The generation of neurons in the mammalian brain involves a highly complex but carefully choreographed sequence of events including the regulated proliferation of neural progenitor cells, their carefully-timed differentiation into neurons, the migration of newly produced neurons to predictable destinations in the brain, the extension of axons that connect to target cells sometimes located at a considerable distance away and the life-long maintenance of survival of mature neurons that have made proper connections. Numerous molecules have been identified that are involved in the control of these processes. Among these, TLE1, FoxG1, and MeCP2 play critical roles on early brain development. Whereas TLE1 and FoxG1 ensure that neural progenitor cells continue to proliferate until proper brain mass is built, MeCP2 has been implicated in the regulation of various developmental process including survival of neural progenitor cells, axon guidance and morphogenesis of certain brain parts. However, all three of these molecules are abundantly expressed in neurons of the postnatal brain and into adulthood. Their roles in postmitotic neurons are poorly understood. The research I have done as part of my thesis and described herein has shed light on this important issue. I have discovered that FoxG1 and TLE1 cooperate to maintain the survival of postmitotic neurons. In contrast, one of the two isoforms of MeCP2 promotes neuronal death. I discovered that FoxG1 inhibits this cell death-promoting activity of MeCP2. I believe my research provides new information on how the survival of neurons is maintained normally. It is possible that deregulation of these molecules contributes to the abnormal loss of neurons in neurodegenerative diseases as well as to dysfunction of neurons in other brain disorders. Indeed mutations of MeCP2 and FoxG1 cause Rett syndrome, a debilitating neurodevelopmental disorder. The dissertation is organized into four chapters. Chapter 1 provides an introduction of TLE1, FoxG1 and MeCP2 whereas the other three chapters describe my research on each of the three molecules and the interrelationships between them.