| A central question in developmental biology is how different cells and tissues commit and determine their fates. To better answer this question, I studied the function of Pax6 and Polycomb group (PcG) proteins in the eye-antennal disc of Drosophila, the fruitfly. The eye-antennal disc gives rise to most of the fruitfly head structures, including the compound eye, ocelli, antenna, maxillary pulps and the surrounding head epidermis. Previous research showed that the development of each different head structure, for example, the eye or the antenna, is regulated by its distinct gene regulatory network (GRN). However, in my dissertation, I found that the key regulatory gene of eye development, Pax6, promotes the entire eye-antennal disc development at early stages. Loss of Pax6 results in headless pharate adults, which flies lack all head structures derived from the eye-antennal disc. I show that Pax6 controls cell proliferation of early head development via several retina genes, indicating that the retina gene network is responsible for promoting head development at early eye-antennal disc development before its role shifts to promote eye development at later development. I also demonstrated how epigenetics plays roles in maintaining the eye fate. I show that when PcG proteins, the epigenetic silencers, are removed from the early eye development, the eye disc transforms into a wing disc, causing formation of ectopic wings on fly heads. But at later stage when eye progenitor cells already committed to their fate, PcG activity is no longer required to suppress wing fate. These findings indicate a loss of tissue plasticity when development proceeds. In summary, I described the dynamic requirements of Pax6 and PcG proteins at different developmental stages of the eye-antennal disc. Their activities are essential for proper formation of Drosophila head structures. |
