Dynamics of Adult Neurogenesis in Interspecies Brain Chimeras

Adult neurogenesis is a dynamically regulated process where new neurons are generated from neural stem cells (NSCs) in the adult brain of mammals 1. This process is tightly regulated by the intrinsic properties of the stem cells and the extrinsic factors in the microenvironment surrounding them, i.e., the niche 2. However, dynamics of the interplay between extrinsic and intrinsic factors determining the behavior of neural stem cells remains largely unknown. In particular, the possible role of the extrinsic factors provided by the neurogenic niche as the possible driving force of neurogenic divisions is surprisingly under investigated. This is becomes even more important in the context of the regenerative medicine and organ transplants where the influence of the host environment of the recipient tissue is important in determining the outcome. Here, we aim to investigate the interaction of the two using interspecies rat-mouse chimeras where rat cells will be transplanted in a mouse niche. To study the effect of the niche on the behavior of resident stem cells, we will investigate the following activity of rat cells that have been shown to be different from mice: the speed of differentiation, the rate of cell death, density of new-born neurons and expression of specific markers. We will generate rat-mouse chimeras where rat pluripotent cells (PSCs), labelled Kusabira Orange (KsO), are injected in a mouse blastocyst, resulting in a mouse with significant contributions from rat cells. Using EdU injections in 6-week old rat-mouse chimeras to label the dividing cell, we will then sacrifice the mice at three timepoints post injection: 3 days, 7 days and 14 days. We will then study if the mouse niche affects the characteristic behavior of the rat NSCs. The hypothesis that the extrinsic factor determines the activity of NSCs will be assumed if the rat NSCs alter their activity to match that of the resident mouse NSCs. Following this, we will then aim to increase adult neurogenesis by affecting the neurogenic niche in the mouse hippocampus by inducing a controlled cortical impact injury 3. To determine the effect of the changes in signaling from the niche on rat and mouse NSCs, we will perform immunohistochemistry to study the rate of neurogenesis, electrophysiological studies to determine the integration of new-born rat neurons and single-cell RNA sequencing to untangle the molecular changes in the rat NSCs. In the end, this projects aims to provide a comprehensive understanding of the effect of niche on the potential of resident stem cells. Knowledge about the impact of niche signalling on stem cells will allow important insights that might be relevant for many related fields such as reprogramming, brain repair and regeneration and aging.