Laser capture microdissection and microarray analysis of dividing neural progenitor cells from the adult rat hippocampus

A truncating Aspm allele leads to a complex cognitive phenotype and region-specific reductions in parvalbuminergic neurons

Neurodevelopmental disorders are heterogeneous and identifying shared genetic aetiologies and converging signalling pathways affected could improve disease diagnosis and treatment. Truncating mutations of the abnormal spindle-like microcephaly associated (ASPM) gene cause autosomal recessive primary microcephaly (MCPH) in humans. ASPM is a positive regulator of Wnt/β-Catenin signalling and controls symmetric to asymmetric cell division. This process balances neural progenitor proliferation with differentiation during embryogenesis, the malfunction of which could interfere with normal brain development. ASPM mutations may play a role also in other neurodevelopmental disorders, nevertheless, we lack the details of how or to what extent. We therefore assessed neurodevelopmental disease and circuit endophenotypes in mice with a truncating Aspm^1-7 mutation. Aspm^1-7 mice exhibited impaired short- and long-term object recognition memory and markedly enhanced place learning in the IntelliCage®. This behaviour pattern is reminiscent of a cognitive phenotype seen in mouse models and patients with a rare form of autism spectrum disorder (ASD) as well as in mouse models of altered Wnt signalling. These alterations were accompanied by ventriculomegaly, corpus callosum dysgenesis and decreased parvalbumin (PV)+ interneuron numbers in the hippocampal Cornu Ammonis (CA) region and thalamic reticular nucleus (TRN). PV+ cell number correlated to object recognition (CA and TRN) and place learning (TRN). This opens the possibility that, as well as causing MCPH, mutant ASPM potentially contributes to other neurodevelopmental disorders such as ASD through altered parvalbuminergic interneuron development affecting cognitive behaviour. These findings provide important information for understanding the genetic overlap and improved treatment of neurodevelopmental disorders associated with ASPM.

Selective gene expression analysis of the neuroepithelial body microenvironment in postnatal lungs with special interest for potential stem cell characteristics

BACKGROUND

The pulmonary neuroepithelial body (NEB) microenvironment (ME) consists of innervated cell clusters that occur sparsely distributed in the airway epithelium, an organization that has so far hampered reliable selective gene expression analysis. Although the NEB ME has been suggested to be important for airway epithelial repair after ablation, little is known about their potential stem cell characteristics in healthy postnatal lungs. Here we report on a large-scale selective gene expression analysis of the NEB ME.

METHODS

A GAD67-GFP mouse model was used that harbors GFP-fluorescent NEBs, allowing quick selection and pooling by laser microdissection (LMD) without further treatment. A panel of stem cell-related PCR arrays was used to selectively compare mRNA expression in the NEB ME to control airway epithelium (CAE). For genes that showed a higher expression in the NEB ME, a ranking was made based on the relative expression level. Single qPCR and immunohistochemistry were used to validate and quantify the PCR array data.

RESULTS

Careful optimization of all protocols appeared to be essential to finally obtain high-quality RNA from pooled LMD samples of NEB ME. About 30% of the more than 600 analyzed genes showed an at least two-fold higher expression compared to CAE. The gene that showed the highest relative expression in the NEB ME, Delta-like ligand 3 (Dll3), was investigated in more detail. Selective Dll3 gene expression in the NEB ME could be quantified via single qPCR experiments, and Dll3 protein expression could be localized specifically to NEB cell surface membranes.

CONCLUSIONS

This study emphasized the importance of good protocols and RNA quality controls because of the, often neglected, fast RNA degradation in postnatal lung samples. It was shown that sufficient amounts of high-quality RNA for reliable complex gene expression analysis can be obtained from pooled LMD-collected NEB ME samples of postnatal lungs. Dll3 expression, which has also been reported to be important in high-grade pulmonary tumor-initiating cells, was used as a proof-of-concept to confirm that the described methodology represents a promising tool for further unraveling the molecular basis of NEB ME physiology in general, and its postnatal stem cell capacities in particular.

Hyperhomocysteinemia in ApoE-/- Mice Leads to Overexpression of Enhancer of Zeste Homolog 2 via miR-92a Regulation

Hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular diseases, such as atherosclerosis. HHcy promotes atherogenesis by modifying the histone methylation patterns and miRNA regulation. In this study, we investigated the effects of homocysteine (Hcy) on the expression of enhancer of zeste homolog 2 (EZH2), and tested our hypothesis that Hcy-induced atherosclerosis is mediated by increased EZH2 expression, which is regulated by miR-92a. The levels of EZH2 and H3K27me3 were increased in the aorta of ApoE-/- mice fed a high-methionine diet for 16 weeks, whereas miR-92a expression was decreased. Over-expression of EZH2 increased H3K27me3 level and the accumulation of total cholesterol and triglycerides in the foam cells. Furthermore, upregulation of miR-92a reduced EZH2 expression in the foam cells. These data suggested that EZH2 plays a key role in Hcy-mediated lipid metabolism disorders, and that miR-92a may be a novel therapeutic target in Hcy-related atherosclerosis.

Molecular Signatures of Psychosocial Stress and Cognition Are Modulated by Chronic Lithium Treatment

Chronic psychosocial stress is an important environmental risk factor of psychiatric diseases such as schizophrenia. Social defeat in rodents has been shown to be associated with maladaptive cellular and behavioral consequences including cognitive impairments. Although gene expression changes upon psychosocial stress have been described, a comprehensive transcriptome profiling study at the global level in precisely defined hippocampal subregions which are associated with learning has been lacking. In this study, we exposed adult C57Bl/6N mice for 3 weeks to "resident-intruder" paradigm and combined laser capture microdissection with microarray analyses to identify transcriptomic signatures of chronic psychosocial stress in dentate gyrus and CA3 subregion of the dorsal hippocampus. At the individual transcript level, we detected subregion specific stress responses whereas gene set enrichment analyses (GSEA) identified several common pathways upregulated upon chronic psychosocial stress related to proteasomal function and energy supply. Behavioral profiling revealed stress-associated impairments most prominent in fear memory formation which was prevented by chronic lithium treatment. Thus, we again microdissected the CA3 region and performed global transcriptome analysis to search for molecular signatures altered by lithium treatment in stressed animals. By combining GSEA with unsupervised clustering, we detected pathways that are regulated by stress and lithium in the CA3 region of the hippocampus including proteasomal components, oxidative phosphorylation, and anti-oxidative mechanisms. Our study thus provides insight into hidden molecular phenotypes of chronic psychosocial stress and lithium treatment and proves a beneficial role for lithium treatment as an agent attenuating negative effects of psychosocial stress on cognition.

Genome-wide analysis of the oxyntic proliferative isthmus zone reveals ASPM as a possible gastric stem/progenitor cell marker over-expressed in cancer

The oxyntic proliferative isthmus zone contains the main stem/progenitor cells that provide for physiological renewal of the distinct mature cell lineages in the oxyntic epithelium of the stomach. These cells are also proposed to be the potential cells-of-origin of gastric cancer, although little is known about their molecular characteristics and specific biological markers are lacking. In this study, we developed a method for serial section-navigated laser microdissection to isolate cells from the proliferative isthmus zone of rat gastric oxyntic mucosa for genome-wide microarray gene expression analysis. Enrichment analysis showed a distinct gene expression profile for the isthmus zone, with genes regulating intracellular processes such as the cell cycle and ribosomal activity. The profile was also related to stem cell transcriptional networks and stomach neoplasia. Genes expressed uniquely in the isthmus zone were associated with E2F transcription factor 1 (E2F1), which participates in the self-renewal of stem cells and in gastric carcinogenesis. One of the unique genes was Aspm [Asp (abnormal spindle) homologue, microcephaly-associated (Drosophila)]. Here we show ASPM in single scattered epithelial cells located in the proliferative isthmus zone of rat, mouse and human oxyntic mucosa, which do not seem to be actively dividing. The ASPM-expressing cells are mainly mature cell marker-deficient, except for a limited overlap with cells with neuroendocrine and tuft cell features. Further, both ASPM and E2F1 were expressed in human gastric cancer cell lines and increased and correlated in human gastric adenocarcinomas compared to non-tumour mucosa, as shown by expression profile analyses and immunohistochemistry. The association between ASPM and the transcription factor E2F1 in gastric tissue is relevant, due to their common involvement in crucial cell fate-regulatory mechanisms. Our results thus introduce ASPM as a novel possible oxyntic stem/progenitor cell marker that may be involved in both normal gastric physiology and gastric carcinogenesis.

Conserved molecular signatures of neurogenesis in the hippocampal subgranular zone of rodents and primates

The neurogenic potential of the subgranular zone (SGZ) of the hippocampal dentate gyrus is likely to be regulated by molecular cues arising from its complex heterogeneous cellular environment. Through transcriptome analysis using laser microdissection coupled with DNA microarrays, in combination with analysis of genome-wide in situ hybridization data, we identified 363 genes selectively enriched in adult mouse SGZ. These genes reflect expression in the different constituent cell types, including progenitor and dividing cells, immature granule cells, astrocytes, oligodendrocytes and GABAergic interneurons. Similar transcriptional profiling in the rhesus monkey dentate gyrus across postnatal development identified a highly overlapping set of SGZ-enriched genes, which can be divided based on temporal profiles to reflect maturation of glia versus granule neurons. Furthermore, we identified a neurogenesis-related gene network with decreasing postnatal expression that is highly correlated with the declining number of proliferating cells in dentate gyrus over postnatal development. Many of the genes in this network showed similar postnatal downregulation in mouse, suggesting a conservation of molecular mechanisms underlying developmental and adult neurogenesis in rodents and primates. Conditional deletion of Sox4 and Sox11, encoding two neurogenesis-related transcription factors central in this network, produces a mouse with no hippocampus, confirming the crucial role for these genes in regulating hippocampal neurogenesis.

Trehalose-enhanced isolation of neuronal sub-types from adult mouse brain

Efficient isolation of specific, intact, living neurons from the adult brain is problematic due to the complex nature of the extracellular matrix consolidating the neuronal network. Here, we present significant improvements to the protocol for isolation of pure populations of neurons from mature postnatal mouse brain using fluorescence activated cell sorting (FACS). The 10-fold increase in cell yield enables cell-specific transcriptome analysis by protocols such as nanoCAGE and RNA seq.

Macrophage migration inhibitory factor mediates the antidepressant actions of voluntary exercise

Voluntary exercise is known to have an antidepressant effect. However, the underlying mechanism for this antidepressant action of exercise remains unclear, and little progress has been made in identifying genes that are directly involved. We have identified macrophage migration inhibitory factor (MIF) by analyzing existing mRNA microarray data and confirmed the augmented expression of selected genes under two experimental conditions: voluntary exercise and electroconvulsive seizure. A proinflammatory cytokine, MIF is expressed in the central nervous system and involved in innate and adaptive immune responses. A recent study reported that MIF is involved in antidepressant-induced hippocampal neurogenesis, but the mechanism remains elusive. In our data, tryptophan hydroxylase 2 (Tph2) and brain-derived neurotrophic factor (Bdnf) expression were induced after MIF treatment in vitro, as well as during both exercise and electroconvulsive seizure in vivo. This increment of Tph2 was accompanied by increases in the levels of total serotonin in vitro. Moreover, the MIF receptor CD74 and the ERK1/2 pathway mediate the MIF-induced Tph2 and Bdnf gene expression as well as serotonin content. Experiments in Mif(-/-) mice revealed depression-like behaviors and a blunted antidepressant effect of exercise, as reflected by changes in Tph2 and Bdnf expression in the forced swim test. In addition, administration of recombinant MIF protein produced antidepressant-like behavior in rats in the forced swim test. Taken together, these results suggest a role of MIF in mediating the antidepressant action of exercise, probably by enhancing serotonin neurotransmission and neurotrophic factor-induced neurogenesis in the brain.

Autosomal Recessive Primary Microcephaly (MCPH): clinical manifestations, genetic heterogeneity and mutation continuum

Autosomal Recessive Primary Microcephaly (MCPH) is a rare disorder of neurogenic mitosis characterized by reduced head circumference at birth with variable degree of mental retardation. In MCPH patients, brain size reduced to almost one-third of its original volume due to reduced number of generated cerebral cortical neurons during embryonic neurogensis. So far, seven genetic loci (MCPH1-7) for this condition have been mapped with seven corresponding genes (MCPH1, WDR62, CDK5RAP2, CEP152, ASPM, CENPJ, and STIL) identified from different world populations. Contribution of ASPM and WDR62 gene mutations in MCPH World wide is more than 50%. By and large, primary microcephaly patients are phenotypically indistinguishable, however, recent studies in patients with mutations in MCPH1, WDR62 and ASPM genes showed a broader clinical and/or cellular phenotype. It has been proposed that mutations in MCPH genes can cause the disease phenotype by disturbing: 1) orientation of mitotic spindles, 2) chromosome condensation mechanism during embryonic neurogenesis, 3) DNA damage-response signaling, 4) transcriptional regulations and microtubule dynamics, 5) certain unknown centrosomal mechanisms that control the number of neurons generated by neural precursor cells. Recent discoveries of mammalian models for MCPH have open up horizons for researchers to add more knowledge regarding the etiology and pathophysiology of MCPH. High incidence of MCPH in Pakistani population reflects the most probable involvement of consanguinity. Genetic counseling and clinical management through carrier detection/prenatal diagnosis in MCPH families can help reducing the incidence of this autosomal recessive disorder.

Primary microcephaly: do all roads lead to Rome?

The relatively large brain and expanded cerebral cortex of humans is unusual in the animal kingdom and is thought to have promoted our adaptability and success as a species. One approach for investigating neurogenesis is the study of autosomal recessive primary microcephaly (MCPH), in which prenatal brain growth is significantly reduced without an effect on brain structure. To date, eight MCPH loci and five genes have been identified. Unexpectedly, all MCPH proteins are ubiquitous and localise to centrosomes for at least part of the cell cycle. Here, we focus on recent functional studies of MCPH proteins that reveal the centrosome as a final integration point for many regulatory pathways affecting prenatal neurogenesis in mammals.

NMDA receptor subunit expression in GABAergic interneurons in the prefrontal cortex: application of laser microdissection technique

The selective involvement of a subset of neurons in many psychiatric disorders, such as gamma-aminobutyric acid (GABA)-ergic interneurons in schizophrenia, creates a significant need for in-depth analysis of these cells. Here we introduce a combination of techniques to examine the relative gene expression of N-methyl-d-aspartic acid (NMDA) receptor subtypes in GABAergic interneurons from the rat prefrontal cortex. Neurons were identified by immunostaining, isolated by laser microdissection and RNA was prepared for reverse transcription polymerase chain reaction (RT-PCR) and real-time PCR. These experimental procedures have been described individually; however, we found that this combination of techniques is powerful for the analysis of gene expression in individual identified neurons. This approach provides the means to analyze relevant molecular mechanisms that are involved in the neuropathological process of a devastating brain disorder.

Terminal and progenitor lineage-survival oncogenes as cancer markers

Tumour classification has traditionally focused on differentiation and cellular morphology, and latterly on the application of genomic approaches. By combining chromatin immunoprecipitation with expression array, it has been possible to identify direct gene targets for transcription factors for nuclear hormone receptors. At the same time, there have been great strides in deriving stem and progenitor cells from tissues. It is therefore timely to propose that pairing the isolation of these cell subpopulations from tissues and tumours with these genomics approaches will reveal conserved gene targets for transcription factors. By focusing on transcription factors (lineage-survival oncogenes) with roles in both organogenesis and tumourigenesis at multiple organ sites, we suggest that this comparative genomics approach will enable developmental biology to be used more fully in relation to understanding tumour progression and will reveal new cancer markers. We focus here on neurogenesis and neuroendocrine differentiation in tumours.

Differentiation of neural stem cells into oligodendrocytes: involvement of the polycomb group protein Ezh2

The mechanisms underlying the regulation of neural stem cell (NSC) renewal and maintenance of their multipotency are still not completely understood. Self-renewal of stem cells in general implies repression of genes that encode for cell lineage differentiation. Enhancer of zeste homolog 2 (Ezh2) is a Polycomb group protein involved in stem cell renewal and maintenance by inducing gene silencing via histone methylation and deacetylation. To establish the role of Ezh2 in the maintenance and differentiation of NSCs, we have examined the expression of Ezh2 in NSCs isolated from embryonic (embryonic day 14) mice during proliferation and differentiation in vitro. Our results show that Ezh2 is highly expressed in proliferating NSCs. In accordance with its suggested role as a transcription repressor, the expression of Ezh2 decreased when the NSCs differentiated into neurons and was completely suppressed during differentiation into astrocytes. Surprisingly, Ezh2 remained highly expressed in NSCs that differentiated into an oligodendrocytic cell lineage, starting from oligodendrocyte precursor cells (OPCs) up to the immature (premyelinating) oligodendrocyte stage. To further establish the role of Ezh2 in NSC differentiation, we silenced and induced overexpression of the Ezh2 gene in NSCs. High levels of Ezh2 in differentiating NSCs appeared to be associated with an increase in oligodendrocytes and a reduction in astrocytes, whereas low levels of Ezh2 led to completely opposite effects. The increase in the number of oligodendrocytes induced by enhanced expression of Ezh2 could be ascribed to stimulation of OPC proliferation although stimulation of oligodendrocyte differentiation cannot be excluded. Disclosure of potential conflicts of interest is found at the end of this article.

Genes, plasticity and mental retardation

Functional and structural plasticity is a fundamental property of the brain involved in diverse processes ranging from brain construction and repair to storage of experiences during lifetime. Our current understanding of different forms of brain plasticity mechanisms has advanced tremendously in the last decades, benefiting from studies of development and memory storage in adulthood and from investigations of diverse diseased conditions. In this review, we focus on the role of mental retardation (MR) genes and show how this developing area of research can enrich our knowledge of the cellular and molecular mechanisms of brain plasticity and cognitive functions, and of the dysfunctional mechanisms underlying MR. We describe two main groups of MR genes; those leading to dysfunctional neurodevelopmental programs and brain malformations, and those which rely on alterations in molecular mechanisms underlying synaptic organization and plasticity. We first explore the role of MR genes in key mechanisms of neurogenesis and neuronal migration during development and in the adult, such as actin and microtubule-cytoskeletal dynamics and signal transduction. We then define the contribution of MR genes to forms of activity-dependent synaptic modifications, such as those involved in molecular organization of the synapse, intracellular signaling regulating gene programs and neuronal cytoskeleton to control network remodeling. We trace the characteristics of MR genes playing key roles in many forms of brain plasticity mechanisms, and highlight specific MR genes that endorse distinct roles in different cell types or brain regions, and at various times of a brain lifetime.