene, abdominal-A , controls the size and timely mitotic entry of neural stem cells during CNS patterning in Drosophila

Cell size is strongly correlated with several biological processes, including the cell cycle and growth. Here, we investigated the regulation of stem cell size during Drosophila central nervous system (CNS) development and its association with cell fate. We note that neural stem cells (NSC) in different regions of the ventral nerve cord increase their size at different rates. Thoracic NSCs grow at a faster rate compared with those in the abdominal region during larval development. We show that in addition to the known role in apoptosis and nervous system remodeling, larval expression of abdA is crucial in regulating the rate of postembryonic NSCs size increase, their timely exit from G ₂ phase and mitotic rate. We demonstrate that when abdA expression is lost in abdominal NSCs, their size increases, they exhibit a shorter G ₂ phase, enter mitosis earlier, and divide more rapidly. Conversely, the introduction of abdA in thoracic NSCs slows their growth and delays their entry into mitosis. We demonstrate that abdA-mediated NSC size regulation acts downstream of their nutrition-induced activation, thereby fine-tuning the stem cell potential spatiotemporally. This study highlights the instructive role of abdA in regulating various fates of larval NSCs during CNS patterning.