Project description:Mammalian brains vary in size, structure, and function, but the extent to which evolutionarily novel cell types contribute to this variation remains unresolved. Recent studies suggest there is a primate-specific population of striatal inhibitory interneurons, the TAC3 interneurons. However, broader taxonomic and developmental characterization is required to address novelty in cell type evolution. Here, we examine gene expression in inhibitory neurons across 11 mammalian species, spanning 160 million years divergence from primates. We find that the initial class of newborn TAC3 interneurons specified during development represents an ancestral, MGE-derived striatal population also present in pig and ferret cortex. This discovery prompted a reexamination of the Glire clade, including mice which are thought to lack the TAC3 type. Targeted enrichment of MGE precursors in mice reveals conservation of the TAC3 initial class, camouflaged by reduced expression of Tac2 (the mouse ortholog of TAC3) and a gain of Th expression. Extending our analysis to the adult striatum further supports the homology of primate TAC3 and mouse Th striatal interneurons, while uncovering a rare Tac2 subpopulation in mouse ventromedial striatum. This study suggests that initial classes of telencephalic inhibitory neurons are largely conserved and that during evolution, neuronal types in the mammalian brain change through redistribution and fate refinement, rather than by derivation of novel precursors early in development.
Project description:Mammalian brains vary in size, structure, and function, but the extent to which evolutionarily novel cell types contribute to this variation remains unresolved1-4. Recent studies suggest there is a primate-specific population of striatal inhibitory interneurons, the TAC3 interneurons5. However, there has not yet been a detailed analysis of the spatial and phylogenetic distribution of this population. Here, we profile single cell gene expression in the developing pig (an ungulate) and ferret (a carnivore), representing 94 million years divergence from primates, and assign newborn inhibitory neurons to initial classes first specified during development6. We find that the initial class of TAC3 interneurons represents an ancestral striatal population that is also deployed towards the cortex in pig and ferret. In adult mouse, we uncover a rare population expressing Tac2, the ortholog of TAC3, in ventromedial striatum, prompting a reexamination of developing mouse striatal interneuron initial classes by targeted enrichment of their precursors. We conclude that the TAC3 interneuron initial class is conserved across Boreoeutherian mammals, with the mouse population representing Th striatal interneurons, a subset of which expresses Tac2. This study suggests that initial classes of telencephalic inhibitory neurons are largely conserved and that during evolution, neuronal types in the mammalian brain change through redistribution and fate refinement, rather than by derivation of novel precursors early in development.
Project description:Chronic stress is a major triggering factor for neuropsychiatric disorders including obsessive-compulsive disorder (OCD), a mental health condition characterized by motor stereotypies and striatal overactivation. However, the mechanisms at the cell- and microcircuit-level through which stress triggers motor symptoms is currently unknown. Here, we report that chronic stress (CS) in mice alters dorsomedial striatum (DMS) function, by affecting GABAergic interneuron populations and somatostatin-positive (SOM) interneurons in particular. Specifically, we show that CS impairs communication between SOM interneurons and medium spiny neurons, promoting striatal overactivation / disinhibition and increased motor output. Using probabilistic machine learning for analyzing animal behavior we further demonstrate that in vivo chemogenetic manipulation of SOM interneurons in DMS modulates motor phenotypes in stressed mice. Altogether, we propose a causal link between dysfunction of striatal SOM interneurons and motor symptoms in stress-related neuropsychiatric disorders.
Project description:In this study we performed single-cell sequencing of striatal interneurons, revealing striatal populations as well as the relation to their telencephalic counterparts
Project description:Interneurons are fundamental cells for maintaining the excitation-inhibition balance in the brain in health and disease. While interneurons have been shown to play a key role in the pathophysiology of autism spectrum disorder (ASD) in adult mice, little is known about how their maturation is altered in the developing striatum in ASD. Here, we aimed to track striatal developing interneurons and elucidate the molecular and physiological alterations in the Cntnap2 knockout mouse model. Using Stereo-seq and single-cell RNA sequencing data, we first characterized the pattern of expression of Cntnap2 in the adult brain and at embryonic stages in the medial ganglionic eminence (MGE), a transitory structure producing most cortical and striatal interneurons. We found that Cntnap2 is enriched in the striatum, compared to the cortex, particularly in the developing striatal cholinergic interneurons. We then revealed enhanced MGE-derived cell proliferation, followed by increased cell loss during the canonical window of developmental cell death in the Cntnap2 knockout mice. We uncovered specific cellular and molecular alterations in the developing Lhx6-expressing cholinergic interneurons of the striatum, which impacts interneuron firing properties during the first postnatal week. Overall, our work unveils some of the mechanisms underlying the shift in the developmental trajectory of striatal interneurons which greatly contribute to the ASD pathogenesis.
Project description:This experiment was designed to compare the transcriptomic differences between two parvalbumin (PV) interneuron population of the mouse brain. These two populations have the same embryological origin and share several neurochemical and electrophysiological properties, but differ in their ability to express the glial cell line-derived neurotrophic factor GDNF (negative in cortex and positive in striatum). Two different reporters for PV expressing cells were used: i) a constitutive tdTomato gene inserted in the Pvalb locus, and ii) a PV-Cre; tdTomato model in which fluorescent cells are PV cells expressing Cre recombinase. The comparative gene expression analysis between PV neurons captured from striatum and cortex allowed unraveling differential molecular characteristics of GDNF-synthesizing striatal PV interneurons and their potential role in endogenous GDNF modulation. The specific expression of several genes of interest in the striatal PV interneurons has been validated by other methods (real-time RT-PCR, in situ hibridization, immunohistochemistry).
Project description:In order to investigate age-dependent mRNA expression in mouse striatal interneurons, we performed single cell RNA-seq on FACS-isolated fluorescently labeled cells from the dorsal striatum of two mouse lines, 5ht3aEGFP or Lhx6cre::R26R-tdTomat, from either P21-26 or P55-76 animals. We included the ventricular side of the striatum that contains adult born neuroblasts destined for the olfactory bulb.