Natalia V. De Marco Garcia - US grants

Project Summary (30 lines) Experimental evidence supports the model that an imbalance in inhibitory and excitatory activity contributes to many neurological disorders including epilepsy, schizophrenia, anxiety, autism spectrum disorders and attention deficit/hyperactivity disorder. In the cerebral cortex, gamma-aminobutyric acid (GABA)ergic cortical interneurons are the major source of inhibition and are known to be critical in maintaining activity balance in the mature animal. However, the notion that developmental perturbations in GABAergic activity lead to defects in the formation of cortical circuits with lasting structural and functional deficits that provide the substrate for neurological illness, has not been explored in detail. The long-term goal of this research is to uncover how early interneuron dysfunction in the developing pre and postnatal brain leads to lasting neurological pathologies. The objective of this proposal is to reveal how extrinsic cues (nurture) and genetic programs (nature) conspire to control interneuron circuit assembly during critical windows of perinatal development. To this end, we will use the murine barrel cortex as a well-established model for the study of activity-dependent circuit maturation and one that is inherently and robustly linked to the animal's extrinsic environment. Sensory experience induces plasticity of sensory circuits in the cerebral cortex and is essential for sculpting neuronal connectivity. However, the precise role of a diversity of specific interneuron subtypes in this process is incompletely understood. We will focus our studies in cortical interneurons since our previous work indicates that these neurons are exquisitely sensitive to environmental perturbations in the neonate. In the near term, this proposal is aimed at revealing the identity interneurons subtypes that are activated by sensory cues (Aim 1). In addition, this project will assess how activity-dependent genetic programs regulate the emergence of early connectivity (Aim 2). Finally, we wish to investigate the role of cortical interneurons in the formation of sensory maps (Aim 3). With respect to outcomes, our work is expected to identify neuronal types that regulate the emergence of functional interneuron circuits. Given the accumulating experimental evidence implicating interneuron dysfunction in brain disorders, understanding the mechanisms underlying activity-dependent plasticity for these interneurons can provide invaluable insights for the development of therapeutic strategies

DESCRIPTION (provided by applicant): Abnormal proliferation and differentiation of neural progenitors in the developing cerebral cortex can cause brain malformation and result in dysregulation of brain function such as epilepsy and mental retardation. Emerging evidence has shown that similar to protein coding genes, noncoding microRNAs (miRNAs) play critical roles in cortical development and are associated with the etiology of human neurological disorders. Our previous studies have demonstrated miRNA functions in cortical development by generating Dicer conditional knockout mice, in which miRNA biogenesis is specifically blocked in the embryonic cortex. We have identified potential miRNA target genes using proteomic approaches and RNA sequencing technique. We have also examined the role of specific miRNAs in cortical development. miRNAs are often located in the intronic regions of coding genes and transcribed together with host genes. However, the knowledge gap is how intronic miRNAs interact with target genes and host genes, and how expressions of miRNAs, target genes and host genes are precisely and properly regulated during cortical development. In this project, we will test a hypothesis that a regulatory loop of miRNAs, their target genes and host genes works cohesively to ensure proper development of neural progenitors in the developing cortex. Our preliminary study has identified a family of intronic miRNAs that is expressed in the developing mouse cortex. We have developed new tools to alter miRNA expression levels and to examine the specificity of miRNA silencing effects on target genes in vitro and in vivo during cortical development. Based on these findings, our proposed research focuses on three specific aims: Aim 1 is to determine the role of this miRNA family in controlling neural progenitor proliferation and differentiation in vivo and in a culture system. Aim 2 is to elucidate molecular mechanisms of the miRNA regulation by identifying specific target genes. Aim 3 is to reveal the feedback regulation of the miRNA target gene on expression of this miRNA and its host gene in the process of controlling accurate numbers of cortical neural progenitors and proper neurogenesis. Our proposal will address a fundamental question of how a regulatory loop of miRNAs, their target genes and host genes controls proper cortical development. The success of our project should allow us to generate new tools to manipulate expressions of miRNAs and their target genes in vitro and in vivo. Because proper development of cortical neural progenitors is essential for normal brain function, our proposal should provide significant insights into developing a new diagnostic and therapeutic means using miRNAs for human brain malformations and neurological disorders.

Project Summary In the cerebral cortex, gamma-aminobutyric acid (GABA)ergic interneurons are the major source of inhibition. Interneuron dysfunction is strongly associated with autism and childhood epilepsy. We demonstrated that environmental influences such as electrical activity are fundamental for the maturation of GABAergic circuits. However, the identity of the activity patterns controlling interneuron development remains poorly understood. The long-term goal of this research is to uncover how early interneuron dysfunction leads to lasting neuropathologies. The objective of this proposal is to reveal the signaling pathways underlying activity- dependent development and to assess how perturbations in this process lead to aberrant brain function. To this end, we will use the murine barrel cortex as a well-established model for the study of activity-dependent circuit maturation. We will focus our studies in superficial circuits since our previous work indicates that these circuits are exquisitely sensitive to environmental perturbations in the neonate. In the near term, this proposal is aimed at investigating the role of specific interneuron subtypes in regulating the emergence of long range connectivity (Aim 1). In addition, this project will determine the role of GABAergic inputs for the functional maturation of pyramidal networks. We will study the role of Gabrb3, a gene encoding for the beta3 subunit of GABAA channel. Mutations in this gene are strongly associated with Angelman syndrome and ASD (Aim 2). Finally, we will assess how developmental defects in early GABAergic signaling lead to abnormal brain activity in cortico-cortical pathways during development (Aim 3). With respect to the outcomes, our work is expected to identify basic mechanisms fundamental for the emergency of a healthy E/I balance. In addition, these results are expected to have a significant translational impact because they will expand our mechanistic knowledge on how mutations in the GABRB3 gene may lead to behavioral abnormalities frequently observed in ASD patients.

Project Summary In the cerebral cortex, gamma-aminobutyric acid (GABA)ergic interneurons are the major source of inhibition. Interneuron dysfunction is strongly associated with autism and childhood epilepsy. We demonstrated that environmental influences such as electrical activity are fundamental for the maturation of GABAergic circuits. However, the identity of the activity patterns controlling interneuron development remains poorly understood. The long-term goal of this research is to uncover how early interneuron dysfunction leads to lasting neuropathologies. The objective of this proposal is to reveal the signaling pathways underlying activity- dependent development and to assess how perturbations in this process lead to aberrant brain function. To this end, we will use the murine barrel cortex as a well-established model for the study of activity-dependent circuit maturation. We will focus our studies in cortical interneurons since our previous work indicates that these neurons are exquisitely sensitive to environmental perturbations in the neonate. In the near term, this proposal is aimed at investigating the role of specific interneuron subtypes in regulating the emergence of early activity patterns (Aim 1). In addition, this project will determine the calcium-dependent signaling pathways for the functional maturation of interneuron networks. We will study the role of Cacna1c, a gene encoding for the Cav1.2 subunit of L-type calcium channels. Mutations in this gene are strongly associated with Timothy syndrome and other neurodevelopmental disorders (Aim 2). Finally, we will assess how developmental defects in interneuron number lead to abnormal brain activity during development and impaired behavior in the adult (Aim 3). With respect to the outcomes, our work is expected to identify basic mechanisms fundamental for the emergency of a healthy balance in the number of excitatory and inhibitory neurons. In addition, these results are expected to have a significant translational impact because they will expand our mechanistic knowledge on how mutations in the CACNA1C gene, strongly associated with autism, bipolar disorder, schizophrenia and Timothy syndrome, may lead to behavioral abnormalities frequently observed in these patients.