Periodic Reporting for period 3 - GIDE (Molecular diversification of inhibitory neurons during development)
Periodo di rendicontazione: 2022-01-01 al 2023-06-30
The central nervous system consists of diverse types of neurons and glia that vary widely in morphology, physiology, connectivity, molecular markers, and *in vivo* patterns of activity. During development, molecular diversity is initially reflected in the regional expression of a narrow set of transcription factors across mitotic progenitors. However, transcriptional signatures that distinguish mature neuronal subtypes emerge only after cell cycle exit and become more sharply defined during postnatal development. In this project, we explore the extent to which developmental trajectories are predetermined by specified progenitors during mitotic stages, or emerge through interactions with the environment later in development. We combine genetic fate-mapping with high-throughput single-cell RNA sequencing and molecular tagging strategies to gain a detailed understanding of neurogenesis at the cellular level. Furthermore, we study the genetic mechanisms that enable cell intrinsic programs to be shaped by environmental processes during postnatal development. A growing body of evidence suggests that perturbation of neuronal differentiation can result in a variety of complex neuropsychiatric disorders, including epilepsy, autism, bipolar disorder, and schizophrenia. Thus, elucidating how neuronal types emerge and integrate into brain circuits is crucial for understanding the brain in both health and disease.
During the reporting period, we developed two novel approaches to enable massive parallel tagging of progenitors to track clonal relationships and transcriptomic signatures during mouse forebrain development. Both methods are scalable and can be applied to any cell type in the brain without requiring a priori knowledge of the cells under investigation. We have used these methods to investigate whether the clonal divergence of GABAergic types is the result of a lineage-dependent process in which a mitotic progenitor generates different types of neurons, or whether lineage-independent mechanisms such as neuronal activity or cell migration control this process later during postnatal differentiation. We discovered an extensive degree of clonal divergence among different types of inhibitory neurons, with the surprising observation that distinct neuronal cell types in the cortex, striatum, olfactory bulb, and amygdala share a common lineage. Furthermore, we found that immediately after exiting the cell-cycle, GABAergic neurons originating from the same mitotic progenitor diverged into different trajectories, suggesting that differentiation into subtypes is initiated as a lineage-dependent processes at the progenitor cell level.
Clonal divergence, as we discovered in this project, could explain why somatic mutations can affect a wide range of different cell types and could explain why often different subsets of cells are affected in developmental disorders. By the end of the project, we expect to have more information on how these intrinsic programs derived from mitotic progenitor cells are shaped during postnatal development by environmental processes, and in particular neuronal activity.