Generation of a microglial developmental index in mice and in humans reveals a sex difference in maturation and immune reactivity.

Evidence suggests many neurological disorders emerge when normal neurodevelopmental trajectories are disrupted, i.e., when circuits or cells do not reach their fully mature state. Microglia play a critical role in normal neurodevelopment and are hypothesized to contribute to brain disease. We used whole transcriptome profiling with Next Generation sequencing of purified developing microglia to identify a microglial developmental gene expression program involving thousands of genes whose expression levels change monotonically (up or down) across development. Importantly, the gene expression program was delayed in males relative to females and exposure of adult male mice to LPS, a potent immune activator, accelerated microglial development in males. Next, a microglial developmental index (MDI) generated from gene expression patterns obtained from purified mouse microglia, was applied to human brain transcriptome datasets to test the hypothesis that variability in microglial development is associated with human diseases such as Alzheimer's and autism where microglia have been suggested to play a role. MDI was significantly increased in both Alzheimer's Disease and in autism, suggesting that accelerated microglial development may contribute to neuropathology. In conclusion, we identified a microglia-specific gene expression program in mice that was used to create a microglia developmental index, which was applied to human datasets containing heterogeneous cell types to reveal differences between healthy and diseased brain samples, and between males and females. This powerful tool has wide ranging applicability to examine microglial development within the context of disease and in response to other variables such as stress and pharmacological treatments.

Total levels of hippocampal histone acetylation predict normal variability in mouse behavior.

BACKGROUND: Genetic, pharmacological, and environmental interventions that alter total levels of histone acetylation in specific brain regions can modulate behaviors and treatment responses. Efforts have been made to identify specific genes that are affected by alterations in total histone acetylation and to propose that such gene specific modulation could explain the effects of total histone acetylation levels on behavior - the implication being that under naturalistic conditions variability in histone acetylation occurs primarily around the promoters of specific genes. METHODS/RESULTS: Here we challenge this hypothesis by demonstrating with a novel flow cytometry based technique that normal variability in open field exploration, a hippocampus-related behavior, was associated with total levels of histone acetylation in the hippocampus but not in other brain regions. CONCLUSIONS: Results suggest that modulation of total levels of histone acetylation may play a role in regulating biological processes. We speculate in the discussion that endogenous regulation of total levels of histone acetylation may be a mechanism through which organisms regulate cellular plasticity. Flow cytometry provides a useful approach to measure total levels of histone acetylation at the single cell level. Relating such information to behavioral measures and treatment responses could inform drug delivery strategies to target histone deacetylase inhibitors and other chromatin modulators to places where they may be of benefit while avoiding areas where correction is not needed and could be harmful.

Studying gene expression system regulation at the program level.

Understanding how gene expression systems influence biological outcomes is an important goal for diverse areas of research. Gene expression profiling allows for the simultaneous measurement of expression levels for thousands of genes and the opportunity to use this information to increase biological understanding. Yet, the best way to relate this immense amount of information to biological outcomes is far from clear. Here, a novel approach to gene expression systems research is presented that focuses on understanding gene expression systems at the level of gene expression program regulation. It is suggested that such an approach has important advantages over current techniques and may provide novel insights into how gene expression systems are regulated to shape biological outcomes such as the development of disease or response to treatment.

Amylin receptor signaling in the ventral tegmental area is physiologically relevant for the control of food intake.

The ability of amylin, a pancreatic ß-cell-derived neuropeptide, to promote negative energy balance has been ascribed to neural activation at the area postrema. However, despite amylin binding throughout the brain, the possible role of amylin signaling at other nuclei in the control of food intake has been largely neglected. We show that mRNA for all components of the amylin receptor complex is expressed in the ventral tegmental area (VTA), a mesolimbic structure mediating food intake and reward. Direct activation of VTA amylin receptors reduces the intake of chow and palatable sucrose solution in rats. This effect is mediated by reductions in meal size and is not due to nausea/malaise or prolonged suppression of locomotor activity. VTA amylin receptor activation also reduces sucrose self-administration on a progressive ratio schedule. Finally, antagonist studies provide novel evidence that VTA amylin receptor blockade increases food intake and attenuates the intake-suppressive effects of a peripherally administered amylin analog, suggesting that amylin receptor signaling in the VTA is physiologically relevant for food intake control and potentially clinically relevant for the treatment of obesity.

Measuring the maturity of the fast-spiking interneuron transcriptional program in autism, schizophrenia, and bipolar disorder.

BACKGROUND: Emerging evidence suggests that fast-spiking (FS) interneurons are disrupted in multiple neuropsychiatric disorders including autism, schizophrenia, and bipolar disorder. FS cells, which are the primary source of synaptic inhibition, are critical for temporally organizing brain activity, regulating brain maturation, and modulating critical developmental periods in multiple cortical systems. Reduced expression of parvalbumin, a marker of mature FS cells, has been reported in individuals with schizophrenia and bipolar disorder and in mouse models of schizophrenia and autism. Although these results suggest that FS cells may be immature in neuropsychiatric disease, this possibility had not previously been formally assessed. METHODS: This study used time-course global expression data from developing FS cells to create a maturation index that tracked with the developmental age of purified cortical FS cells. The FS cell maturation index was then applied to global gene expression data from human cortex to estimate the maturity of the FS cell developmental program in the context of various disease states. Specificity of the index for FS cells was supported by a highly significant correlation of maturation index measurements with parvalbumin expression levels that withstood correction for multiple covariates. CONCLUSIONS: Results suggest the FS cell developmental gene expression program is immature in autism, schizophrenia, and bipolar disorder. More broadly, the current study indicates that cell-type specific maturation indices can be used to measure the maturity of developmental programs even in data from mixed cell types such as those found in brain homogenates.

Autism and increased paternal age related changes in global levels of gene expression regulation.

A causal role of mutations in multiple general transcription factors in neurodevelopmental disorders including autism suggested that alterations in global levels of gene expression regulation might also relate to disease risk in sporadic cases of autism. This premise can be tested by evaluating for changes in the overall distribution of gene expression levels. For instance, in mice, variability in hippocampal-dependent behaviors was associated with variability in the pattern of the overall distribution of gene expression levels, as assessed by variance in the distribution of gene expression levels in the hippocampus. We hypothesized that a similar change in variance might be found in children with autism. Gene expression microarrays covering greater than 47,000 unique RNA transcripts were done on RNA from peripheral blood lymphocytes (PBL) of children with autism (n = 82) and controls (n = 64). Variance in the distribution of gene expression levels from each microarray was compared between groups of children. Also tested was whether a risk factor for autism, increased paternal age, was associated with variance. A decrease in the variance in the distribution of gene expression levels in PBL was associated with the diagnosis of autism and a risk factor for autism, increased paternal age. Traditional approaches to microarray analysis of gene expression suggested a possible mechanism for decreased variance in gene expression. Gene expression pathways involved in transcriptional regulation were down-regulated in the blood of children with autism and children of older fathers. Thus, results from global and gene specific approaches to studying microarray data were complimentary and supported the hypothesis that alterations at the global level of gene expression regulation are related to autism and increased paternal age. Global regulation of transcription, thus, represents a possible point of convergence for multiple etiologies of autism and other neurodevelopmental disorders.

Paternal transmission of complex phenotypes in inbred mice.

BACKGROUND: Inbred mice are genetically identical but nonetheless demonstrate substantial variability in complex behaviors such as activity levels in a novel environment. This variability has been associated with levels of parental care experienced early in development. Although maternal effects have been reported in biparental and uniparental strains, there have been no investigations of paternal effects in non-biparental strains in which offspring are reared exclusively by mothers. METHODS: In the uniparental inbred Balb/cJ mouse strain, we examined the relationship of paternal open-field activity to the activity of both male and female offspring in the open-field. Potential mediators of paternal transmission of behavior were examined, including maternal care, growth parameters, litter characteristics, and time the father was present with the pregnant mother prenatally. RESULTS: An association of paternal open-field activity with the open-field activity of female but not male offspring was found. Variation in maternal postnatal care was associated with female but not male offspring activity in the open-field but did not mediate paternal effects on offspring behavior. Paternal effects on offspring growth parameters were present, but these effects also did not mediate paternal effects on behavior. CONCLUSIONS: Paternal transmission of complex traits in genetically identical mice reared only by mothers suggests a nongenetic mechanism of inheritance potentially mediated by epigenetic factors. The exclusion of multiple mediators of paternal effects on offspring suggests the possibility of germline paternal inheritance via sperm of complex phenotypes in inbred mice. Future studies are required to examine these interesting possibilities.

Is there a genomic tone? Implications for understanding development, adaptation and treatment.

This review examines the general hypothesis that cellular plasticity may be related to genomic plasticity. Using a novel approach to microarray analysis, recent studies from our laboratory showed that, in genetically identical mice, variability in the large-scale organization of gene expression was associated with individual differences in behavior. An association of the large-scale organization of gene expression in the hippocampus with behavioral variability suggests that an important aspect of gene expression regulation had gone unrecognized with traditional genomic approaches designed to look for specific differences in gene expression levels. Here we introduce the concept of a 'genomic tone' as a global genomic property related to the levels and balance between factors that generally promote and factors that generally inhibit gene expression. We suggest that genomic tone may be related to the plasticity of the gene expression system and may be an important target for developmental and therapeutic interventions.

Putting a KAP on transcription and stress.

Chromatin regulation plays an important role in brain development and the generation of phenotypic diversity. In this issue of Neuron, Jakobsson et al. find that disruption in neurons of KAP1, a key component of transcriptional repressor complexes in the brain, results in increased anxiety-like behavior and sensitivity to stress.

Variation in the large-scale organization of gene expression levels in the hippocampus relates to stable epigenetic variability in behavior.

BACKGROUND: Despite sharing the same genes, identical twins demonstrate substantial variability in behavioral traits and in their risk for disease. Epigenetic factors-DNA and chromatin modifications that affect levels of gene expression without affecting the DNA sequence-are thought to be important in establishing this variability. Epigenetically-mediated differences in the levels of gene expression that are associated with individual variability traditionally are thought to occur only in a gene-specific manner. We challenge this idea by exploring the large-scale organizational patterns of gene expression in an epigenetic model of behavioral variability. METHODOLOGY/FINDINGS: To study the effects of epigenetic influences on behavioral variability, we examine gene expression in genetically identical mice. Using a novel approach to microarray analysis, we show that variability in the large-scale organization of gene expression levels, rather than differences in the expression levels of specific genes, is associated with individual differences in behavior. Specifically, increased activity in the open field is associated with increased variance of log-transformed measures of gene expression in the hippocampus, a brain region involved in open field activity. Early life experience that increases adult activity in the open field also similarly modifies the variance of gene expression levels. The same association of the variance of gene expression levels with behavioral variability is found with levels of gene expression in the hippocampus of genetically heterogeneous outbred populations of mice, suggesting that variation in the large-scale organization of gene expression levels may also be relevant to phenotypic differences in outbred populations such as humans. We find that the increased variance in gene expression levels is attributable to an increasing separation of several large, log-normally distributed families of gene expression levels. We also show that the presence of these multiple log-normal distributions of gene expression levels is a universal characteristic of gene expression in eurkaryotes. We use data from the MicroArray Quality Control Project (MAQC) to demonstrate that our method is robust and that it reliably detects biological differences in the large-scale organization of gene expression levels. CONCLUSIONS: Our results contrast with the traditional belief that epigenetic effects on gene expression occur only at the level of specific genes and suggest instead that the large-scale organization of gene expression levels provides important insights into the relationship of gene expression with behavioral variability. Understanding the epigenetic, genetic, and environmental factors that regulate the large-scale organization of gene expression levels, and how changes in this large-scale organization influences brain development and behavior will be a major future challenge in the field of behavioral genomics.

Therapeutic potential of a tumor-specific, MHC-unrestricted T-cell receptor expressed on effector cells of the innate and the adaptive immune system through bone marrow transduction and immune reconstitution.

T-cell receptor (TCR) with unique major histocompatibility complex (MHC)-unrestricted antigen-binding properties was isolated from a human T-cell clone specific for the tumor antigen MUC1. This TCR binds its epitope on the MUC1 protein without the requirement of processing and presentation. A single-chain Valpha/Vbeta/Cbeta (scTCR) was fused to a CD3 zeta (zeta) chain to allow expression on the surface of cells of the innate (granulocytes, macrophages, natural killer [NK] cells) as well as the adaptive (T and B cells) immune system. To test the ability of the cells of the innate immune system to reject a tumor when provided with a tumor antigen-specific TCR, we reconstituted severe combined immunodeficiency (SCID) mice with bone marrow cells transduced with a retroviral vector encoding this receptor and challenged them with a MUC1-positive human tumor. These mice controlled the growth of the tumor significantly better than the control mice. We performed a similar experiment in immunocompetent mice transgenic for human MUC1. Expression of the TCR on large percentages of cells did not result in infiltration or destruction of tissues expressing MUC1. Reconstituted mice controlled the outgrowth of a MUC1-transfected but not the parental control tumor. scTCR expression appears lifelong, suggesting a successful transduction of the self-renewing stem cells.