ABSTRACT
The role of developmental cell death in the formation of brain circuits is not well understood. Cajal-Retzius cells constitute a major transient neuronal population in the mammalian neocortex, which largely disappears at the time of postnatal somatosensory maturation. In this study, we used mouse genetics, anatomical, functional, and behavioral approaches to explore the impact of the early postnatal death of Cajal-Retzius cells in the maturation of the cortical circuit. We find that before their death, Cajal-Retzius cells mainly receive inputs from layer 1 neurons, which can only develop their mature connectivity onto layer 2/3 pyramidal cells after Cajal-Retzius cells disappear. This developmental connectivity progression from layer 1 GABAergic to layer 2/3 pyramidal cells regulates sensory-driven inhibition within, and more so, across cortical columns. Here we show that Cajal-Retzius cell death prevention leads to layer 2/3 hyper-excitability, delayed learning and reduced performance in a multi-whisker-dependent texture discrimination task.
Subject(s)
Cell Death , Pyramidal Cells , Somatosensory Cortex , Animals , Somatosensory Cortex/physiology , Somatosensory Cortex/cytology , Mice , Pyramidal Cells/physiology , Pyramidal Cells/metabolism , Neocortex/cytology , Neocortex/physiology , GABAergic Neurons/physiology , GABAergic Neurons/metabolism , Male , Vibrissae/physiology , Female , Mice, Inbred C57BL , Neural Inhibition/physiology , Neurons/physiology , Neurons/metabolismABSTRACT
The Beautiful Brain is a documentary web series that breaks down borders between science and art. Five episodes retrace in a simple, but visually effective, way five key steps of brain development, using awe-inspiring masterpieces of art as analogies. This unconventional series focuses on fundamental research in neuroscience, the communication of which is not always easy and straightforward. In this article, we share our experience of how we tried to overcome the difficulties of communicating fundamental science to the lay audience. Moreover, we give insights into the path we followed to create The Beautiful Brain, with the hope that our experience may be an inspiration to other basic scientists who wish to communicate their own research.
Subject(s)
Brain , Science , CommunicationABSTRACT
We present a strategy for measuring the density of presynaptic boutons of superficial neuronal cells in the mouse neocortex. First, we show how to sparsely label individual postmitotic cells by neonatal pial-surface electroporation. Then, we present a custom-made code that allows quantification of the density of presynaptic boutons along axonal processes. Although we applied this strategy to somatostatin-positive cells, a major population of cortical interneurons, the same approach can be adjusted to target other types of neuronal cells. For complete details on the use and execution of this protocol, please refer to Gesuita et al. (2022).1.
Subject(s)
Neocortex , Mice , Animals , Synapses/physiology , Presynaptic Terminals/physiology , Axons/physiology , Neurons/physiologyABSTRACT
Microglia play a key role in shaping the formation and refinement of the excitatory network of the brain. However, less is known about whether and how they organize the development of distinct inhibitory networks. We find that microglia are essential for the proper development of somatostatin-positive (SST+) cell synapses during the second postnatal week. We further identify a pair of molecules that act antagonistically to one another in the organization of SST+ cell axonal elaboration. Whereas CX3CL1 acts to suppress axonal growth and complexity, CXCL12 promotes it. Assessing the functional importance of microglia in the development of cortical activity, we find that a whisker stimulation paradigm that drives SST+ cell activation leads to reduced cortical spiking in brains depleted of microglia. Collectively, our data demonstrate an important role of microglia in regulating the development of SST+ cell output early in life.
Subject(s)
Interneurons , Vibrissae , Animals , Interneurons/physiology , Microglia , Somatostatin , Synapses/physiologyABSTRACT
The development of neocortical layer 1 is a very dynamic process and the scene of multiple transient events, with Cajal-Retzius cell death being one of the most characteristic ones. Layer 1 is also the route of migration for a substantial number of GABAergic interneurons during embryogenesis and where some of which will ultimately remain in the adult. The two cell types, together with a diverse set of incoming axons and dendrites, create an early circuit that will dramatically change in structure and function in the adult cortex to give prominence to inhibition. Through the engagement of a diverse set of GABAergic inhibitory cells by bottom-up and top-down inputs, adult layer 1 becomes a powerful computational platform for the neocortex.
Subject(s)
Neocortex , Axons , InterneuronsABSTRACT
This protocol presents a plate-based workflow to perform RNA sequencing analysis of single cells/nuclei using Smart-seq2. We describe (1) the dissociation procedures for cell/nucleus isolation from the mouse brain and human organoids, (2) the flow sorting of single cells/nuclei into 384-well plates, and (3) the preparation of libraries following miniaturization of the Smart-seq2 protocol using a liquid-handling robot. This pipeline allows for the reliable, high-throughput, and cost-effective preparation of mouse and human samples for full-length deep single-cell/nucleus RNA sequencing. For complete details on the use and execution of this protocol, please refer to Bowers et al. (2020).
Subject(s)
Sequence Analysis, RNA/instrumentation , Single-Cell Analysis/instrumentation , Single-Cell Analysis/methods , Animals , Base Sequence/genetics , Brain/cytology , Brain/metabolism , Cell Nucleus/metabolism , Cell Separation/methods , Gene Expression/genetics , Gene Expression Profiling/methods , Gene Library , High-Throughput Nucleotide Sequencing/methods , Humans , Mice , Miniaturization , RNA/genetics , Sequence Analysis, RNA/methods , Transcriptome/genetics , Exome Sequencing/methods , WorkflowABSTRACT
Visual system development involves the formation of neuronal projections connecting the retina to the thalamic dorso-lateral geniculate nucleus (dLGN) and the thalamus to the visual cerebral cortex. Patients carrying mutations in the SOX2 transcription factor gene present severe visual defects, thought to be linked to SOX2 functions in the retina. We show that Sox2 is strongly expressed in mouse postmitotic thalamic projection neurons. Cre-mediated deletion of Sox2 in these neurons causes reduction of the dLGN, abnormal distribution of retino-thalamic and thalamo-cortical projections, and secondary defects in cortical patterning. Reduced expression, in mutants, of Sox2 target genes encoding ephrin-A5 and the serotonin transport molecules SERT and vMAT2 (important for establishment of thalamic connectivity) likely provides a molecular contribution to these defects. These findings unveil thalamic SOX2 function as a novel regulator of visual system development and a plausible additional cause of brain-linked genetic blindness in humans.