Periodic Reporting for period 3 - NATURE_NURTURE (Intrinsic and extrinsic determinants of neuronal identity)
Reporting period: 2023-09-01 to 2025-02-28
Problem addressed: Neuronal diversity is key to understanding the variety of circuits in an animal's brain, which determines its behavior. However, determining how neuronal diversity arises from cell-intrinsic and cell-extrinsic processes is challenging because of the dynamic sensitivities of different neuron types to environmental signals. This complexity makes it difficult to parse out the respective contributions of intrinsic and extrinsic drivers of cell-type specification and differentiation in the central nervous system.
Overall objectives: The objective of this project is to determine core drivers of progenitor and neuron types through the identification of intrinsic and environmental drivers of cellular identity. We are achieving this by characterizing the emergence of area-specific neuronal and progenitor identities, the plasticity of area-specific neuronal states in response to genetic manipulation, the spatial context-independent components of neuron identity, and the postnatal experience-dependent controls over neuronal identity.
Importance for society: This research program will increase our knowledge of genetic programs and circuit-derived genetic programs by identifying key mechanisms and pathways of neuronal differentiation in response to environmental signals. This information could be used to develop targeted treatments for neurodevelopmental disorders and following injury. By providing greater insight into the relationship between genetic programs and behavior, we may be able to understand and develop better treatments for mental health disorders.
Overall objectives: The objective of this project is to determine core drivers of progenitor and neuron types through the identification of intrinsic and environmental drivers of cellular identity. We are achieving this by characterizing the emergence of area-specific neuronal and progenitor identities, the plasticity of area-specific neuronal states in response to genetic manipulation, the spatial context-independent components of neuron identity, and the postnatal experience-dependent controls over neuronal identity.
Importance for society: This research program will increase our knowledge of genetic programs and circuit-derived genetic programs by identifying key mechanisms and pathways of neuronal differentiation in response to environmental signals. This information could be used to develop targeted treatments for neurodevelopmental disorders and following injury. By providing greater insight into the relationship between genetic programs and behavior, we may be able to understand and develop better treatments for mental health disorders.
The first half of the research project is focused on understanding how area-specific molecular identities of progenitors and their daughter neurons emerge during embryonic and postnatal development. We found that spatial information is more prominent in progenitors at early developmental stages and that it is better encoded in emerging neuronal populations at later stages. We have also started the second part of the project, which involves manipulating area-specific neuronal identities in proof-of-principle areas using transplantation experiments. We have assessed the robustness of molecular identity of specific neuronal populations. In vitro circuits showed features that were reminiscent of the ones they have in vivo. We are now using organotypic cultures to confirm these findings. Lastly, we are investigating the role of postnatal sensory experience in acquiring neuronal identity in Acomys Dimidiatus, a precocial rodent, and have established the timing of cortical neurogenesis in this species.
Since the beginning of the project, significant progress has been made in understanding neuronal identity and cortical area specification. In WP1, we tracked the emergence of area-specific molecular identities in progenitors and neurons, analyzing single-nuclei RNA sequencing data and spatial gene expression. We identified molecular spatial patterns that are conserved across development, inherited from progenitors, or emerge during postmitotic maturation. In WP2, we performed transplantation experiments to manipulate neuronal identity, using Patch-seq to analyze molecular, morphological, and electrophysiological properties. We also performed environmental manipulations in vivo, demonstrating the remarkable stability of neuronal identity despite changes in positioning and innervation. In WP3, we assessed molecular identity robustness in vitro, showing that glutamatergic neurons lose identity-defining gene expression and diversity in 2D cultures but retain them in organotypic slices, highlighting the role of extracellular context. In WP4, we investigated postnatal sensory experience in neuronal identity acquisition, determining the timeline of upper-layer neurogenesis in Acomys dimidiatus. We conducted single-nuclei RNA sequencing analyses, revealing mosaic maturation of neuronal subtypes and cortical areas. Ongoing transcriptomic, histological, and electrophysiological studies aim to further characterize these findings. Overall, our work demonstrates the interplay between genetic and environmental factors in shaping neuronal identity and diversity.