Non-cell-autonomous regulation of interneuron specification mediated by extracellular vesicles

Disruption in neurogenesis and neuronal migration can influence the assembly of cortical circuits, affecting the excitatory-inhibitory balance and resulting in neurodevelopmental and neuropsychiatric disorders. Using ventral cerebral organoids and dorsoventral cerebral assembloids with mutations in the extracellular matrix gene LGALS3BP, we show that extracellular vesicles released into the extracellular environment regulate the molecular differentiation of neurons, resulting in alterations in migratory dynamics. To investigate how extracellular vesicles affect neuronal specification and migration dynamics, we collected extracellular vesicles from ventral cerebral organoids carrying a mutation in LGALS3BP, previously identified in individuals with cortical malformations and neuropsychiatric disorders. These results revealed differences in protein composition and changes in dorsoventral patterning. Proteins associated with cell fate decision, neuronal migration, and extracellular matrix composition were altered in mutant extracellular vesicles. Moreover, we show that treatment with extracellular vesicles changes the transcriptomic profile in neural progenitor cells. Our results indicate that neuronal molecular differentiation can be influenced by extracellular vesicles.

Tripartite extended amygdala-basal ganglia CRH circuit drives locomotor activation and avoidance behavior

An adaptive stress response involves various mediators and circuits orchestrating a complex interplay of physiological, emotional, and behavioral adjustments. We identified a population of corticotropin-releasing hormone (CRH) neurons in the lateral part of the interstitial nucleus of the anterior commissure (IPACL), a subdivision of the extended amygdala, which exclusively innervate the substantia nigra (SN). Specific stimulation of this circuit elicits hyperactivation of the hypothalamic-pituitary-adrenal axis, locomotor activation, and avoidance behavior contingent on CRH receptor type 1 (CRHR1) located at axon terminals in the SN, which originate from external globus pallidus (GPe) neurons. The neuronal activity prompting the observed behavior is shaped by IPACL^CRH and GPe^CRHR1 neurons coalescing in the SN. These results delineate a previously unidentified tripartite CRH circuit functionally connecting extended amygdala and basal ganglia nuclei to drive locomotor activation and avoidance behavior.

Cell-Type-Specific Impact of Glucocorticoid Receptor Activation on the Developing Brain: A Cerebral Organoid Study

OBJECTIVE

A fine-tuned balance of glucocorticoid receptor (GR) activation is essential for organ formation, with disturbances influencing many health outcomes. In utero, glucocorticoids have been linked to brain-related negative outcomes, with unclear underlying mechanisms, especially regarding cell-type-specific effects. An in vitro model of fetal human brain development, induced human pluripotent stem cell (hiPSC)-derived cerebral organoids, was used to test whether cerebral organoids are suitable for studying the impact of prenatal glucocorticoid exposure on the developing brain.

METHODS

The GR was activated with the synthetic glucocorticoid dexamethasone, and the effects were mapped using single-cell transcriptomics across development.

RESULTS

The GR was expressed in all cell types, with increasing expression levels through development. Not only did its activation elicit translocation to the nucleus and the expected effects on known GR-regulated pathways, but also neurons and progenitor cells showed targeted regulation of differentiation- and maturation-related transcripts. Uniquely in neurons, differentially expressed transcripts were significantly enriched for genes associated with behavior-related phenotypes and disorders. This human neuronal glucocorticoid response profile was validated across organoids from three independent hiPSC lines reprogrammed from different source tissues from both male and female donors.

CONCLUSIONS

These findings suggest that excessive glucocorticoid exposure could interfere with neuronal maturation in utero, leading to increased disease susceptibility through neurodevelopmental processes at the interface of genetic susceptibility and environmental exposure. Cerebral organoids are a valuable translational resource for exploring the effects of glucocorticoids on early human brain development.

Extracellular LGALS3BP regulates neural progenitor position and relates to human cortical complexity

Basal progenitors (BPs), including intermediate progenitors and basal radial glia, are generated from apical radial glia and are enriched in gyrencephalic species like humans, contributing to neuronal expansion. Shortly after generation, BPs delaminate towards the subventricular zone, where they further proliferate before differentiation. Gene expression alterations involved in BP delamination and function in humans are poorly understood. Here, we study the role of LGALS3BP, so far known as a cancer biomarker, which is a secreted protein enriched in human neural progenitors (NPCs). We show that individuals with LGALS3BP de novo variants exhibit altered local gyrification, sulcal depth, surface area and thickness in their cortex. Additionally, using cerebral organoids, human fetal tissues and mice, we show that LGALS3BP regulates the position of NPCs. Single-cell RNA-sequencing and proteomics reveal that LGALS3BP-mediated mechanisms involve the extracellular matrix in NPCs' anchoring and migration within the human brain. We propose that its temporal expression influences NPCs' delamination, corticogenesis and gyrification extrinsically.

GNG5 Controls the Number of Apical and Basal Progenitors and Alters Neuronal Migration During Cortical Development

Cortical development is a very complex process in which any temporal or spatial alterations can give rise to a wide range of cortical malformations. Among those malformations, periventricular heterotopia (PH) is characterized by clusters of neurons that do not migrate to the correct place. Cerebral organoids derived from patients with mutations in DCHS1 and FAT4, which have been associated with PH, exhibit higher levels of GNG5 expression in a patient-specific cluster of neurons. Here we investigate the role of GNG5 during the development of the cerebral cortex in mice and human cerebral organoids. GNG5, highly expressed in progenitors and downregulated in neurons, is critical for controlling the number of apical and basal progenitors and neuronal migration. Moreover, forced expression of GNG5 recapitulates some of the alterations observed upon downregulation of Dchs1 and Fat4 in mice and human cerebral organoids derived from DCHS1 and FAT4 patients, suggesting a critical role of GNG5 in cortical development.

Cross Talk at the Cytoskeleton-Plasma Membrane Interface: Impact on Neuronal Morphology and Functions

The cytoskeleton and its associated proteins present at the plasma membrane not only determine the cell shape but also modulate important aspects of cell physiology such as intracellular transport including secretory and endocytic pathways. Continuous remodeling of the cell structure and intense communication with extracellular environment heavily depend on interactions between cytoskeletal elements and plasma membrane. This review focuses on the plasma membrane-cytoskeleton interface in neurons, with a special emphasis on the axon and nerve endings. We discuss the interaction between the cytoskeleton and membrane mainly in two emerging topics of neurobiology: (i) production and release of extracellular vesicles and (ii) local synthesis of new proteins at the synapses upon signaling cues. Both of these events contribute to synaptic plasticity. Our review provides new insights into the physiological and pathological significance of the cytoskeleton-membrane interface in the nervous system.

NR2F1 regulates regional progenitor dynamics in the mouse neocortex and cortical gyrification in BBSOAS patients

The relationships between impaired cortical development and consequent malformations in neurodevelopmental disorders, as well as the genes implicated in these processes, are not fully elucidated to date. In this study, we report six novel cases of patients affected by BBSOAS (Boonstra‐Bosch‐Schaff optic atrophy syndrome), a newly emerging rare neurodevelopmental disorder, caused by loss‐of‐function mutations of the transcriptional regulator NR2F1. Young patients with NR2F1 haploinsufficiency display mild to moderate intellectual disability and show reproducible polymicrogyria‐like brain malformations in the parietal and occipital cortex. Using a recently established BBSOAS mouse model, we found that Nr2f1 regionally controls long‐term self‐renewal of neural progenitor cells via modulation of cell cycle genes and key cortical development master genes, such as Pax6. In the human fetal cortex, distinct NR2F1 expression levels encompass gyri and sulci and correlate with local degrees of neurogenic activity. In addition, reduced NR2F1 levels in cerebral organoids affect neurogenesis and PAX6 expression. We propose NR2F1 as an area‐specific regulator of mouse and human brain morphology and a novel causative gene of abnormal gyrification.

Cystatin B is essential for proliferation and interneuron migration in individuals with EPM1 epilepsy

Progressive myoclonus epilepsy (PME) of Unverricht–Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder with the highest incidence of PME worldwide. Mutations in the gene encoding cystatin B (CSTB) are the primary genetic cause of EPM1. Here, we investigate the role of CSTB during neurogenesis in vivo in the developing mouse brain and in vitro in human cerebral organoids (hCOs) derived from EPM1 patients. We find that CSTB (but not one of its pathological variants) is secreted into the mouse cerebral spinal fluid and the conditioned media from hCOs. In embryonic mouse brain, we find that functional CSTB influences progenitors’ proliferation and modulates neuronal distribution by attracting interneurons to the site of secretion via cell‐non‐autonomous mechanisms. Similarly, in patient‐derived hCOs, low levels of functional CSTB result in an alteration of progenitor's proliferation, premature differentiation, and changes in interneurons migration. Secretion and extracellular matrix organization are the biological processes particularly affected as suggested by a proteomic analysis in patients’ hCOs. Overall, our study sheds new light on the cellular mechanisms underlying the development of EPM1.

ECE2 regulates neurogenesis and neuronal migration during human cortical development

During embryonic development, excitatory projection neurons migrate in the cerebral cortex giving rise to organised layers. Periventricular heterotopia (PH) is a group of aetiologically heterogeneous disorders in which a subpopulation of newborn projection neurons fails to initiate their radial migration to the cortex, ultimately resulting in bands or nodules of grey matter lining the lateral ventricles. Although a number of genes have been implicated in its cause, currently they only satisfactorily explain the pathogenesis of the condition for 50% of patients. Novel gene discovery is complicated by the extreme genetic heterogeneity recently described to underlie its cause. Here, we study the neurodevelopmental role of endothelin‐converting enzyme‐2 (ECE2) for which two biallelic variants have been identified in two separate patients with PH. Our results show that manipulation of ECE2 levels in human cerebral organoids and in the developing mouse cortex leads to ectopic localisation of neural progenitors and neurons. We uncover the role of ECE2 in neurogenesis, and mechanistically, we identify its involvement in the generation and secretion of extracellular matrix proteins in addition to cytoskeleton and adhesion.

Granulins Regulate Aging Kinetics in the Adult Zebrafish Telencephalon

Granulins (GRN) are secreted factors that promote neuronal survival and regulate inflammation in various pathological conditions. However, their roles in physiological conditions in the brain remain poorly understood. To address this knowledge gap, we analysed the telencephalon in Grn-deficient zebrafish and identified morphological and transcriptional changes in microglial cells, indicative of a pro-inflammatory phenotype in the absence of any insult. Unexpectedly, activated mutant microglia shared part of their transcriptional signature with aged human microglia. Furthermore, transcriptome profiles of the entire telencephali isolated from young Grn-deficient animals showed remarkable similarities with the profiles of the telencephali isolated from aged wildtype animals. Additionally, 50% of differentially regulated genes during aging were regulated in the telencephalon of young Grn-deficient animals compared to their wildtype littermates. Importantly, the telencephalon transcriptome in young Grn-deficent animals changed only mildly with aging, further suggesting premature aging of Grn-deficient brain. Indeed, Grn loss led to decreased neurogenesis and oligodendrogenesis, and to shortening of telomeres at young ages, to an extent comparable to that observed during aging. Altogether, our data demonstrate a role of Grn in regulating aging kinetics in the zebrafish telencephalon, thus providing a valuable tool for the development of new therapeutic approaches to treat age-associated pathologies.

The Aryl Hydrocarbon Receptor Pathway Defines the Time Frame for Restorative Neurogenesis

Zebrafish have a high capacity to replace lost neurons after brain injury. New neurons involved in repair are generated by a specific set of glial cells, known as ependymoglial cells. We analyze changes in the transcriptome of ependymoglial cells and their progeny after injury to infer the molecular pathways governing restorative neurogenesis. We identify the aryl hydrocarbon receptor (AhR) as a regulator of ependymoglia differentiation toward post-mitotic neurons. In vivo imaging shows that high AhR signaling promotes the direct conversion of a specific subset of ependymoglia into post-mitotic neurons, while low AhR signaling promotes ependymoglial proliferation. Interestingly, we observe the inactivation of AhR signaling shortly after injury followed by a return to the basal levels 7 days post injury. Interference with timely AhR regulation after injury leads to aberrant restorative neurogenesis. Taken together, we identify AhR signaling as a crucial regulator of restorative neurogenesis timing in the zebrafish brain.

Cystatin B Involvement in Synapse Physiology of Rodent Brains and Human Cerebral Organoids

Cystatin B (CSTB) is a ubiquitous protein belonging to a superfamily of protease inhibitors. CSTB may play a critical role in brain physiology because its mutations cause progressive myoclonic epilepsy-1A (EPM1A), the most common form of progressive myoclonic epilepsy. However, the molecular mechanisms underlying the role of CSTB in the central nervous system (CNS) are largely unknown. To investigate the possible involvement of CSTB in the synaptic plasticity, we analyzed its expression in synaptosomes as a model system in studying the physiology of the synaptic regions of the CNS. We found that CSTB is not only present in the synaptosomes isolated from rat and mouse brain cortex, but also secreted into the medium in a depolarization-controlled manner. In addition, using biorthogonal noncanonical amino acid tagging (BONCAT) procedure, we demonstrated, for the first time, that CSTB is locally synthesized in the synaptosomes. The synaptic localization of CSTB was confirmed in a human 3D model of cortical development, namely cerebral organoids. Altogether, these results suggest that CSTB may play a role in the brain plasticity and open a new perspective in studying the involvement of CSTB deregulation in neurodegenerative and neuropsychiatric diseases.

Fluorescence-Activated Cell Sorting-Based Isolation and Characterization of Neural Stem Cells from the Adult Zebrafish Telencephalon

Adult mammalian brain, including humans, has rather limited addition of new neurons and poor regenerative capacity. In contrast, neural stem cells (NSC) with glial identity and neurogenesis are highly abundant throughout the adult zebrafish brain. Importantly, the activation of NSC and production of new neurons in response to injuries lead to the brain regeneration in zebrafish brain. Therefore, understanding of the molecular pathways regulating NSC behavior in response to injury is crucial in order to set the basis for experimental modification of these pathways in glial cells after injury in the mammalian brain and to elicit neuronal regeneration. Here, we describe the procedure that we successfully used to prospectively isolate NSCs from adult zebrafish telencephalon, extract RNA, and prepare cDNA libraries for next generation sequencing (NGS) and full transcriptome analysis as the first step toward understanding regulatory mechanisms leading to restorative neurogenesis in zebrafish. Moreover, we describe an alternative approach to analyze antigenic properties of NSC in the adult zebrafish brain using intracellular fluorescence activated cell sorting (FACS). We employ this method to analyze the number of proliferating NSCs positive for proliferating cell nuclear antigen (PCNA) in the prospectively isolated population of stem cells.

Reactive oxygen species and glutathione antioxidants in the testis of the soil biosentinel Podarcis sicula (Rafinesque 1810)

Important toxicological achievements have been made during the last decades using reptiles. We focus our investigation on gonadal reproductive health of the soil biosentinel Podarcis sicula which is very sensitive to endocrine-disrupting chemicals. The aim of this study is to quantitatively detect, by sensitive microassays, reactive oxygen species and the glutathione antioxidants in the testis and investigate if they are differentially expressed before and after remediation of a site of the "Land of Fires" (Campania, Italy) subject to illicit dumping of unknown material. The oxidative stress level was evaluated by electron spin resonance spectroscopy applying a spin-trapping procedure able to detect products of lipid peroxidation, DNA damage and repair by relative mobility shift, and poly(ADP-ribose) polymerase enzymatic activity, respectively, the expression of glutathione peroxidase 4 transcript by real-time quantitative PCR analysis, the antioxidant glutathione S-transferase, a well-assessed pollution index, by enzymatic assay and the total soluble antioxidant capacity. Experimental evidences from the different techniques qualitatively agree, thus confirming the robustness of the combined experimental approach. Collected data, compared to those from a reference unpolluted site constitute evidence that the reproductive health of this lizard is impacted by pollution exposure. Remediation caused significant reduction of reactive oxygen species and downregulation of glutathione peroxidase 4 mRNAs in correspondence of reduced levels of glutathione S-transferase, increase of antioxidant capacity, and repair of DNA integrity. Taken together, our results indicate directions to define new screening approaches in remediation assessment.

RNA interference machinery-mediated gene regulation in mouse adult neural stem cells

Background

Neurogenesis in the brain of adult mammals occurs throughout life in two locations: the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. RNA interference mechanisms have emerged as critical regulators of neuronal differentiation. However, to date, little is known about its function in adult neurogenesis.

Results

Here we show that the RNA interference machinery regulates Doublecortin levels and is associated with chromatin in differentiating adult neural progenitors. Deletion of Dicer causes abnormal higher levels of Doublecortin. The microRNA pathway plays an important role in Doublecortin regulation. In particular miRNA-128 overexpression can reduce Doublecortin levels in differentiating adult neural progenitors.

Conclusions

We conclude that the RNA interference components play an important role, even through chromatin association, in regulating neuron-specific gene expression programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0198-7) contains supplementary material, which is available to authorized users.

Neurodevelopment. Live imaging of adult neural stem cell behavior in the intact and injured zebrafish brain

Adult neural stem cells are the source for restoring injured brain tissue. We used repetitive imaging to follow single stem cells in the intact and injured adult zebrafish telencephalon in vivo and found that neurons are generated by both direct conversions of stem cells into postmitotic neurons and via intermediate progenitors amplifying the neuronal output. We observed an imbalance of direct conversion consuming the stem cells and asymmetric and symmetric self-renewing divisions, leading to depletion of stem cells over time. After brain injury, neuronal progenitors are recruited to the injury site. These progenitors are generated by symmetric divisions that deplete the pool of stem cells, a mode of neurogenesis absent in the intact telencephalon. Our analysis revealed changes in the behavior of stem cells underlying generation of additional neurons during regeneration.

Expression analysis of five zebrafish RXFP3 homologues reveals evolutionary conservation of gene expression pattern

Relaxin peptides exert different functions in reproduction and neuroendocrine processes via interaction with two evolutionarily unrelated groups of receptors: RXFP1 and RXFP2 on one hand, RXFP3 and RXFP4 on the other hand. Evolution of receptor genes after splitting of tetrapods and teleost lineage led to a different retention rate between mammals and fish, with the latter having more gene copies compared to the former. In order to improve our knowledge on the evolution of the relaxin ligands/receptors system and have insights on their function in early stages of life, in the present paper we analyzed the expression pattern of five zebrafish RXFP3 homologue genes during embryonic development. In our analysis, we show that only two of the five genes are expressed during embryogenesis and that their transcripts are present in all the developmental stages. Spatial localization analysis of these transcripts revealed that the gene expression is restricted in specific territories starting from early pharyngula stage. Both genes are expressed in the brain but in different cell clusters and in extra-neural territories, one gene in the interrenal gland and the other in the pancreas. These two genes share expression territories with the homologue mammalian counterpart, highlighting a general conservation of gene expression regulatory processes and their putative function during evolution that are established early in vertebrate embryogenesis.

Developmental expression pattern of two zebrafish rxfp3 paralogue genes

In mammals, the RXFP3 is the cognate receptor of the relaxin-3 peptide (RLN3). In teleosts, many different orthologue genes for RXFP3 are present. In particular, two paralogue genes, rxfp3-2a and rxfp3-2b, likely encode the receptors for the Rln3a peptide. The transcription of these two rxfp3 genes is differentially regulated early during zebrafish embryogenesis. Indeed, reverse transcription-polymerase chain reaction analyses show that the rxfp3-2b transcript is always present during embryo development, while the rxfp3-2a transcript is detectable only at larval stage. By in situ hybridization experiments on embryos and larvae, the rxfp3-2b transcript was revealed in the brain and in the retinal ganglion cell layer and thymus. Particularly in the brain, many territories are involved in the rxfp3-2b expression, among them the optic tectum, thalamus, preoptic area, different nerve nuclei, habenula and pineal gland. The RXFP3 spatiotemporal expression pattern appears to be conserved between Danio rerio and mammals, as also previously showed for the corresponding ligand, the RLN3. Interestingly, the brain areas expressing the rxfp3-2b receptor gene are involved in the visual system, emotional behaviors and circadian rhythm and could be functionally related to the neurotransmitter Rln3a-expressing territories.

Characterization and developmental expression pattern of the relaxin receptor rxfp1 gene in zebrafish

We report the gene characterization, the cDNA cloning and the temporal and spatial expression pattern of the relaxin receptor rxfp1 gene in the zebrafish Danio rerio. The zebrafish rxfp1 gene has the same syntenic genomic organization, and a similar exon-intron structure to the homologue human gene. Furthermore, the deduced Rxfp1 protein sequence shows a high degree of amino acid similarity when compared with the human protein and the conservation of all amino acid identity necessary for the binding with relaxin. Our results show that rxfp1 gene is active either during embryogenesis or in the adult organism, showing a wide expression pattern. Moreover, we provide the first description of rxfp1 spatial expression pattern during embryo development, showing that the transcript is already present at the early developmental stage and is distributed in all of the embryonic cells until somitogenesis. Starting at the pharyngula stage the gene expression becomes mainly restricted in the brain territories. In fact, at the larval stage, the transcript is detectable in the epiphysis, postoptic region, posterior tuberculum, hypothalamus, optic tectum, tegmentum/pons, medulla and also in the structure of a peripheral nervous system, the terminal nerve. The rxfp1 expression pattern in Danio rerio embryos is very similar to that reported in the adult mammalian brain, suggesting a pivotal role of this receptor in the neurophysiology processes already at very early developmental stages.

Evidence of genetic instability in tumors and normal nearby tissues

BACKGROUND

Comprehensive analyses have recently been performed on many human cancer tissues, leading to the identification of a number of mutated genes but providing no information on the variety of mutations present in each of them. This information is of interest to understand the possible origin of gene mutations that cause tumors.

METHODOLOGY/PRINCIPAL FINDINGS

We have analyzed the sequence heterogeneity of the transcripts of the human HPRT and G6PD single copy genes that are not considered tumor markers. Analyses have been performed on different colon cancers and on the nearby histologically normal tissues of two male patients. Several copies of each cDNA, which were produced by cloning the RT-PCR-amplified fragments of the specific mRNA, have been sequenced. Similar analyses have been performed on blood samples of two ostensibly healthy males as reference controls. The sequence heterogeneity of the HPRT and G6PD genes was also determined on DNA from tumor tissues. The employed analytical approach revealed the presence of low-frequency mutations not detectable by other procedures. The results show that genetic heterogeneity is detectable in HPRT and G6PD transcripts in both tumors and nearby healthy tissues of the two studied colon tumors. Similar frequencies of mutations are observed in patient genomic DNA, indicating that mutations have a somatic origin. HPRT transcripts show genetic heterogeneity also in healthy individuals, in agreement with previous results on human T-cells, while G6PD transcript heterogeneity is a characteristic of the patient tissues. Interestingly, data on TP53 show little, if any, heterogeneity in the same tissues.

CONCLUSIONS/SIGNIFICANCE

These findings show that genetic heterogeneity is a peculiarity not only of cancer cells but also of the normal tissue where a tumor arises.

Cystatin B and its EPM1 mutants are polymeric and aggregate prone in vivo

Progressive myoclonus epilepsy type 1 (EPM1) is a neurodegenerative disease correlating with mutations of the cystatin B gene. Cystatin B is described as a monomeric protein with antiprotease function. This work shows that, in vivo, cystatin B has a polymeric structure, highly resistant to SDS, urea, boiling and sensitive to reducing agents and alkaline pH. Hydrogen peroxide increases the polymeric structure of the protein. Mass spectrometry analysis shows that the only component of the polymers is cystatin B. EPM1 mutants of cystatin B transfected in cultured cells are also polymeric. The banding pattern generated by a cysteine-minus mutant is different from that of the wild-type protein as it contains only monomers, dimers and some very high MW bands while misses components of MW intermediate between 25 and 250 kDa. Overexpression of wild-type or EPM1 mutants of cystatin B in neuroblastoma cells generates cytoplasmic aggregates. The cysteine-minus mutant is less prone to the formation of inclusion bodies. We conclude that cystatin B in vivo has a polymeric structure sensitive to the redox environment and that overexpression of the protein generates aggregates. This work describes a protein with a physiological role characterized by highly stable polymers prone to aggregate formation in vivo.

A possible flip-flop genetic mechanism for reciprocal gene expression

Innexins are a family of transmembrane proteins involved in the formation of gap junctions, specific intercellular channels, in invertebrates. Analyses of the entire innexin family during Drosophila melanogaster embryonic development shows the occurrence of complex and specific patterns of expression of the different genes. Innexins inx-2 and inx-7, in general, do not appear to exhibit extensive co-expression in different D. melanogaster cellular compartments. We propose here a new and robust mechanism, based on our analysis of the genomic organization of inx-2 and inx-7, that structurally justifies the reciprocal expression of genes.

Cell-specific expression of the epm1 (cystatin B) gene in developing rat cerebellum

Cystatin B (cystB) is an anti-protease implicated in EPM1, a degenerative disease of the central nervous system. This work analyzes the pattern of expression of cystB in developing and adult cerebellum, identifying the cystB positive cells by double immune-fluorescence microscopy using specific cell markers. In primary glial cells, cystB is found in progenitor and differentiated oligodendrocytes as well as in astrocytes. In the cerebellum, only oligodendrocyte progenitors express cystB. In myelin-producing cells, cystB synthesis is strongly down-regulated and the protein is not detectable. Astrocytes and Bergmann glia express cystB at all the developmental stages analyzed both in the cell body and in the fibers. Most neurons of developing and adult rat cerebellum do not express detectable amounts of cystB, with the exception of the Purkinje cells and of some cells of the differentiated molecular layer. In human cerebellum, cystB is present in Purkinje cells and Bergmann glial fibers only. cystB is also found in the cortical neurons of the dentate gyrus of the hippocampus. In rat cerebellum, cystB forms a complex with a number of proteins, two of which are specific to the nervous system. The cellular co-localization of cystB and its partners in developing and adult cerebellum is also shown.

The expression of de novo DNA methylase DNMT3b, of the methyl-CpG binding protein MBD2b and of 5-MCDG glycosylase shows two waves of induction during CaCO-2 cell differentiation

DNA methylation plays a central role in the control of gene expression during development and cell differentiation, thus DNA methylation and demethylation processes are expected to be strictly regulated during these events. We have explored the expression levels of the genes encoding DNA methylases, methyl-CpG binding proteins and demethylases during in vitro differentiation of human carcinoma colon cells (CaCO-2) used as a model system. The results show that the global DNA methylation pattern remains constant during CaCO-2 cells differentiation indicating that required genome methylation pattern in cell differentiation was already established in the seeded cells. On the contrary, the timing of expression of several of the explored genes is tightly regulated, suggesting they are involved in the regulation of the differentiation program. In particular, the timing of expression of DNMT3b and of MBD2b and 5-MCDG shows two peaks not observed in the time courses of the expression of other genes belonging to the same families. These events, not dependent on the cell cycle synchronization, have apparently no significant impact on the overall methylation status of the genome.

New insights into the molecular basis of progressive myoclonus epilepsy: a multiprotein complex with cystatin B

Cystatin B is an anti-proteolytic polypeptide implicated in progressive myoclonus epilepsy (EPM1), a degenerative disease of the central nervous system. The knock-out mouse model of the disease shows apoptosis of the cerebellar granule cells. We have identified five recombinant proteins interacting with cystatin B and none of them is a protease. We show that three of these proteins (RACK-1, beta-spectrin and NF-L) co-immunoprecipitate with cystatin B in rat cerebellum. Confocal immunofluorescence analysis shows that the same proteins are present in the granule cells of developing cerebellum, as well as in Purkinje cells of adult rat cerebellum. We propose that a cystatin B multiprotein complex has a specific cerebellar function and that the loss of this function might contribute to the disease in EPM1 patients.