Differential response of calmodulin genes in the mouse brain after systemic kainate administration

YB-1 binds to GluR2 mRNA and CaM1 mRNA in the brain and regulates their translational levels in an activity-dependent manner

The translational regulator YB-1 binds to mRNAs. In the brain, YB-1 is prominently expressed from the prenatal stage until the first week after birth, being associated with polysomes and distributed in neuronal dendrites, but its expression declines to a much lower level thereafter. It is therefore of interest to identify the mRNAs whose translation is controlled by YB-1 in the postnatal growing brain. In this study we found that YB-1 interacted with the mRNAs for glutamate receptor subunit 2 (GluR2) and calmodulin1 (CaM1) in both brain and NG108-15 cells. Overexpression or knockdown of YB-1 altered the levels of these proteins significantly in cultured cells without any change in their mRNA levels. When the cells were treated with neurotransmitters, translation of these proteins was induced within a short time, and a change in the amount of YB-1 on its target mRNAs was observed in the heavy-sedimenting polysome fractions on a sucrose gradient. Depletion of YB-1 expression by siRNA abrogated the translational activation. Furthermore, in the brain of kainic acid-treated mice, the distribution of YB-1 was shifted to much heavier fractions associated with polysomes within 30 min to 1 h after the treatment, and the distribution returned to lighter fractions within the following 2 h. The protein levels of GluR2 and CaM1 were also increased transiently when the distribution of YB-1 on the gradient changed. These results suggest that in the brain of growing mice, YB-1 binds to GluR2 and CaM1 mRNAs and regulates their translation in an activity-dependent manner.

Ontogeny of calmodulin gene expression in rat brain

Calmodulin (CaM), a multifunctional intracellular calcium receptor, is a key element in signaling mechanisms. It is encoded in vertebrates by multiple apparently redundant genes (CaM I, II, III). To investigate whether differential expression takes place in the developing rat brain, a quantitative in situ hybridization analysis was carried out involving 15 brain areas at six ages between embryonic day 19 and postnatal day 20 (PD20) with gene-specific [(35)S]cRNA probes. A widespread, developmental stage-specific and differential expression of the three CaM genes was observed. The characteristic changes in the CaM mRNA levels in the examined time frame allowed the brain regions to be classified into three categories. For the majority of the areas (e.g. the piriform cortex for CaM III), the signal intensities peaked at around PD10 and the expression profile was symmetric (type 1). Other regions (e.g. the cerebral cortex, layer 1 for CaM II) displayed their highest signal intensities at the earliest age measured, followed by a gradual decrease (type 2). The signal intensities in the regions in the third group (e.g. the hypothalamus for CaM III) fluctuated from age to age (type 3). Marked CaM mRNA levels were measured for each transcript corresponding to the three CaM genes in the molecular layers of the cerebral and cerebellar cortici and hippocampus, suggesting their dendritic translocation. The highest signal intensity was measured for CaM II mRNA, followed by those for CaM III and CaM I mRNAs on PD1. However, the CaM II and CaM III mRNAs subsequently decreased steeply, while the CaM I mRNAs were readily detected even on PD20. Our results suggest that during development (1) the transcription of the CaM genes is under differential, area-specific control, and (2) a large population of CaM mRNAs is targeted to the dendritic compartment in a gene-specific manner.

Differential calmodulin gene expression in the rodent brain

Apparently redundant members of the calmodulin (CaM) gene family encode for the same amino acid sequence. CaM, a ubiquitous cytoplasmic calcium ion receptor, regulates the function of a variety of target molecules even in a single cell. Maintenance of the fidelity of the active CaM-target interactions in different compartments of the cell requires a rather complex control of the total cellular CaM pool comprising multiple levels of regulatory circuits. Among these mechanisms, it has long been proposed that a multigene family maximizes the regulatory potentials at the level of the gene expression. CaM genes are expressed at a particularly profound level in the mammalian central nervous system (CNS), especially in the highly polarized neurons. Thus, in the search for clear evidence of the suggested differential expression of the CaM genes, much of the research has been focused on the elements of the CNS. This review aims to give a comprehensive survey on the current understanding of this field at the level of the regulation of CaM mRNA transcription and distribution in the rodent brain. The results indicate that the CaM genes are indeed expressed in a gene-specific manner in the developing and adult brain under physiological conditions. To establish local CaM pools in distant intracellular compartments (dendrites and glial processes), local protein synthesis from differentially targeted mRNAs is also employed. Moreover, the CaM genes are controlled in a unique, gene-specific fashion when responding to certain external stimuli. Additionally, putative regulatory elements have been identified on the CaM genes and mRNAs.

Role of calmodulin in the differentiation/activation of microglial cells

In the present work the role of calmodulin (CaM) in regulating lipopolysaccharide (LPS)-induced microglial activation and in the spontaneous microglial differentiation has been investigated. We used pure rat microglial cell cultures to examine the effects of W13, a specific inhibitor of CaM, on microglial activation produced by LPS and the effect of CaM inhibition on microglial proliferation induced by the macrophage colony-stimulating factor (M-CSF). Microglial morphological transformation, inducible nitric oxide synthase (iNOS) activity and proliferating cell nuclear antigen (PCNA) immunostaining were determinate. Results show that CaM does not participate in the microglial increase of iNOS produced by LPS. In contrast, it is involved in spontaneous microglial ramification and in the activation of proliferation from quiescence. Multiple second-messenger pathways are involved in the transduction of signals initiated by LPS. The study of these mechanisms may allow us to extend our knowledge of the signals controlling the expression of these mediators.

The Ca2+/calmodulin system in neuronal hyperexcitability

Calmodulin (CaM) is a major Ca2+-binding protein in the brain, where it plays an important role in the neuronal response to changes in the intracellular Ca2+ concentration. Calmodulin modulates numerous Ca2+-dependent enzymes and participates in relevant cellular functions. Among the different CaM-binding proteins, the Ca2+/CaM dependent protein kinase II and the phosphatase calcineurin are especially important in the brain because of their abundance and their participation in numerous neuronal functions. Therefore, the role of the Ca2+/CaM signalling system in different neurotoxicological or neuropathological conditions associated to alterations in the intracellular Ca2+ concentration is a subject of interest. We here report different evidences showing the involvement of CaM and the CaM-binding proteins above mentioned in situations of neuronal hyperexcitability induced by convulsant agents. Signal transduction pathways mediated by specific CaM binding proteins warrant future study as potential targets in the development of new drugs to inhibit convulsant responses or to prevent or attenuate the alterations in neuronal function associated to the deleterious increases in the intracellular Ca2+ levels described in different pathological situations.

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.

Multiple calmodulin genes exhibit systematically differential responses to chronic ethanol treatment and withdrawal in several regions of the rat brain

Ethanol induces profound alterations in the neuronal signaling systems, including the calcium (Ca(2+)) signaling. Prolonged exposure to ethanol evokes adaptive changes in the affected systems as they strive to restore the normal neuronal function. We investigated the involvement of calmodulin (CaM) genes, coding for the major mediator protein of intracellular Ca(2+) signals, in these adaptive processes at the mRNA level. The changes induced in the regional abundances of the CaM I, II, and III mRNA classes by chronic ethanol treatment and withdrawal were examined by means of quantitative in situ hybridization, employing gene-specific [35S]cRNA probes on rat brain cryostat sections. Regional analysis of the resulting changes in mRNA levels highlighted brain areas that belong in neuronal systems known to be especially sensitive to the action of ethanol. The results revealed systematically differential regulation for the three mRNA classes: the CaM I and CaM III mRNA levels displayed increases, and CaM II levels decreases in the affected brain regions, in both chronic ethanol- and withdrawal-treated animals. As regards the numbers of brain regions undergoing significant alterations in mRNA content, the CaM I mRNA levels exhibited changes in most brain areas, the CaM II levels did so in a lower number of brain regions, and the CaM III levels changed in only a few brain areas. These results suggest a differential regulation for the CaM genes in the rat brain and may help towards elucidation of the functional significance of the multiple CaM genes in the mammalian genome.

Differential regulation of calmodulin content and calmodulin messenger RNA levels by acute and repeated, intermittent amphetamine in dopaminergic terminal and midbrain areas

Repeated doses of psychoactive drugs often produce adaptive responses that differ from the initial drug application and additional adaptive processes occur following cessation of the drug. The relationship between alterations in calmodulin protein and messenger RNA produced by an initial versus a repeated dose of amphetamine was examined, as well as changes following drug cessation. Calmodulin protein and messenger RNA of the three individual calmodulin genes were measured in rat dopaminergic cell body and terminal areas following acute or repeated amphetamine. Rats were either injected once with 2.5mg/kg amphetamine or saline and decapitated after 3h, or given 10 injections of amphetamine three to four days apart and decapitated 3h after the final injection. Calmodulin messenger RNA and protein were also measured three and seven days after ceasing drug treatment. Acute amphetamine increased calmodulin 1.7-fold in the striatum and threefold in the ventral mesencephalon, with corresponding elevations in calmodulin messenger RNAs. In response to the 10th dose of amphetamine, however, the degree of increase in calmodulin was diminished in the striatum and ablated in the ventral mesencephalon. Correspondingly, select species of calmodulin messenger RNA were decreased from control levels. In the frontal cortex or nucleus accumbens, calmodulin levels were basically unaltered by the first or 10th doses of amphetamine, but both calmodulin and its messenger RNA were altered with time upon cessation of the drug. Three days later, both calmodulin protein and messenger RNA were decreased in select brain areas. By seven days after the 10th injection, calmodulin content was altered compared to saline controls in all areas, but the change in messenger RNA no longer paralleled the change in protein.Our findings demonstrate that both calmodulin protein and select species of calmodulin messenger RNA are altered by acute amphetamine, but this effect is attenuated after repeated, intermittent amphetamine. There are further time-dependent changes after cessation of repeated amphetamine, which may reflect compensatory neuronal responses. The alterations in calmodulin content and synthesis could contribute to changes in patterns or duration of behaviors that occur upon cessation of repeated amphetamine.

The calmodulin multigene family as a unique case of genetic redundancy: multiple levels of regulation to provide spatial and temporal control of calmodulin pools?

Calmodulin (CaM) is a ubiquitous, highly conserved calcium sensor protein involved in the regulation of a wide variety of cellular events. In vertebrates, an identical CaM protein is encoded by a family of non-allelic genes, raising questions concerning the evolutionary pressure responsible for the maintenance of this apparently redundant family. Here we review the evidence that the control of the spatial and temporal availability of CaM may require multiple regulatory levels to ensure the proper localization, maintenance and size of intracellular CaM pools. Differential transcription of the CaM genes provides one level of regulation to meet tissue-specific, developmental and cell-specific needs for altered CaM levels. Post-transcriptional regulation occurs at the level of mRNA stability, perhaps dependent on alternative polyadenylation and differences in the untranslated sequences of the multiple gene transcripts. Recent evidence indicates that trafficking of specific CaM mRNAs may occur to specialized cellular locales such as the dendrites of neurons. This could allow local CaM synthesis and thereby help generate local pools of CaM. Local CaM activity may be further regulated by post-translational mechanisms such as phosphorylation or storage of CaM in a 'masked' form. The spatial resolution of CaM activity is enhanced by the limited free diffusion of CaM combined with differential affinity for and availability of target proteins. Preserving multiple CaM genes with divergent noncoding sequences may be necessary in complex organisms to ensure that the many CaM-dependent processes occur with the requisite spatial and temporal resolution. Transgenic mouse models and studies on mice carrying single and double gene 'knockouts' promise to shed further light on the role of specificity versus redundancy in the evolutionary maintenance of the vertebrate CaM multigene family.

Water deprivation upregulates the three calmodulin genes in exclusively the supraoptic nucleus of the rat brain

Calmodulin (CaM), the ubiquitous intracellular calcium-binding protein, is coded by three bona fide CaM genes (CaM I, CaM II and CaM III) in mammals. They code for the same protein and are transcribed at particularly high levels in the brain, where CaM plays an essential role in basic neuronal functions. In this study, the expression of the three CaM genes in response to osmotic stimuli by water deprivation was investigated in the rat brain, with particular interest as concerns the hypothalamic magnocellular nuclei. CaM mRNA levels were determined by quantitative in situ hybridization autoradiography with gene-specific [35S]cRNA probes. In response to osmotic challenge, it was found that upregulation of the three CaM genes participates in the activation of the hypothalamo-hypophyseal system in the supraoptic nucleus (SON) (126% to 169%), but not in the magnocellular part of the paraventricular hypothalamic nucleus (PVN) (-10%). CaM mRNA levels decreased by 10%-15% in the suprachiasmatic nucleus (SCh) and many other extrahypothalamic brain areas. The opposite responses of the CaM gene expression in the SON and the magnocellular part of the PVN suggest a functional difference between them. Moreover, the significantly different magnitudes of the changes in the CaM mRNA levels in the SON nucleus (138%, 126% and 169% for CaM I, CaM II and CaM III, respectively) exemplify the precise differential control of the CaM gene expression in the brain.

Sustained potentiation of AP1 DNA binding is not always associated with neuronal death following systemic administration of kainic acid in murine hippocampus

Mice were intraperitoneally injected with kainic acid (KA), followed by dissection of frozen coronal sections and subsequent punching out of the pyramidal and granular cell layers in the hippocampus under a binocular microscope. Systemic administration of KA resulted in marked and sustained potentiation of binding of a radiolabeled double stranded oligonucleotide probe for the nuclear transcription factor activator protein-1 (AP1) in the pyramidal cell layers of the CA1 and CA3 subfields and the granule cell layers of the dentate gyrus 2-18 h later. Morphological evaluation using cresyl violet revealed marked losses of neuronal layers in the pyramidal CA1 and CA3 subfields, but not in the granular dentate gyrus, within 6 weeks after administration. Supershift analysis using antibodies against different Jun and Fos family members differentiated between AP1 DNA binding in hippocampal nuclear extracts obtained 2 and 18 h after the administration of KA. These results suggest that neuronal death may not always follow modulation of de novo synthesis of particular proteins through sustained potentiation of AP1 DNA binding which involves expression of different Jun and Fos family members in response to systemic administration of KA in murine hippocampus.

The Ca2+/calmodulin signaling system in the neural response to excitability. Involvement of neuronal and glial cells

Ca2+ plays a critical role in the normal function of the central nervous system. However, it can also be involved in the development of different neuropathological and neurotoxicological processes. The processing of a Ca2+ signal requires its union with specific intracellular proteins. Calmodulin is a major Ca(2+)-binding protein in the brain, where it modulates numerous Ca(2+)-dependent enzymes and participates in relevant cellular functions. Among the different calmodulin-binding proteins, the Ca2+/calmodulin-dependent protein kinase II and the phosphatase calcineurin are especially important in the brain because of their abundance and their participation in numerous neuronal functions. We present an overview on different works aimed at the study of the Ca2+/calmodulin signalling system in the neural response to convulsant agents. Ca2+ and calmodulin antagonists inhibit the seizures induced by different convulsant agents, showing that the Ca2+/calmodulin signalling system plays a role in the development of the seizures induced by these agents. Processes occurring in association with seizures, such as activation of c-fos, are not always sensitive to calmodulin, but depend on the convulsant agent considered. We characterized the pattern of expression of the three calmodulin genes in the brain of control mice and detected alterations in specific areas after inducing seizures. The results obtained are in favour of a differential regulation of these genes. We also observed alterations in the expression of the Ca2+/calmodulin-dependent protein kinase II and calcineurin after inducing seizures. In addition, we found that reactive microglial cells increase the expression of calmodulin and Ca2+/calmodulin-dependent protein kinase II in the brain after seizures.

Differential distribution and intracellular targeting of mRNAs corresponding to the three calmodulin genes in rat brain. A quantitative in situ hybridization study

To investigate the pattern of expression of the three calmodulin (CaM) genes by in situ hybridization, gene-specific [35S]-cRNA probes complementary to the multiple CaM mRNAs were hybridized in rat brain sections and subsequently detected by quantitative film or high-resolution nuclear emulsion autoradiography. A widespread and differential area-specific distribution of the CaM mRNAs was detected. The expression patterns corresponding to the three CaM genes differed most considerably in the olfactory bulb, the cerebral and cerebellar cortices, the diagonal band, the suprachiasmatic and medial habenular nuclei, and the hippocampus. Moreover, the significantly higher CaM I and CaM III mRNA copy numbers than that of CaM II in the molecular layers of certain brain areas revealed a differential dendritic targeting of these mRNAs. The results indicate a differential pattern of distribution of the multiple CaM mRNAs at two levels of cellular organization in the brain: (a) region-specific expression and (b) specific intracellular targeting. A precise and gene-specific regulation of synthesis and distribution of CaM mRNAs therefore exists under physiological conditions in the rat brain.

Alterations in calmodulin mRNA expression and calmodulin content in rat brain after repeated, intermittent amphetamine

To assess whether calmodulin (CaM) gene expression could have a role in behavioral sensitization induced by repeated, intermittent amphetamine, CaM protein and mRNA of the three separate CaM genes were measured in several different brain areas from rats repeatedly administered saline or amphetamine. Rats were injected twice weekly for five weeks, followed by one week of withdrawal. CaM protein and mRNA were measured in dorsal striatum, limbic forebrain, prefrontal cortex, ventral mesencephalon and piriform cortex. There were increases of CaM protein content and decreases of CaM I mRNA in the dorsal striatum and prefrontal cortex. CaM II mRNA was also decreased in the dorsal striatum. A decrease of CaM protein and an increase of CaM I mRNA were found in the ventral mesencephalon. There was no change of CaM protein in the limbic forebrain, although a decrease of CaM I mRNA was detected. CaM protein and mRNA were not altered in the piriform cortex. Our findings demonstrate that both CaM content and mRNA are altered after an amphetamine regimen leading to sensitization. The fact that the changes in CaM content and mRNA are in dopaminergic brain areas associated with sensitization suggests that CaM could contribute to neurochemical events underlying behavioral sensitization to amphetamine.

Characterization of the human CALM2 calmodulin gene and comparison of the transcriptional activity of CALM1, CALM2 and CALM3

Human calmodulin is encoded by three genes CALM1, CALM2 and CALM3 located on different chromosomes. To complete the characterization of this family, the exon-intron structure of CALM2 was solved by a combination of genomic DNA library screening and genomic PCR amplification. Intron interruptions were found at identical positions in human CALM2 as in CALM1 and CALM3; however, the overall size of CALM2 (16 kb) was almost twice that of the other two human CALM genes. Over 1 kb of the 5' flanking sequence of human CALM2 were determined, revealing the presence of a TATA-like sequence 27 nucleotides upstream of the transcriptional start site and several conserved sequence elements possibly involved in the regulation of this gene. To determine if differential transcriptional activity plays a major role in regulating cellular calmodulin levels, we directly measured and compared the mRNA abundance and transcriptional activity of the three CALM genes in proliferating human teratoma cells. CALM3 was at least 5-fold more actively transcribed than CALM1 or CALM2. CALM transcriptional activity agreed well with the mRNA abundance profile in the teratoma cells. In transient transfections using luciferase reporter genes driven by 1 kb of the 5' flanking DNA of the three CALM genes, the promoter activity correlated with the endogenous CALM transcriptional activity, but only when the 5' untranslated regions were included in the constructs. We conclude that the CALM gene family is differentially active at the transcriptional level in teratoma cells and that the 5' untranslated regions are necessary to recover full promoter activation.

Calmodulin is expressed by reactive microglia in the hippocampus of kainic acid-treated mice

Calmodulin is a calcium-binding protein that is highly abundant in the brain, where it is involved in many essential functions. The protein is mainly expressed by neuronal cells. Calmodulin is encoded by three different genes in mammals, all of them producing an identical protein. Alterations in the expression of either calmodulin genes or protein have been reported in the rodent brain by several authors in different experimental situations. However, no mention has been made to date of possible alterations in calmodulin expression in glial cells in response to certain stimuli. In the present study, we found an increase in the expression of calmodulin in reactive microglial cells in the mouse hippocampus 24 h after an intraperitoneal administration of a convulsant dose of kainic acid. The results show that a high expression of calmodulin can be added to the list of changes described to occur in microglial cells when they become reactive microglia in response to certain kinds of stimuli, in contrast to the non-detectable level of expression of this protein observed in the resting microglial cells. It is difficult to explain such an increase due to the great number of processes in which calmodulin is involved, but the great level of calmodulin observed in the reactive microglial cells shows that calmodulin immunolabelling can be used to reveal these kinds of cells.