Expression of LIM protein genes Lmo1, Lmo2, and Lmo3 in adult mouse hippocampus and other forebrain regions: differential regulation by seizure activity

Transcription factor expression defines subclasses of developing projection neurons highly similar to single-cell RNA-seq subtypes

We are only just beginning to catalog the vast diversity of cell types in the cerebral cortex. Such categorization is a first step toward understanding how diversification relates to function. All cortical projection neurons arise from a uniform pool of progenitor cells that lines the ventricles of the forebrain. It is still unclear how these progenitor cells generate the more than 50 unique types of mature cortical projection neurons defined by their distinct gene-expression profiles. Moreover, exactly how and when neurons diversify their function during development is unknown. Here we relate gene expression and chromatin accessibility of two subclasses of projection neurons with divergent morphological and functional features as they develop in the mouse brain between embryonic day 13 and postnatal day 5 in order to identify transcriptional networks that diversify neuron cell fate. We compare these gene-expression profiles with published profiles of single cells isolated from similar populations and establish that layer-defined cell classes encompass cell subtypes and developmental trajectories identified using single-cell sequencing. Given the depth of our sequencing, we identify groups of transcription factors with particularly dense subclass-specific regulation and subclass-enriched transcription factor binding motifs. We also describe transcription factor-adjacent long noncoding RNAs that define each subclass and validate the function of Myt1l in balancing the ratio of the two subclasses in vitro. Our multidimensional approach supports an evolving model of progressive restriction of cell fate competence through inherited transcriptional identities.

Mapping developmental trajectories and subtype diversity of normal and glaucomatous human retinal ganglion cells by single-cell transcriptome analysis

Glaucoma is characterized by a progressive degeneration of retinal ganglion cells (RGCs), leading to irreversible vision loss. Currently, there is no effective treatment for RGC degeneration. We used a disease-in-a-dish stem cell model to examine the developmental susceptibility of RGCs to glaucomatous degeneration, which may inform on the formulation of therapeutic approaches. Here, we used single-cell transcriptome analysis of SIX6 risk allele (SIX6^{risk allele} ) primary open angle glaucoma patient-specific and control hRGCs to compare developmental trajectories in terms of lineage- and stage-specific transcriptional signature to identify dysregulated stages/genes, and subtype composition to estimate the relative vulnerability of RGCs to degeneration because their ability to regenerate axons are subtype-specific. The developmental trajectories, beginning from neural stem cells to RGCs, were similar between SIX6^{risk allele} and control RGCs. However, the differentiation of SIX6^{risk allele} RGCs was relatively stalled at the retinal progenitor cell stage, compromising the acquisition of mature phenotype and subtype composition, compared with controls, which was likely due to dysregulated mTOR and Notch signaling pathways. Furthermore, SIX6^{risk allele} RGCs, as compared with controls, expressed fewer genes corresponding to RGC subtypes that are preferentially resistant to degeneration. The immature phenotype of SIX6^{risk allele} RGCs with underrepresented degeneration-resistant subtypes may make them vulnerable to glaucomatous degeneration.

Lmo3 deficiency in the mouse is associated with alterations in mood-related behaviors and a depression-biased amygdala transcriptome

The highly conserved transcription factor LIM-only 3 (Lmo3) is involved in important neurodevelopmental processes in several brain areas including the amygdala, a central hub for the generation and regulation of emotions. Accordingly, a role for Lmo3 in the behavioral responses to ethanol and in the display of anxiety-like behavior in mice has been demonstrated while the potential involvement of Lmo3 in the control of mood-related behavior has not yet been explored. Using a mouse model of Lmo3 depletion (Lmo3z), we here report that genetic Lmo3 deficiency is associated with altered performance in behavioral paradigms assessing anxiety-like and depression-like traits and additionally accompanied by impairments in learned fear. Importantly, long-term potentiation (LTP) in the basolateral amygdala (BLA), a proposed cellular correlate of fear learning, is impaired in Lmo3z mice. RNA-Seq analysis of BLA tissue and gene set enrichment analysis (GSEA) of differentially expressed genes in Lmo3z mice reveals a significant overlap between genes overexpressed in Lmo3z mice and those enriched in the amygdala of a cohort of patients suffering from major depressive disorder. Consequently, we propose that Lmo3 may play a role in the regulation of gene networks that are relevant to the regulation of emotions. Future work may aid to further explore the role of Lmo3 in the pathophysiology of affective disorders and its genetic foundations.

Regulation of anxiety-like behavior and Crhr1 expression in the basolateral amygdala by LMO3

The LIM domain only protein LMO3 is a transcriptional regulator that has been shown to regulate several behavioral responses to alcohol. Specifically, Lmo3 null (Lmo3^Z) mice consume more ethanol in a binge-drinking test and show enhanced ethanol-induced sedation. Due to the high comorbidity of alcohol use and anxiety, we investigated anxiety-like behavior in Lmo3^Z mice. Lmo3^Z mice spent more time in the open arms of the elevated plus maze compared with their wild-type littermates, but the effect was confounded by reduced locomotor activity. To verify the anxiety phenotype in the Lmo3^Z mice, we tested them for novelty-induced hypophagia and found that they also showed reduced anxiety in this test. We next explored the mechanism by which LMO3 might regulate anxiety by measuring mRNA and protein levels of corticotropin releasing factor (encoded by the Crh gene) and its receptor type 1 (Crhr1) in Lmo3^Z mice. Reduced Crhr1 mRNA and protein was evident in the basolateral amygdala (BLA) of Lmo3^Z mice. To examine whether Lmo3 in the amygdala is important for anxiety-like behavior, we locally reduced Lmo3 expression in the BLA of wild type mice using a lentiviral vector expressing a short hairpin RNA targeting the Lmo3 transcript. Mice with Lmo3 knockdown in the BLA exhibited decreased anxiety-like behavior relative to control mice. These results suggest that Lmo3 promotes anxiety-like behavior specifically in the BLA, possibly by altering Crhr1 expression. This study is the first to support a role for Lmo3 in anxiety-like behavior.

Newt cells secrete extracellular vesicles with therapeutic bioactivity in mammalian cardiomyocytes

Newts can regenerate amputated limbs and cardiac tissue, unlike mammals which lack broad regenerative capacity. Several signaling pathways involved in cell proliferation, differentiation and survival during newt tissue regeneration have been elucidated, however the factors that coordinate signaling between cells, as well as the conservation of these factors in other animals, are not well defined. Here we report that media conditioned by newt limb explant cells (A1 cells) protect mammalian cardiomyocytes from oxidative stress-induced apoptosis. The cytoprotective effect of A1-conditioned media was negated by exposing A1 cells to GW4869, which suppresses the generation of extracellular vesicles (EVs). A1-EVs are similar in diameter (~100–150 nm), structure, and share several membrane surface and cargo proteins with mammalian exosomes. However, isolated A1-EVs contain significantly higher levels of both RNA and protein per particle than mammalian EVs. Additionally, numerous cargo RNAs and proteins are unique to A1-EVs. Of particular note, A1-EVs contain numerous mRNAs encoding nuclear receptors, membrane ligands, as well as transcription factors. Mammalian cardiomyocytes treated with A1-EVs showed increased expression of genes in the PI3K/AKT pathway, a pivotal player in survival signaling. We conclude that newt cells secrete EVs with diverse, distinctive RNA and protein contents. Despite ~300 million years of evolutionary divergence between newts and mammals, newt EVs confer cytoprotective effects on mammalian cardiomyocytes.

Molecular Diversity of Midbrain Development in Mouse, Human, and Stem Cells

Understanding human embryonic ventral midbrain is of major interest for Parkinson's disease. However, the cell types, their gene expression dynamics, and their relationship to commonly used rodent models remain to be defined. We performed single-cell RNA sequencing to examine ventral midbrain development in human and mouse. We found 25 molecularly defined human cell types, including five subtypes of radial glia-like cells and four progenitors. In the mouse, two mature fetal dopaminergic neuron subtypes diversified into five adult classes during postnatal development. Cell types and gene expression were generally conserved across species, but with clear differences in cell proliferation, developmental timing, and dopaminergic neuron development. Additionally, we developed a method to quantitatively assess the fidelity of dopaminergic neurons derived from human pluripotent stem cells, at a single-cell level. Thus, our study provides insight into the molecular programs controlling human midbrain development and provides a foundation for the development of cell replacement therapies.

LMO2 at 25 years: a paradigm of chromosomal translocation proteins

LMO2 was first discovered through proximity to frequently occurring chromosomal translocations in T cell acute lymphoblastic leukaemia (T-ALL). Subsequent studies on its role in tumours and in normal settings have highlighted LMO2 as an archetypical chromosomal translocation oncogene, activated by association with antigen receptor gene loci and a paradigm for translocation gene activation in T-ALL. The normal function of LMO2 in haematopoietic cell fate and angiogenesis suggests it is a master gene regulator exerting a dysfunctional control on differentiation following chromosomal translocations. Its importance in T cell neoplasia has been further emphasized by the recurrent findings of interstitial deletions of chromosome 11 near LMO2 and of LMO2 as a target of retroviral insertion gene activation during gene therapy trials for X chromosome-linked severe combined immuno-deficiency syndrome, both types of event leading to similar T cell leukaemia. The discovery of LMO2 in some B cell neoplasias and in some epithelial cancers suggests a more ubiquitous function as an oncogenic protein, and that the current development of novel inhibitors will be of great value in future cancer treatment. Further, the role of LMO2 in angiogenesis and in haematopoietic stem cells (HSCs) bodes well for targeting LMO2 in angiogenic disorders and in generating autologous induced HSCs for application in various clinical indications.

MiR-101 reverses the hypomethylation of the LMO3 promoter in glioma cells

LIM-only protein 3 (LMO3), a member of the LIM-only protein group, is a new DNA methylation gene that was identified in gliomas via the MeDIP-Chip in our previous study. In this study, we found that LIM-only protein 3 (LMO3) is hypomethylated and overexpressed in glioma cells and tissues. The overexpression of LMO3 was correlated with a poor prognosis in glioma patients, and LMO3 was indirectly inhibited by the tumor suppressor miR-101, which is a potential prognosis marker of gliomas. MiR-101 decreased the expression of LMO3 by reversing the methylation status of the LMO3 promoter and by inhibiting the presence of the methylation-related histones H3K4me2 and H3K27me3 and increasing the presence of H3K9me3 and H4K20me3 on the promoter. It was determined that miR-101 decreases the occupancy of H3K27me3 by inhibiting EZH2, DNMT3A and EED and decreases the H3K9me3 occupancy on the LMO3 promoter via SUV39H1, SUV39H2, G9a and PHF8. Furthermore, miR-101 suppresses the expression of LMO3 by decreasing USF and MZF1.

Increased behavioral responses to ethanol in Lmo3 knockout mice

LIM-domain-only 3 (LMO3) is a transcriptional regulator involved in central nervous system development and neuroblastoma. Our previous studies implicated a potential role for LMO3 in regulating ethanol sensitivity and consumption. Here, we examined behavioral responses to ethanol in a line of Lmo3 null (Lmo3(Z) ) mice, utilizing the ethanol-induced loss-of-righting-reflex (LORR) test, two-bottle choice ethanol consumption and the drinking in the dark (DID) test, which models binge-like ethanol consumption. We found that Lmo3(Z) mice exhibited increased sedation time in response to ethanol in the LORR test and drank significantly more ethanol in the DID test compared with their wild-type counterparts, but showed no differences in two-bottle choice ethanol consumption. To explore where LMO3 may be acting in the brain to produce an ethanol phenotype, we also examined reporter gene (β-galactosidase) expression in heterozygous Lmo3(Z) mice and found strong expression in subcortical areas, particularly in those areas implicated in drug abuse, including the nucleus accumbens (Acb), cortex, hippocampus and amygdala. We also examined Lmo3 expression in the brains of wild-type mice who had undergone the DID test and found a negative correlation between Lmo3 expression in the Acb and the amount of ethanol consumed, consistent with the increased binge-like drinking observed in Lmo3(Z) mice. These results support a role for LMO3 in regulating behavioral responses to ethanol, potentially through its actions in the Acb.

Transcriptional analysis of apoptotic cerebellar granule neurons following rescue by gastric inhibitory polypeptide

Apoptosis triggered by exogenous or endogenous stimuli is a crucial phenomenon to determine the fate of neurons, both in physiological and in pathological conditions. Our previous study established that gastric inhibitory polypeptide (Gip) is a neurotrophic factor capable of preventing apoptosis of cerebellar granule neurons (CGNs), during its pre-commitment phase. In the present study, we conducted whole-genome expression profiling to obtain a comprehensive view of the transcriptional program underlying the rescue effect of Gip in CGNs. By using DNA microarray technology, we identified 65 genes, we named survival related genes, whose expression is significantly de-regulated following Gip treatment. The expression levels of six transcripts were confirmed by real-time quantitative polymerase chain reaction. The proteins encoded by the survival related genes are functionally grouped in the following categories: signal transduction, transcription, cell cycle, chromatin remodeling, cell death, antioxidant activity, ubiquitination, metabolism and cytoskeletal organization. Our data outline that Gip supports CGNs rescue via a molecular framework, orchestrated by a wide spectrum of gene actors, which propagate survival signals and support neuronal viability.

Seizure evoked regulation of LIM-HD genes and co-factors in the postnatal and adult hippocampus

The LIM-homeodomain (LIM-HD) family of transcription factors is well known for its functions during several developmental processes including cell fate specification, cell migration and axon guidance, and its members play fundamental roles in hippocampal development. The hippocampus is a structure that displays striking activity dependent plasticity.  We examined whether LIM-HD genes and their co-factors are regulated during kainic acid induced seizure in the adult rat hippocampus as well as in early postnatal rats, when the hippocampal circuitry is not fully developed.  We report a distinct and field-specific regulation of LIM-HD genes Lhx1,Lhx2, and Lhx9, LIM-only gene Lmo4, and cofactor Clim1a in the adult hippocampus after seizure induction. In contrast none of these genes displayed altered levels upon induction of seizure in postnatal animals.  Our results provide evidence of temporal and spatial seizure mediated regulation of LIM-HD family members and suggest that LIM-HD gene function may be involved in activity dependent plasticity in the adult hippocampus

LIM-domain-only proteins in cancer

LIM-domain proteins are a large family of proteins that are emerging as key molecules in a wide variety of human cancers. In particular, all members of the human LIM-domain-only (LMO) proteins, LMO1-4, which are required for many developmental processes, are implicated in the onset or the progression of several cancers, including T cell leukaemia, breast cancer and neuroblastoma. These small proteins contain two protein-interacting LIM domains but little additional sequence, and they seem to function by nucleating the formation of new transcriptional complexes and/or by disrupting existing transcriptional complexes to modulate gene expression programmes. Through these activities, the LMO proteins have important cellular roles in processes that are relevant to cancer such as self-renewal, cell cycle regulation and metastasis. These functions highlight the therapeutic potential of targeting these proteins in cancer.

LMO4 inhibits p53-mediated proliferative inhibition of breast cancer cells through interacting p53

AIMS

The LIM domain only proteins (LMOs) which consist of four members (LMO1-LMO4) are a family of nuclear transcription coregulators that are characterized by the exclusive presence of two tandem LIM domains and no other functional domains. They regulate gene transcription by functioning as "linker" or "scaffolding" proteins by virtue of their LIM domains and are involved in the formation of multiprotein complexes with several DNA-binding factors and transcriptional regulatory proteins. In the present study, we tried to find the physical interaction between p53 and LMO4, and the effect of LMO4 on p53-mediated proliferative inhibition of breast cancer cells.

MAIN METHODS

FCM analysis was developed to detect the apoptosis of breast cancer cells after adriamycin (ADR) treatment. RT-PCR and Western blot analysis were performed to detect the expression of LMO4 and p53-related genes and proteins. Immunoprecipitation assay was used to detect the interaction between LMO4 and p53. Colony formation assay was developed to detect the proliferation of breast cancer cells.

KEY FINDINGS

We found that p53 was induced, but LMO4 was down-regulated in response to ADR. We also found that enforced expression of p53 inhibited the expression of LMO4, suggesting that LMO4 is a direct transcriptional target of p53. Furthermore, LMO4 can interact with p53 and inhibit p53-mediated inhibition of colony formation of breast cancer MDA-MB-453 cells.

SIGNIFICANCE

The present study showed that LMO4 is a direct target of p53 and inhibits p53-mediated proliferative inhibition of breast cancer cells through interacting p53.

Lmo genes regulate behavioral responses to ethanol in Drosophila melanogaster and the mouse

BACKGROUND

Previous work from our laboratory demonstrated a role for the Drosophila Lim-only (dLmo) gene in regulating behavioral responses to cocaine. Herein, we examined whether dLmo influences the flies' sensitivity to ethanol's sedating effects. We also investigated whether 1 of the mammalian homologs of dLmo, Lmo3, is involved in behavioral responses to ethanol in mice.

METHODS

To examine dLmo function in ethanol-induced sedation, mutant flies with reduced or increased dLmo expression were tested using the loss of righting (LOR) assay. To determine whether mouse Lmo3 regulates behavioral responses to ethanol, we generated transgenic mice expressing a short-hairpin RNA targeting Lmo3 for RNA interference-mediated knockdown by lentiviral infection of single cell embryos. Adult founder mice, expressing varying amounts of Lmo3 in the brain, were tested using ethanol loss-of-righting-reflex (LORR) and 2-bottle choice ethanol consumption assays.

RESULTS

We found that in flies, reduced dLmo activity increased sensitivity to ethanol-induced sedation, whereas increased expression of dLmo led to increased resistance to ethanol-induced sedation. In mice, reduced levels of Lmo3 were correlated with increased sedation time in the LORR test and decreased ethanol consumption in the 2-bottle choice protocol.

CONCLUSIONS

These data describe a novel and conserved role for Lmo genes in flies and mice in behavioral responses to ethanol. These studies also demonstrate the feasibility of rapidly translating findings from invertebrate systems to mammalian models of alcohol abuse by combining RNA interference in transgenic mice and behavioral testing.

Identification of thyroid hormone receptor binding sites and target genes using ChIP-on-chip in developing mouse cerebellum

Thyroid hormone (TH) is critical to normal brain development, but the mechanisms operating in this process are poorly understood. We used chromatin immunoprecipitation to enrich regions of DNA bound to thyroid receptor beta (TRβ) of mouse cerebellum sampled on post natal day 15. Enriched target was hybridized to promoter microarrays (ChIP-on-chip) spanning −8 kb to +2 kb of the transcription start site (TSS) of 5000 genes. We identified 91 genes with TR binding sites. Roughly half of the sites were located in introns, while 30% were located within 1 kb upstream (5′) of the TSS. Of these genes, 83 with known function included genes involved in apoptosis, neurodevelopment, metabolism and signal transduction. Two genes, MBP and CD44, are known to contain TREs, providing validation of the system. This is the first report of TR binding for 81 of these genes. ChIP-on-chip results were confirmed for 10 of the 13 binding fragments using ChIP-PCR. The expression of 4 novel TH target genes was found to be correlated with TH levels in hyper/hypothyroid animals providing further support for TR binding. A TRβ binding site upstream of the coding region of myelin associated glycoprotein was demonstrated to be TH-responsive using a luciferase expression system. Motif searches did not identify any classic binding elements, indicating that not all TR binding sites conform to variations of the classic form. These findings provide mechanistic insight into impaired neurodevelopment resulting from TH deficiency and a rich bioinformatics resource for developing a better understanding of TR binding.

The transcription factor LMO2 is a robust marker of vascular endothelium and vascular neoplasms and selected other entities

The transcription factor LMO2 is involved in vascular and hematopoietic development and hematolymphoid neoplasia. We have demonstrated that LMO2 is expressed nearly ubiquitously in native and neoplastic vasculature, including lymphatics. LMO2 reactivity is otherwise virtually absent in nonhematolymphoid tissues except in breast myoepithelium, prostatic basal cells, and secretory phase endometrial glands. Vasculature is LMO2- in adult and fetal heart, brain of older adults, hepatic sinusoids, and hepatocellular carcinoma. LMO2 is uniformly expressed in benign vascular and lymphatic neoplasms and in most malignant vascular neoplasms with the exception of epithelioid vascular neoplasms of pleura and bone. Among nonvascular neoplasms, LMO2 reactivity is present in giant cell tumor of tendon sheath, juvenile xanthogranuloma, a subset of gastrointestinal stromal tumors, small round blue cell tumors, and myoepithelial-derived neoplasms. The restricted expression pattern, nuclear localization, and crisp staining of LMO2 in paraffin blocks make it an attractive candidate for the diagnostic immunohistochemistry laboratory.

Drosophila, a genetic model system to study cocaine-related behaviors: a review with focus on LIM-only proteins

In the last decade, the fruit fly Drosophila melanogaster, highly accessible to genetic, behavioral and molecular analyses, has been introduced as a novel model organism to help decipher the complex genetic, neurochemical, and neuroanatomical underpinnings of behaviors induced by drugs of abuse. Here we review these data, focusing specifically on cocaine-related behaviors. Several of cocaine's most characteristic properties have been recapitulated in Drosophila. First, cocaine induces motor behaviors in flies that are remarkably similar to those observed in mammals. Second, repeated cocaine administration induces behavioral sensitization a form of behavioral plasticity believed to underlie certain aspects of addiction. Third, a key role for dopaminergic systems in mediating cocaine's effects has been demonstrated through both pharmacological and genetic methods. Finally, and most importantly, unbiased genetic screens, feasible because of the simplicity and scale with which flies can be manipulated in the laboratory, have identified several novel genes and pathways whose role in cocaine behaviors had not been anticipated. Many of these genes and pathways have been validated in mammalian models of drug addiction. We focus in this review on the role of LIM-only proteins in cocaine-induced behaviors.

Identification of Lmo1 as part of a Hox-dependent regulatory network for hindbrain patterning

The embryonic functions of Hox proteins have been extensively investigated in several animal phyla. These transcription factors act as selectors of developmental programmes, to govern the morphogenesis of multiple structures and organs. However, despite the variety of morphogenetic processes Hox proteins are involved in, only a limited set of their target genes has been identified so far. To find additional targets, we used a strategy based upon the simultaneous overexpression of Hoxa2 and its cofactors Pbx1 and Prep in a cellular model. Among genes whose expression was upregulated, we identified LMO1, which codes for an intertwining LIM-only factor involved in protein-DNA oligomeric complexes. By analysing its expression in Hox knockout mice, we show that Lmo1 is differentially regulated by Hoxa2 and Hoxb2, in specific columns of hindbrain neuronal progenitors. These results suggest that Lmo1 takes part in a Hox paralogue 2-dependent network regulating anteroposterior and dorsoventral hindbrain patterning.

Differential expression of LIM domain-only (LMO) genes in the developing mouse inner ear

The vertebrate inner ear, a complex sensory organ with vestibular and auditory functions, is derived from a single ectoderm structure called the otic placode. Currently, the molecular mechanisms governing the differentiation and specification of the otic epithelium are poorly understood. We present here a detailed expression study of LMO1-4 in the developing mouse inner ear using a combination of in situ hybridization and immunohistochemistry. LMO1 is specifically expressed in the vestibular and cochlear hair cells as well as the vestibular ganglia of the developing inner ear. LMO2 expression is detected in the periotic mesenchyme of the developing mouse cochlea from E12.5 to E14.5. The expression of LMO3 expression is first observed in the cochlea at E13.5 and becomes confined to the lesser epithelial ridge (LER) from E14.5 to E17.5. LMO3 is also expressed in some of the vestibular ganglion cells. LMO4 is initially expressed in the dorsolateral portion of the otic vesicle and its expression persists in the semicircular canals, macula, crista, and the spiral ganglia throughout embryogenesis. Thus, the regionalized expression patterns of LMO1-4 are closely associated with the morphogenesis of the inner ear.

LMO4 can interact with Smad proteins and modulate transforming growth factor-beta signaling in epithelial cells

LIM-only protein 4 (LMO4) plays critical roles in mammalian development, and has been proposed to play roles in epithelial oncogenesis, including breast cancer. As LMO4 is highly expressed in the epithelial compartments at locations of active mesenchymal-epithelial interactions, we reasoned that LMO4 might act by modulating signaling pathways involved in mesenchymal-epithelial signaling. One such candidate signal is the transforming growth factor-beta (TGFbeta) cytokine pathway, which plays important roles both in development and cancer. We show here that the transcriptional response to TGFbeta in epithelial cells is sensitive to LMO4 levels; both up- and downregulation of LMO4 can enhance TGFbeta signaling as assessed by a TGFbeta-responsive reporter gene. Furthermore, LMO4 can interact with the MH1 and linker domains of receptor-mediated Smad proteins, and associate with the endogenous TGFbeta-responsive Plasminogen Activator Inhibitor-1 gene promoter in a TGFbeta-dependent manner, suggesting that such interactions may mediate the effects of LMO4 on TGFbeta signaling. When introduced into mammary epithelial cells, LMO4 potentiated the growth-inhibitory effects of TGFbeta in those cells. These results define a new function for LMO4 as a coactivator in TGFbeta signaling, and provide a potential novel mechanism for LMO4-mediated regulation in development and oncogenesis.

Astrocyte heterogeneity revealed by expression of a GFAP-LacZ transgene

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein present primarily in astrocytes. The gene is first expressed as astrocytes mature, and in the adult is strongly upregulated in response to CNS damage. Thus, in addition to its astrocyte specificity, transcriptional regulation of the GFAP gene is of interest as a reporter of CNS signaling during development and injury. Several laboratories have shown that approximately 2 kb of 5'-flanking DNA of the human or mouse GFAP gene is sufficient to direct transgene expression to astrocytes and to confer developmental and injury-induced regulation. Enhancer regions have been identified adjacent to the basal promoter and about 1500 bp upstream of the RNA start site. Juxtaposition of these two segments yielded a 447 bp promoter, gfa28, which strongly drove reporter activity in transfected glioma cells. We report here that in mice a gfa28-lacZ transgene expresses in only certain brain regions, revealing an unexpected heterogeneity among astrocytes. The restricted pattern of expression is present early in development, is not altered by injury, and is preserved in cultured astrocytes. However, astrocytes cultured from an inactive region strongly express a transiently transfected gfa28-lacZ construct, and activity of the embedded gfa28-lacZ transgene is partially restored by treatment with a histone deacetylase inhibitor. These results indicate that the absence of gfa28-lacZ expression in specific brain regions results from a developmental failure to remodel GFAP chromatin to an open structure. Thus, expression of the gfa28-lacZ transgene appears to serendipitously mark a distinct set of astrocyte precursors.

Uniform Adherent Neural Progenitor Populations from Rhesus Embryonic Stem Cells

Rhesus and human embryonic stem cells (ESCs) are similar, making rhesus ESCs an appropriate preclinical allograft model for refining stem cell therapies. Use of rhesus ESC-derived neural progenitors (NPs) in preclinical applications will be enhanced if the neural derivation process is scalable and free from contaminating ESCs or nonneural cells. In this study, we have quantified temporal gene expression changes of rhesus ESC differentiated to uniform NPs using simple feeder-free adherent cultures. NPs exhibited a significant up-regulation of neural-specific genes and a downregulation of pluripotency genes. Additionally, expression of Hu, MAP2, and Tuj1, shows that NPs can form post-mitotic neurons. This study represents a simple and scalable means of producing adherent primate NPs for preclinical testing of neural cell-based therapy.

SCL, GATA-2 and Lmo2 expression in neurogenesis

SCL, Lmo2 and GATA factors form common transcription complexes during hematopoietic differentiation. The overlapping expression of SCL with GATA-2 and GATA-3 in the developing brain indicated that these factors might collaborate also in the course of neural tissue differentiation. The expression pattern of Lmo2 in the developing CNS, however, is not well understood. Here, we show that neural cells in the early embryonic chick mid- and hindbrain express SCL and GATA-2, while Lmo2 is expressed only in vascular elements. The lack of Lmo2 transcripts in neural cells demonstrated that SCL and GATA-2 cannot form common complexes with Lmo2 in the developing brain. In the course of neural tissue genesis, GATA-2 mRNA appeared prior to the SCL transcript. While GATA-2 expression decreased with maturation, SCL expression persisted at a high level also in post-neurogenic periods. The temporal pattern of SCL and GATA-2/3 expression was investigated also in vitro, in the course of induced neurogenesis by NE-4C neural stem cells. While GATA-2 expression increased from the very beginning of differentiation, SCL expression appeared only in more differentiated cells expressing proneural genes. GATA-3 expression, on the other hand, was detected only in advanced stages of the neuronal maturation, which were characterised by the activation of the Math2 neuronal gene. Similarly to the hematopoietic differentiation, GATA-2 expression precedes the activation of both SCL and GATA-3, and may play roles in the activation of the SCL gene in neuronal development. In contrast to hematopoietic differentiation, however, our results failed to demonstrate co-assembling of GATA factors or SCL with Lmo2. While overlapping expression of GATA-2/3 and SCL was detected, Lmo2 activation could not be demonstrated in neural cells in the investigated period of neuronal development.

Identification of novel differentially expressed genes in human astrocytomas by cDNA representational difference analysis

Diffuse infiltrating gliomas are the most common tumors of the central nervous system (CNS), naturally progressing from a lower-grade to a higher-grade malignancy. Several genetic alterations have been correlated with astrocytic tumors; however, a number of as yet unknown genes may also be involved. Therefore, we set out to search for genes that are differentially expressed in anaplastic astrocytoma and normal CNS tissue by applying a PCR-based subtractive hybridization approach, namely, representational difference analysis (RDA). The results of DNA sequencing of a sample (96 cDNA clones) from the subtracted library allowed the identification of 18 different genes, some of which were represented by several cDNA clones, coding for the Np95, LMO1, FCGBP, DSCAM, and taxilin proteins. Quantitative real-time PCR analysis for five of these genes was performed using samples of astrocytic tumors of different grades, confirming their higher expression when compared to non-tumoral CNS tissue. Identification of differentially expressed genes present in gliomas but not in normal CNS tissue is important not only to better understand the molecular basis of these cancers, but also to generate diagnostic DNA chips, which may be useful in future therapeutic intervention.

Lmo mutants reveal a novel role for circadian pacemaker neurons in cocaine-induced behaviors

Drosophila has been developed recently as a model system to investigate the molecular and neural mechanisms underlying responses to drugs of abuse. Genetic screens for mutants with altered drug-induced behaviors thus provide an unbiased approach to define novel molecules involved in the process. We identified mutations in the Drosophila LIM-only (LMO) gene, encoding a regulator of LIM-homeodomain proteins, in a genetic screen for mutants with altered cocaine sensitivity. Reduced Lmo function increases behavioral responses to cocaine, while Lmo overexpression causes the opposite effect, reduced cocaine responsiveness. Expression of Lmo in the principal Drosophila circadian pacemaker cells, the PDF-expressing ventral lateral neurons (LN(v)s), is sufficient to confer normal cocaine sensitivity. Consistent with a role for Lmo in LN(v)function,Lmomutants also show defects in circadian rhythms of behavior. However, the role for LN(v)s in modulating cocaine responses is separable from their role as pacemaker neurons: ablation or functional silencing of the LN(v)s reduces cocaine sensitivity, while loss of the principal circadian neurotransmitter PDF has no effect. Together, these results reveal a novel role for Lmo in modulating acute cocaine sensitivity and circadian locomotor rhythmicity, and add to growing evidence that these behaviors are regulated by shared molecular mechanisms. The finding that the degree of cocaine responsiveness is controlled by the Drosophila pacemaker neurons provides a neuroanatomical basis for this overlap. We propose that Lmo controls the responsiveness of LN(v)s to cocaine, which in turn regulate the flies' behavioral sensitivity to the drug.

Null mutation of the Lmo4 gene or a combined null mutation of the Lmo1/Lmo3 genes causes perinatal lethality, and Lmo4 controls neural tube development in mice

The LIM-only family of proteins comprises four members; two of these (LMO1 and LMO2) are involved in human T-cell leukemia via chromosomal translocations, and LMO2 is a master regulator of hematopoiesis. We have carried out gene targeting of the other members of the LIM-only family, viz., genes Lmo1, Lmo3 and Lmo4, to investigate their role in mouse development. None of these genes has an obligatory role in lymphopoiesis. In addition, while null mutations of Lmo1 or Lmo3 have no discernible phenotype, null mutation of Lmo4 alone causes perinatal lethality due to a severe neural tube defect which occurs in the form of anencephaly or exencephaly. Since the Lmo1 and Lmo3 gene sequences are highly related and have partly overlapping expression domains, we assessed the effect of compound Lmo1/Lmo3 null mutations. Although no anatomical defects were apparent in compound null pups, these animals also die within 24 h of birth, suggesting that a compensation between the related Lmo1 and 3 proteins can occur during embryogenesis to negate the individual loss of these genes. Our results complete the gene targeting of the LIM-only family in mice and suggest that all four members of this family are important in regulators of distinct developmental pathways.

Evidence for astrocyte heterogeneity: a distinct subpopulation of protoplasmic-like glial cells is detected in transgenic mice expressing Lmo1-lacZ

The adult mammalian central nervous system (CNS) contains a large number of different cell types, which arise from the ventricular (VZ) and subventricular zones during embryonic development. In this study, we used a transgenic mouse expressing Lmo1-LacZ from a randomly inserted promoter/reporter gene construct to identify a glial subpopulation. LMO1 is an LIM domain-containing protein, thought to act in protein-protein interactions. We found first that in the adult transgenic CNS, beta-galactosidase (beta-gal) was expressed in a specific subpopulation of protoplasmic-like cells, which did not express detectable levels of glial fibrilary acidic protein unless a lesion was produced. Secondly, during development, beta-gal(+) cells were found arising from discrete regions of the VZ. Taken together, these results identify a subpopulation of protoplasmic glial cells in the adult CNS and suggest that they arise from a restricted VZ region during CNS development.

Expression of the POU domain transcription factor, Oct-6, is attenuated in the adult mouse telencephalon, but increased by neurotoxic damage

Oct-6 is a POU III domain transcription factor expressed in embryonic stem cells, Schwann cells, and neuronal subpopulations during telencephalic development. Its role is unknown except in Schwann cells where it is thought to regulate myelin-specific gene expression. Expression of Oct-6 was recently discovered in neurons in postmortem human schizophrenic brain while being undetectable in matched controls. This study of human tissue contrasted in a number of regards with earlier studies of rodent brain and questioned what we can consider to be normal adult expression of this gene. In this study, we have investigated Oct-6 expression in normal adult mice and in mice treated with neuractive compounds. We show that Oct-6 is widely expressed in young adults but that its expression subsequently becomes restricted to specific neuronal subpopulations. Contrary to earlier reports, however, this specific expression is transient and is eventually completely lost from telencephalic neurons. The OCT-6 protein, somewhat surprisingly, is found to be cytoplasmic as well as nuclear in certain neuronal subpopulations. Finally, we report that neurotoxic doses of anticonvulsants reactivate OCT-6 expression in adult mouse brain.

The LIM-only protein, LMO4, and the LIM domain-binding protein, LDB1, expression in squamous cell carcinomas of the oral cavity

Carcinoma cells can lose their epithelial cell characteristics and dedifferentiate into a fibroblast-like cell during progression of a neoplasm. Aberrant expression of oligomeric transcriptional complexes contributes to progression of carcinomas. Although individual transcription factors initiating progression remain unknown, LIM-only protein (LMO) and LIM-domain binding protein (LDB) negatively regulate breast carcinoma cell differentiation. In this study, we investigated the expression of LMO4 and LDB in squamous cell carcinomas of the oral cavity. LMO4 mRNA was amplified in four of six carcinoma tissues and eight of 12 carcinoma cell lines, and LDB1 in three carcinoma tissues and 11 cell lines examined. Immunoprecipitation studies revealed that LMO4 and LDB1 interact with each other in the nuclear milieu of the carcinoma cells indicating the presence of an LMO4-LDB1-mediated transcription complex. Both LMO4 and LDB1 proteins were preferentially localised in the nuclei of carcinoma cells at the invasive front and the immunoreactivity was increased in less-differentiated carcinoma tissues (P<0.01). Carcinoma cells metastasised to the cervical lymph nodes with increased immunoreactivity compared to the primary site of neoplasm (P<0.05). These data suggest that the LMO4-LDB1 complexes may be involved in carcinoma progression possibly through dedifferentiation of squamous carcinoma cells of the oral cavity.

Single-cell transcriptional analysis of neuronal progenitors

The extraordinary cellular heterogeneity of the mammalian nervous system has largely hindered the molecular analysis of neuronal identity and diversity. In order to uncover mechanisms involved in neuronal differentiation and diversification, we have monitored the expression profiles of individual neurons and progenitor cells collected from dissociated tissue or captured from intact slices. We demonstrate that this technique provides a sensitive and reproducible representation of the single-cell transcriptome. In the olfactory system, hundreds of transcriptional differences were identified between olfactory progenitors and mature sensory neurons, enabling us to define the large variety of signaling pathways expressed by individual progenitors at a precise developmental stage. Finally, we show that regional differences in gene expression can be predicted from transcriptional analysis of single neuronal precursors isolated by laser capture from defined areas of the developing brain.

Dynamic spatiotemporal expression of LIM genes and cofactors in the embryonic and postnatal cerebral cortex

LIM-homeodomain (LIM-HD) genes encode a family of transcription factors known to be involved in development and patterning in several systems. Previously, we have shown that LIM-HD gene Lhx2 is required for the formation of a crucial boundary in the dorsal telencephalon (Bulchand et al. [2001] Mech Dev 100:165-175). To further explore the role of LIM-HD genes as well as the broader LIM gene family in dorsal telencephalic development, we examined the expression pattern of the members of this gene family and their cofactors in the developing mouse cerebral cortex. Transcription factor activity of the LIM-HD proteins requires the formation of a tetrameric complex consisting of two LIM-HD molecules linked by a dimer of cofactor (Clim) molecules. LIM-only (Lmo) proteins can interfere with this process by competing for the cofactors. LIM-HD protein function, thus, can be modulated by the presence of the appropriate Clim or Lmo molecules. At least 13 LIM-HD, 4 Lmo, and 2 Clim genes have been identified in the mouse. Several of these genes exhibit complex spatiotemporal patterns spanning different stages of cortical development, from embryonic to postnatal ages. Noteworthy features of the expression patterns include delineation of boundaries within the developing cortex, up- or down-regulation during formation of selected cortical layers, and a striking complementarity of expression of several members consistent with specific functions in cortical development. Significantly, in some cases, Lmo or Clim gene expression is robust where no LIM-HD gene expression is detectable. These results suggest multiple and distinct roles for LIM-HD, Lmo, and Clim genes in cortical development, and also support a LIM-HD-independent role for some Lmo and Clim members.

Developmental expression of serum response factor in the rat central nervous system

Serum response factor (SRF), a transcription factor known to be essential for early embryonic development as well as post-natal regulation of both cellular proliferation and myogenic differentiation, is expressed broadly in neurons within the adult mammalian central nervous system (CNS). The function of SRF within the developing CNS is not well established, but it is likely to play an important role in neuraxial development and neuronal function, since many of its known target genes (e.g., c-fos) and transcriptional partners (e.g., Elk-1) are also highly expressed in neurons. Immunohistochemical survey of the post-natal developing rat brain revealed a progressive increase in SRF immunoreactivity in neurons of the cerebral and cerebellar cortices, and in selective subcortical regions from birth (P0) through post-natal day 28 (P28). SRF immunoreactivity stabilized from P28 into adulthood. A few loci, such as the nucleus of cranial nerve VII, showed the reverse expression pattern (strong immunoreactivity at P0-P7, declining by P28). The developmental expression pattern of SRF overlaps significantly with that of myotonic dystrophy protein kinase, a potential upstream regulator, and of the LIM-only genes Lmo1, Lmo2 and Lmo3, whose products belong to a family of proteins known to be strong positive regulators of SRF's transcriptional activity. These data suggest that SRF has a significant function in the early post-natal development of the CNS.

Cerebral glucose utilization in transgenic mice overexpressing heat shock protein 70 is altered by dizocilpine

Heat shock protein (HSP70), a member of the 70 kDa HSP superfamily, has been widely implicated in the cellular stress response to numerous insults. HSP70 may be a significant factor in cell survival following stresses such as cerebral ischaemia. The precise mechanisms by which HSP70 facilitates cell survival remain unclear. The aim of this study was to ascertain whether any differences in local cerebral glucose utilization (LCGU) existed between transgenic mice overexpressing HSP70 (HSP70 Tg) and wild- type littermate (WT) mice. LCGU was assessed using (14)C-2-deoxyglucose in HSP70 Tg and WT mice under basal conditions (intraperitoneal injection of saline) and during metabolic activation produced by NMDA receptor blockade (intraperitoneal injection of dizocilpine, 1 mg/kg). No significant alterations in LCGU were observed between saline injected HSP70 Tg and WT mice in any of the 35 brain regions analyzed. Dizocilpine injection produced significant heterogeneous alterations in LCGU in HSP70 Tg mice (24 of 35 brain regions) and in WT mice (22 of 35 brain regions) compared with saline injected mice. The distribution of altered LCGU produced by dizocilpine was similar in HSP70 Tg and WT mice. However in five brain regions, dizocilpine injected HSP70 Tg mice displayed significantly altered LCGU compared to dizocilpine injected WT mice (anterior thalamic nucleus +27%, dorsal CA1 stratum lacunosum molecularae +22%, dorsal CA1 stratum oriens + 14%, superior olivary body -26%, and the nucleus of the lateral lemniscus -16%). These data highlight that while overexpression of HSP70 transgene does not significantly alter LCGU in the basal state, mice overexpressing the HSP70 transgene respond differently to metabolic stress produced by NMDA receptor blockade in some important brain regions.

Targeting expression of hsp70i to discrete neuronal populations using the Lmo-1 promoter: assessment of the neuroprotective effects of hsp70i in vivo and in vitro

Transgenic technology provides a powerful means of studying gene regulation and specific gene function with complex mammalian systems. In this study, the authors exploited the specific and discrete neuronal expression pattern mediated by promoter 1 of the Lmo-1 gene to study the neuroprotective effects of the inducible form of heat shock protein 70kD (hsp70i) in primary hippocampal cultures in a mouse model of global cerebral ischemia. Targeting expression of hsp70i to hippocampal neurons protected these cells significantly from toxic levels of glutamate and oxidative stress (for example, exposure to 10 micromol/L free iron produced a 26% increase in lactate dehydrogenase release from neurons cultured from wild-type mice, but a 7% increase in neurons cultured from hsp70i transgenic mice). Bilateral carotid occlusion (25 minutes) produced significantly less neuronal damage in the caudate nucleus and posterior thalamus in hsp70i transgenic mice than in wild-type littermates (for example, 21% +/- 9.3% and 12.5% +/- 9.0% neuronal damage in lateral caudate nucleus of wild-type and hsp70i transgenic mice, respectively, P < 0.05). The current study highlights the utility of targeted expression of transgenes of interest in cerebral ischemia and demonstrates that expression of hsp70i alone is sufficient to mediate the protection of primary neurons from denaturing stress and that expression of human hsp70i in vivo plays crucial role in determining the fate of neurons after ischemic challenge.

LIM-homeodomain gene Lhx2 regulates the formation of the cortical hem

We are interested in the early mechanisms that initiate regional patterning in the dorsal telencephalon, which gives rise to cerebral cortex. Members of the LIM-homeodomain (LIM-HD) family of transcription factors are implicated in patterning and cell fate specification in several systems including the mammalian forebrain. Mice in which Lhx2 is disrupted were reported to have reduced telencephalic development, and the hippocampal primordium appeared to be missing, by morphological observation. We hypothesized that this may be due to a defect in the cortical hem, a Wnt- and Bmp-rich putative signaling center in the medial telencephalon, a source of regulatory signals for hippocampal development. We asked if the expression of any known hem-specific signaling molecule is deficient in Lhx2-/- mice. Our results reveal, unexpectedly, that at embryonic day (E)12.5, what appears to be some spared 'lateral' cortex is instead an expanded cortical hem. Normally restricted to the extreme medial edge of the telencephalon, the hem covers almost the entire dorsal telencephalon in the Lhx2-/- mice. This indicates a role for Lhx2 in the regulation of the extent of the cortical hem. In spite of an expanded, mislocated hem in the Lhx2-/- telencephalon, a potential source of ectopic dorsalizing cues, no hippocampal differentiation is detected in tissue adjacent to the mutant hem, nor does the overall dorsoventral patterning appear perturbed. We propose that Lhx2 is involved at a crucial early step in patterning the telencephalon, where the neuroepithelium is first divided into presumptive cortical tissue, and the cortical hem. The defect in the Lhx2-/- telencephalon appears to be at this step.

Gene expression in the brain across the sleep-waking cycle

Sleep and waking differ significantly in terms of behavior, metabolism, and neuronal activity. Recent evidence indicates that sleep and waking also differ with respect to the expression of certain genes. To systematically investigate such changes, we used mRNA differential display and cDNA microarrays to screen approximately 10000 transcripts expressed in the cerebral cortex of rats after 8 h of sleep, spontaneous waking, or sleep deprivation. We found that 44 genes had higher mRNA levels after waking and/or sleep deprivation relative to sleep, while 10 were upregulated after sleep. Known genes that were upregulated in waking and sleep deprivation can be grouped into the following categories: immediate early genes/transcription factors (Arc, CHOP, IER5, NGFI-A, NGFI-B, N-Ras, Stat3), genes related to energy metabolism (glucose type I transporter Glut1, Vgf), growth factors/adhesion molecules (BDNF, TrkB, F3 adhesion molecule), chaperones/heat shock proteins (BiP, ERP72, GRP75, HSP60, HSP70), vesicle- and synapse-related genes (chromogranin C, synaptotagmin IV), neurotransmitter/hormone receptors (adrenergic receptor alpha(1A) and beta(2), GABA(A) receptor beta(3), glutamate NMDA receptor 2A, glutamate AMPA receptor GluR2 and GluR3, nicotinic acetylcholine receptor beta(2), thyroid hormone receptor TRbeta), neurotransmitter transporters (glutamate/aspartate transporter GLAST, Na(+)/Cl(-) transporter NTT4/Rxt1), enzymes (aryl sulfotransferase, c-jun N-terminal kinase 1, serum/glucocorticoid-induced serine/threonine kinase), and a miscellaneous group (calmodulin, cyclin D2, LMO-4, metallothionein 3). Several other genes that were upregulated in waking and all the genes upregulated in sleep, with the exception of the one coding for membrane protein E25, did not match any known sequence. Thus, significant changes in gene expression occur across behavioral states, which are likely to affect basic cellular functions such as RNA and protein synthesis, neural plasticity, neurotransmission, and metabolism.

Zinc-enriched (ZEN) terminals in mouse olfactory bulb

The present study was designed to localize zinc-enriched (ZEN) terminals in mouse olfactory bulb by means of ZnT3 immunocytochemistry (ICC) and zinc autometallography (AMG). The immunocytochemical staining of ZnT3 was closely correlated with the AMG pattern. ZEN terminals were defined as terminals showing both ZnT3 immunoreactivities and AMG granules. At the light microscopic level, dense staining patterns for ZnT3 immunoreactivity were seen in the granule cell layer and the olfactory glomerular layer. At the ultrastructural level, ZEN terminals were restricted to presynaptic terminals with single or multiple postsynaptic thickenings. The postsynaptic profiles contacting ZEN terminals appeared to be dendrites or somata of granule cells in the granule cell layer and periglomerular cells and mitral/tufted (M/T) cells in the olfactory glomerular layer. This suggests that two main sources of ZEN terminals are present in mouse olfactory bulb: (1) centrifugal fibres making asymmetrical synapses with granule cells and periglomerular cells, and (2) olfactory receptor terminals contacting dendritic profiles of M/T cells or periglomerular cells. The close correlation between ZEN terminals and the glutamatergic system is discussed.

The LIM domain: regulation by association

The LIM domain is a zinc finger structure that is present in several types of proteins, including homeodomain transcription factors, kinases and proteins that consist of several LIM domains. Proteins containing LIM domains have been discovered to play important roles in a variety of fundamental biological processes including cytoskeleton organization, cell lineage specification and organ development, but also for pathological functions such as oncogenesis, leading to human disease. The LIM domain has been demonstrated to be a protein-protein interaction motif that is critically involved in these processes. The recent isolation and analysis of more LIM domain-containing proteins from several species have confirmed and broadened our knowledge about LIM protein function. Furthermore, the identification and characterization of factors that interact with LIM domains illuminates mechanisms of combinatorial developmental regulation.