Identification Of Novel Molecular-Genetic Pathways Regulating The Development Of Subpallial Derivatives

The embryonic subpallium produces many different neuronal cell types present throughout the adult telencephalon, including striatal medium spiny neurons (MSN) and cortical interneurons. Dysfunction of either cell type leads to neurological and psychiatric disorders including schizophrenia, epilepsy, and Tourette’s syndrome. Thus, understanding the molecular pathways that regulate their development and function has important implications for understanding disease pathogenesis. This work describes novel methods and genetic factors that expand our ability to characterize the development and function of two major subpallial derivatives: cortical interneurons and striatal MSN. The first part of this thesis characterizes a novel enrichment method for producing parvalbumin-expressing (PV) interneurons from mouse embryonic stem cells. This method, which uses an atypical protein kinase C inhibitor to enhance intermediate neurogenesis, results in a markedly increased ratio of PV+ to somatostatin-expressing interneurons. The findings suggest that the mode of neurogenesis influences cortical interneuron fate determination. Moreover, PV+ interneurons can now be generated in large numbers to study their development, screen for factors that affect their physiology, and used in therapeutic applications. The second part of this thesis examines the function of two putative transcription factors, Zswim5 and Zswim6, in the regulation of striatal development. We show that these genes are expressed in subpallial precursors, and in the case of Zswim6, expressed in the adult striatum. Next, through the generation of Zswim5 and Zswim6 knockout mice, we provide a detailed anatomical, molecular, and behavioral characterization of the resulting phenotypes. Our findings reveal that loss of Zswim6 causes a reduction in striatal volume and morphological changes in MSN. Additionally, these structural changes are associated with alterations in motor behaviors including hyperactivity, impaired rotarod performance, and hyperresponsiveness to amphetamine. These results demonstrate that Zswim6 is indispensable for normal brain development and support findings in human genome-wide association studies that implicate Zswim6 with schizophrenia. Collectively, this dissertation provides novel insights into telencephalic development through the development of in vitro stem cell systems and in vivo disease mouse models that further our ability to test and understand neurological diseases

Polygenic and environmental determinants of tics in the Avon Longitudinal Study of Parents and Children

Tourette syndrome (TS) is caused by multiple genetic and environmental factors. Yet, little is known about the interplay of these factors in the occurrence of tics. We investigated whether polygenic risk score (PRS) of TS and pregnancy-related factors together enhance the explained variance of tic occurrence in the Avon Longitudinal Study of Parents and Children (Ncases = 612; Ncontrols = 4,201; 50% male; mean age 13.8 years). We included a cumulative adverse pregnancy risk score, maternal anxiety and depression, and maternal smoking and alcohol use during pregnancy. We investigated possible joint effects of genetic and pregnancy-related risk factors using a multivariable approach, and explored mediation effects between the pregnancy-related risk factors in explaining tic presence. The PRS and the cumulative adverse pregnancy risk score, maternal anxiety, or maternal depression explained significantly more variance of tic presence compared to models including only the PRS. Furthermore, we found that the cumulative adverse pregnancy risk score mediated the association between several pregnancy-related factors (maternal anxiety, depression, and smoking) and tics. The combination of a PRS and pregnancy-related risk factors explained more variance of tics in a general population cohort compared to studying these factors in isolation.</p

RORβ Induces Barrel-like Neuronal Clusters in the Developing Neocortex

Neurons in layer IV of the rodent whisker somatosensory cortex are tangentially organized in periodic clusters called barrels, each of which is innervated by thalamocortical axons transmitting sensory information from a single principal whisker, together forming a somatotopic map of the whisker pad. Proper thalamocortical innervation is critical for barrel formation during development, but the molecular mechanisms controlling layer IV neuron clustering are unknown. Here, we investigate the role in this mapping of the nuclear orphan receptor RORβ, which is expressed in neurons in layer IV during corticogenesis. We find that RORβ protein expression specifically increases in the whisker barrel cortex during barrel formation and that in vivo overexpression of RORβ is sufficient to induce periodic barrel-like clustering of cortical neurons. Remarkably, this clustering can be induced as early as E18, prior to innervation by thalamocortical afferents and whisker derived-input. At later developmental stages, these ectopic neuronal clusters are specifically innervated by thalamocortical axons, demonstrated by anterograde labeling from the thalamus and by expression of thalamocortical-specific synaptic markers. Together, these data indicate that RORβ expression levels control cytoarchitectural patterning of neocortical neurons during development, a critical process for the topographical mapping of whisker input onto the cortical surfac

Ethanol Activates Immune Response In Lymphoblastoid Cells

The short term effects of alcohol on gene expression in brain tissue cannot directly be studied in humans. Because neuroimmune signaling is altered by alcohol, immune cells are a logical, accessible choice to study and might provide biomarkers. RNAseq was used to study the effects of 48 h exposure to ethanol on lymphoblastoid cell lines (LCLs) from 21 alcoholics and 21 controls. Ethanol exposure resulted in differential expression of 4,577 of the 12,526 genes detectably expressed in the LCLs (FDR ≤ 0.05); 55% of these showed increased expression. Cells from alcoholics and controls responded similarly. The genes whose expression changed fell into many pathways. NFκB, neuroinflammation, IL-6, and dendritic cell maturation pathways were activated, consistent with increased signaling by NFκB, TNF, TGFβ, IL1, IL4, IL18, TLR4, and LPS. Signaling by Interferons A and B decreased, which may be responsible for a slightly blunted immune response compared to 24 h ethanol treatment. EIF2, phospholipase C and VEGF signaling were decreased. Baseline gene expression patterns were similar in LCLs from alcoholics and controls. At relaxed stringency (p<0.05), 1164 genes differed, 340 of which were also affected by ethanol. There was a suggestion of compensation, with 77% showing opposing fold changes. Aldosterone signaling and phospholipase C signaling differed. The pattern of expression was consistent with increased signaling by several cytokines and TLR2 in alcoholics. The cholesterol biosynthesis pathway was lower in alcoholics, including a decrease in the rate-limiting enzyme HMGCR. LCLs show many effects of ethanol exposure, some of which might provide biomarkers for AUD and aid in interpreting the effects of genes identified by GWAS

Positive selection on loci associated with drug and alcohol dependence

Much of the evolution of human behavior remains a mystery, including how certain disadvantageous behaviors are so prevalent. Nicotine addiction is one such phenotype. Several loci have been implicated in nicotine related phenotypes including the nicotinic receptor gene clusters (CHRNs) on chromosomes 8 and 15. Here we use 1000 Genomes sequence data from 3 populations (Africans, Asians and Europeans) to examine whether natural selection has occurred at these loci. We used Tajima's D and the integrated haplotype score (iHS) to test for evidence of natural selection. Our results provide evidence for strong selection in the nicotinic receptor gene cluster on chromosome 8, previously found to be significantly associated with both nicotine and cocaine dependence, as well as evidence selection acting on the region containing the CHRNA5 nicotinic receptor gene on chromosome 15, that is genome wide significant for risk for nicotine dependence. To examine the possibility that this selection is related to memory and learning, we utilized genetic data from the Collaborative Studies on the Genetics of Alcoholism (COGA) to test variants within these regions with three tests of memory and learning, the Wechsler Adult Intelligence Scale (WAIS) Block Design, WAIS Digit Symbol and WAIS Information tests. Of the 17 SNPs genotyped in COGA in this region, we find one significantly associated with WAIS digit symbol test results. This test captures aspects of reaction time and memory, suggesting that a phenotype relating to memory and learning may have been the driving force behind selection at these loci. This study could begin to explain why these seemingly deleterious SNPs are present at their current frequencies

Defining alcohol-related phenotypes in humans. The Collaborative Study on the Genetics of Alcoholism.

Alcoholism is a disease that runs in families and results at least in part from genetic risk factors. The Collaborative Study on the Genetics of Alcoholism (COGA) is a Federally funded effort to identify and characterize those genetic factors. The study involves more than 1,000 alcoholic subjects and their families, with researchers conducting comprehensive psychological, physiological, electrophysiological, and genetic analyses of the participants. These analyses have identified several traits, or phenotypes, that appear to be genetically determined, such as the presence of alcohol dependence, the level of response to alcohol, the presence of coexisting depression, or the maximum number of drinks a person consumes per occasion. Genetic analyses have identified regions on several chromosomes that are associated with these phenotypes and need to be studied further