NECABs: a family of neuronal Ca(2+)-binding proteins with an unusual domain structure and a restricted expression pattern

Glucocorticoid receptor-NECAB1 axis can negatively regulate insulin secretion in pancreatic β-cells

The mechanisms of impaired glucose-induced insulin secretion from the pancreatic β-cells in obesity have not yet been completely elucidated. Here, we aimed to assess the effects of adipocyte-derived factors on the functioning of pancreatic β-cells. We prepared a conditioned medium using 3T3-L1 cell culture supernatant collected at day eight (D8CM) and then exposed the rat pancreatic β-cell line, INS-1D. We found that D8CM suppressed insulin secretion in INS-1D cells due to reduced intracellular calcium levels. This was mediated by the induction of a negative regulator of insulin secretion-NECAB1. LC-MS/MS analysis results revealed that D8CM possessed steroid hormones (cortisol, corticosterone, and cortisone). INS-1D cell exposure to cortisol or corticosterone increased Necab1 mRNA expression and significantly reduced insulin secretion. The increased expression of Necab1 and reduced insulin secretion effects from exposure to these hormones were completely abolished by inhibition of the glucocorticoid receptor (GR). NECAB1 expression was also increased in the pancreatic islets of db/db mice. We demonstrated that the upregulation of NECAB1 was dependent on GR activation, and that binding of the GR to the upstream regions of Necab1 was essential for this effect. NECAB1 may play a novel role in the adipoinsular axis and could be potentially involved in the pathophysiology of obesity-related diabetes mellitus.

Autism-Risk Gene necab2 Regulates Psychomotor and Social Behavior as a Neuronal Modulator of mGluR1 Signaling

Background

De novo deletion of the neuronal calcium-binding protein 2 (NECAB2) locus is associated with idiopathic autism spectrum disorders (ASDs). The in vivo function of NECAB2 in the brain remains largely elusive.

Methods

We investigated the morphological and behavioral profiles of both necab2 knock-out and overexpression zebrafish models. The expression pattern and molecular role of necab2 were probed through a combination of in vitro and in vivo assays.

Results

We show that Necab2 is a neuronal specific, cytoplasmic, and membrane-associated protein, abundantly expressed in the telencephalon, habenula, and cerebellum. Necab2 is distributed peri-synaptically in subsets of glutamatergic and GABAergic neurons. CRISPR/Cas9-generated necab2 knock-out zebrafish display normal morphology but exhibit a decrease in locomotor activity and thigmotaxis with impaired social interaction only in males. Conversely, necab2 overexpression yields behavioral phenotypes opposite to the loss-of-function. Proteomic profiling uncovers a role of Necab2 in modulating signal transduction of G-protein coupled receptors. Specifically, co-immunoprecipitation, immunofluorescence, and confocal live-cell imaging suggest a complex containing NECAB2 and the metabotropic glutamate receptor 1 (mGluR1). In vivo measurement of phosphatidylinositol 4,5-bisphosphate further substantiates that Necab2 promotes mGluR1 signaling.

Conclusions

Necab2 regulates psychomotor and social behavior via modulating a signaling cascade downstream of mGluR1.

Apolipoprotein E4 Effects a Distinct Transcriptomic Profile and Dendritic Arbor Characteristics in Hippocampal Neurons Cultured in vitro

The APOE gene is diversified by three alleles ε2, ε3, and ε4 encoding corresponding apolipoprotein (apo) E isoforms. Possession of the ε4 allele is signified by increased risks of age-related cognitive decline, Alzheimer's disease (AD), and the rate of AD dementia progression. ApoE is secreted by astrocytes as high-density lipoprotein-like particles and these are internalized by neurons upon binding to neuron-expressed apoE receptors. ApoE isoforms differentially engage neuronal plasticity through poorly understood mechanisms. We examined here the effects of native apoE lipoproteins produced by immortalized astrocytes homozygous for ε2, ε3, and ε4 alleles on the maturation and the transcriptomic profile of primary hippocampal neurons. Control neurons were grown in the presence of conditioned media from Apoe -/- astrocytes. ApoE2 and apoE3 significantly increase the dendritic arbor branching, the combined neurite length, and the total arbor surface of the hippocampal neurons, while apoE4 fails to produce similar effects and even significantly reduces the combined neurite length compared to the control. ApoE lipoproteins show no systemic effect on dendritic spine density, yet apoE2 and apoE3 increase the mature spines fraction, while apoE4 increases the immature spine fraction. This is associated with opposing effects of apoE2 or apoE3 and apoE4 on the expression of NR1 NMDA receptor subunit and PSD95. There are 1,062 genes differentially expressed across neurons cultured in the presence of apoE lipoproteins compared to the control. KEGG enrichment and gene ontology analyses show apoE2 and apoE3 commonly activate expression of genes involved in neurite branching, and synaptic signaling. In contrast, apoE4 cultured neurons show upregulation of genes related to the glycolipid metabolism, which are involved in dendritic spine turnover, and those which are usually silent in neurons and are related to cell cycle and DNA repair. In conclusion, our work reveals that lipoprotein particles comprised of various apoE isoforms differentially regulate various neuronal arbor characteristics through interaction with neuronal transcriptome. ApoE4 produces a functionally distinct transcriptomic profile, which is associated with attenuated neuronal development. Differential regulation of neuronal transcriptome by apoE isoforms is a newly identified biological mechanism, which has both implication in the development and aging of the CNS.

Thalamus mediates neocortical Down state transition via GABAB-receptor-targeting interneurons

Slow-wave sleep is characterized by near-synchronous alternation of active Up states and quiescent Down states in the neocortex. Although the cortex itself can maintain these oscillations, the full expression of Up-Down states requires intact thalamocortical circuits. Sensory thalamic input can drive the cortex into an Up state. Here we show that midline thalamic neurons terminate Up states synchronously across cortical areas. Combining local field potential, single-unit, and patch-clamp recordings in conjunction with optogenetic stimulation and silencing in mice in vivo, we report that thalamic input mediates Down transition via activation of layer 1 neurogliaform inhibitory neurons acting on GABA_B receptors. These results strengthen the evidence that thalamocortical interactions are essential for the full expression of slow-wave sleep, show that Down transition is an active process mediated by cortical GABA_B receptors, and demonstrate that thalamus synchronizes Down transitions across cortical areas during natural slow-wave sleep.

NECAB1 and NECAB2 are Prevalent Calcium-Binding Proteins of CB1/CCK-Positive GABAergic Interneurons

The molecular repertoire of the "Ca2+-signaling toolkit" supports the specific kinetic requirements of Ca2+-dependent processes in different neuronal types. A well-known example is the unique expression pattern of calcium-binding proteins, such as parvalbumin, calbindin, and calretinin. These cytosolic Ca2+-buffers control presynaptic and somatodendritic processes in a cell-type-specific manner and have been used as neurochemical markers of GABAergic interneuron types for decades. Surprisingly, to date no typifying calcium-binding proteins have been found in CB1 cannabinoid receptor/cholecystokinin (CB1/CCK)-positive interneurons that represent a large population of GABAergic cells in cortical circuits. Because CB1/CCK-positive interneurons display disparate presynaptic and somatodendritic Ca2+-transients compared with other interneurons, we tested the hypothesis that they express alternative calcium-binding proteins. By in silico data mining in mouse single-cell RNA-seq databases, we identified high expression of Necab1 and Necab2 genes encoding N-terminal EF-hand calcium-binding proteins 1 and 2, respectively, in CB1/CCK-positive interneurons. Fluorescent in situ hybridization and immunostaining revealed cell-type-specific distribution of NECAB1 and NECAB2 throughout the isocortex, hippocampal formation, and basolateral amygdala complex. Combination of patch-clamp electrophysiology, confocal, and STORM super-resolution microscopy uncovered subcellular nanoscale differences indicating functional division of labor between the two calcium-binding proteins. These findings highlight NECAB1 and NECAB2 as predominant calcium-binding proteins in CB1/CCK-positive interneurons.

Postnatal Developmental Expression Profile Classifies the Indusium Griseum as a Distinct Subfield of the Hippocampal Formation

The indusium griseum (IG) is a cortical structure overlying the corpus callosum along its anterior–posterior extent. It has been classified either as a vestige of the hippocampus or as an extension of the dentate gyrus via the fasciola cinerea, but its attribution to a specific hippocampal subregion is still under debate. To specify the identity of IG neurons more precisely, we investigated the spatiotemporal expression of calbindin, secretagogin, Necab2, PCP4, and Prox1 in the postnatal mouse IG, fasciola cinerea, and hippocampus. We identified the calcium-binding protein Necab2 as a first reliable marker for the IG and fasciola cinerea throughout postnatal development into adulthood. In contrast, calbindin, secretagogin, and PCP4 were expressed each with a different individual time course during maturation, and at no time point, IG or fasciola cinerea principal neurons expressed Prox1, a transcription factor known to define dentate granule cell fate. Concordantly, in a transgenic mouse line expressing enhanced green fluorescent protein (eGFP) in dentate granule cells, neurons of IG and fasciola cinerea were eGFP-negative. Our findings preclude that IG neurons represent dentate granule cells, as earlier hypothesized, and strongly support the view that the IG is an own hippocampal subfield composed of a distinct neuronal population.

Detailed neuronal distribution of GPR3 and its co-expression with EF-hand calcium-binding proteins in the mouse central nervous system

The G-protein coupled receptor 3 (GPR3), a member of the class A rhodopsin-type GPR family, constitutively activates Gαs proteins without any ligands. Although there have been several reports concerning the functions of GPR3 in neurons, the physiological roles of GPR3 have not been fully elucidated. To address this issue, we analyzed GPR3 distribution in detail using fluorescence-based X-gal staining in heterozygous GPR3 knockout/LacZ knock-in mice, and further investigated the types of GPR3-expressing neurons using fluorescent double labeling with various EF-hand Ca²⁺-binding proteins. In addition to the previously reported GPR3-expressing areas, we identified GPR3 expression in the basal ganglia and in many nuclei of the cranial nerves, in regions related to olfactory, auditory, emotional, and motor functions. In addition, GPR3 was not only observed in excitatory neurons in layer V of the cerebral cortex, the CA2 region of the hippocampus, and the lateral nucleus of the thalamus, but also in γ-aminobutyric acid (GABA)-ergic interneurons in the cortex, hippocampus, thalamus, striatum, and cerebellum. GPR3 was frequently co-expressed with neuronal Ca²⁺-binding protein 2 (NECAB2) in neurons in various regions of the central nervous system, especially in the hippocampal CA2, medial habenular nucleus, lateral thalamic nucleus, dorsolateral striatum, brainstem, and spinal cord anterior horn. Furthermore, GPR3 also co-localized with NECAB2 at the tips of neurites in differentiated PC12 cells. These results suggest that GPR3 and NECAB2 are highly co-expressed in specific neurons, and that GPR3 may modulate Ca²⁺ signaling by interacting with NECAB2 in specific areas of the central nervous system.

PKCγ interneurons, a gateway to pathological pain in the dorsal horn

Chronic pain is a frequent and disabling condition that is significantly maintained by central sensitization, which results in pathological amplification of responses to noxious and innocuous stimuli. As such, mechanical allodynia, or pain in response to a tactile stimulus that does not normally provoke pain, is a cardinal feature of chronic pain. Recent evidence suggests that the dorsal horn excitatory interneurons that express the γ isoform of protein kinase C (PKCγ) play a critical role in the mechanism of mechanical allodynia during chronic pain. Here, we review this evidence as well as the main aspects of the development, anatomy, electrophysiology, inputs, outputs, and pathophysiology of dorsal horn PKCγ neurons. Primary afferent high-threshold neurons transmit the nociceptive message to the dorsal horn of the spinal cord and trigeminal system where it activates second-order nociceptive neurons relaying the information to the brain. In physiological conditions, low-threshold mechanoreceptor inputs activate inhibitory interneurons in the dorsal horn, which may control activation of second-order nociceptive neurons. During chronic pain, low-threshold mechanoreceptor inputs now activate PKCγ neurons that forward the message to second-order nociceptive neurons, turning thus tactile inputs into pain. Several mechanisms may contribute to opening this gate, including disinhibition, activation of local astrocytes, release of diffusible factors such as reactive oxygen species, and alteration of the descending serotoninergic control on PKCγ neurons through 5-HT_2A serotonin receptors. Dorsal horn PKCγ neurons, therefore, appear as a relevant therapeutic target to alleviate mechanical allodynia during chronic pain.

Behavioral defects associated with amygdala and cortical dysfunction in mice with seeded α-synuclein inclusions

Parkinson’s disease (PD) is defined by motor symptoms such as tremor at rest, bradykinesia, postural instability, and stiffness. In addition to the classical motor defects that define PD, up to 80% of patients experience cognitive changes and psychiatric disturbances, referred to as PD dementia (PDD). Pathologically, PD is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and intracellular inclusions, called Lewy bodies and Lewy neurites, composed mostly of α-synuclein. Much of PD research has focused on the role of α-synuclein aggregates in degeneration of SNpc dopamine neurons because of the impact of loss of striatal dopamine on the classical motor phenotypes. However, abundant Lewy pathology is also found in other brain regions including the cortex and limbic brain regions such as the amygdala, which may contribute to non-motor phenotypes. Little is known about the consequences of α-synuclein inclusions in these brain regions, or in neuronal subtypes other than dopamine neurons. This project expands knowledge on how α-synuclein inclusions disrupt behavior, specifically non-motor symptoms of synucleinopathies. We show that bilateral injections of fibrils into the striatum results in robust bilateral α-synuclein inclusion formation in the cortex and amygdala. Inclusions in the amygdala and prefrontal cortex primarily localize to excitatory neurons, but unbiased stereology shows no significant loss of neurons in the amygdala or cortex. Fibril injected mice show defects in a social dominance behavioral task and fear conditioning, tasks that are associated with prefrontal cortex and amygdala function. Together, these observations suggest that seeded α-synuclein inclusion formation impairs behaviors associated with cortical and amygdala function, without causing cell loss, in brain areas that may play important roles in the complex cognitive features of PDD

GABAergic Medial Septal Neurons with Low-Rhythmic Firing Innervating the Dentate Gyrus and Hippocampal Area CA3

The medial septum implements cortical theta oscillations, a 5–12 Hz rhythm associated with locomotion and paradoxical sleep reflecting synchronization of neuronal assemblies such as place cell sequence coding. Highly rhythmic burst-firing parvalbumin-positive GABAergic medial septal neurons are strongly coupled to theta oscillations and target cortical GABAergic interneurons, contributing to coordination within one or several cortical regions. However, a large population of medial septal neurons of unidentified neurotransmitter phenotype and with unknown axonal target areas fire with a low degree of rhythmicity. We investigated whether low-rhythmic-firing neurons (LRNs) innervated similar or different cortical regions to high-rhythmic-firing neurons (HRNs) and assessed their temporal dynamics in awake male mice. The majority of LRNs were GABAergic and parvalbumin-immunonegative, some expressing calbindin; they innervated interneurons mostly in the dentate gyrus (DG) and CA3. Individual LRNs showed several distinct firing patterns during immobility and locomotion, forming a parallel inhibitory stream for the modulation of cortical interneurons. Despite their fluctuating firing rates, the preferred firing phase of LRNs during theta oscillations matched the highest firing probability phase of principal cells in the DG and CA3. In addition, as a population, LRNs were markedly suppressed during hippocampal sharp-wave ripples, had a low burst incidence, and several of them did not fire on all theta cycles. Therefore, CA3 receives GABAergic input from both HRNs and LRNs, but the DG receives mainly LRN input. We propose that distinct GABAergic LRNs contribute to changing the excitability of the DG and CA3 during memory discrimination via transient disinhibition of principal cells.

SIGNIFICANCE STATEMENT For the encoding and recall of episodic memories, nerve cells in the cerebral cortex are activated in precisely timed sequences. Rhythmicity facilitates the coordination of neuronal activity and these rhythms are detected as oscillations of different frequencies such as 5–12 Hz theta oscillations. Degradation of these rhythms, such as through neurodegeneration, causes memory deficits. The medial septum, a part of the basal forebrain that innervates the hippocampal formation, contains high- and low-rhythmic-firing neurons (HRNs and LRNs, respectively), which may contribute differentially to cortical neuronal coordination. We discovered that GABAergic LRNs preferentially innervate the dentate gyrus and the CA3 area of the hippocampus, regions important for episodic memory. These neurons act in parallel with the HRNs mostly via transient inhibition of inhibitory neurons.

Ca2+-binding protein NECAB2 facilitates inflammatory pain hypersensitivity

Pain signals are transmitted by multisynaptic glutamatergic pathways. Their first synapse between primary nociceptors and excitatory spinal interneurons gates the sensory load. In this pathway, glutamate release is orchestrated by Ca2+-sensor proteins, with N-terminal EF-hand Ca2+-binding protein 2 (NECAB2) being particular abundant. However, neither the importance of NECAB2+ neuronal contingents in dorsal root ganglia (DRGs) and spinal cord nor the function determination by NECAB2 has been defined. A combination of histochemical analyses and single-cell RNA-sequencing showed NECAB2 in small- and medium-sized C- and Aδ D-hair low-threshold mechanoreceptors in DRGs, as well as in protein kinase C γ excitatory spinal interneurons. NECAB2 was downregulated by peripheral nerve injury, leading to the hypothesis that NECAB2 loss of function could limit pain sensation. Indeed, Necab2-/- mice reached a pain-free state significantly faster after peripheral inflammation than did WT littermates. Genetic access to transiently activated neurons revealed that a mediodorsal cohort of NECAB2+ neurons mediates inflammatory pain in the mouse spinal dorsal horn. Here, besides dampening excitatory transmission in spinal interneurons, NECAB2 limited pronociceptive brain-derived neurotrophic factor (BDNF) release from sensory afferents. Hoxb8-dependent reinstatement of NECAB2 expression in Necab2-/- mice then demonstrated that spinal and DRG NECAB2 alone could control inflammation-induced sensory hypersensitivity. Overall, we identify NECAB2 as a critical component of pronociceptive pain signaling, whose inactivation offers substantial pain relief.

An innate immune response and altered nuclear receptor activation defines the spinal cord transcriptome during alpha-tocopherol deficiency in Ttpa-null mice

Mice with deficiency in tocopherol (alpha) transfer protein gene develop peripheral tocopherol deficiency and sensory neurodegeneration. Ttpa^-/- mice maintained on diets with deficient α-tocopherol (α-TOH) had proprioceptive deficits by six months of age, axonal degeneration and neuronal chromatolysis within the dorsal column of the spinal cord and its projections into the medulla. Transmission electron microscopy revealed degeneration of dorsal column axons. We addressed the potential pathomechanism of α-TOH deficient neurodegeneration by global transcriptome sequencing within the spinal cord and cerebellum. RNA-sequencing of the spinal cord in Ttpa^-/- mice revealed upregulation of genes associated with the innate immune response, indicating a molecular signature of microglial activation as a result of tocopherol deficiency. For the first time, low level Ttpa expression was identified in the murine spinal cord. Further, the transcription factor liver X receptor (LXR) was strongly activated by α-TOH deficiency, triggering dysregulation of cholesterol biosynthesis. The aberrant activation of transcription factor LXR suppressed the normal induction of the transcription factor retinoic-related orphan receptor-α (RORA), which is required for neural homeostasis. Thus we find that α-TOH deficiency induces LXR, which may lead to a molecular signature of microglial activation and contribute to sensory neurodegeneration.

NECAB3 Promotes Activation of Hypoxia-inducible factor-1 during Normoxia and Enhances Tumourigenicity of Cancer Cells

Unlike most cells, cancer cells activate hypoxia inducible factor-1 (HIF-1) to use glycolysis even at normal oxygen levels, or normoxia. Therefore, HIF-1 is an attractive target in cancer therapy. However, the regulation of HIF-1 during normoxia is not well characterised, although Mint3 was recently found to activate HIF-1 in cancer cells and macrophages by suppressing the HIF-1 inhibitor, factor inhibiting HIF-1 (FIH-1). In this study, we analysed Mint3-binding proteins to investigate the mechanism by which Mint3 regulates HIF-1. Yeast two-hybrid screening using Mint3 as bait identified N-terminal EF-hand calcium binding protein 3 (NECAB3) as a novel factor regulating HIF-1 activity via Mint3. NECAB3 bound to the phosphotyrosine-binding domain of Mint3, formed a ternary complex with Mint3 and FIH-1, and co-localised with Mint3 at the Golgi apparatus. Depletion of NECAB3 decreased the expression of HIF-1 target genes and reduced glycolysis in normoxic cancer cells. NECAB3 mutants that binds Mint3 but lacks an intact monooxygenase domain also inhibited HIF-1 activation. Inhibition of NECAB3 in cancer cells by either expressing shRNAs or generating a dominant negative mutant reduced tumourigenicity. Taken together, the data indicate that NECAB3 is a promising new target for cancer therapy.

iPSC-derived neurons from GBA1-associated Parkinson's disease patients show autophagic defects and impaired calcium homeostasis

Mutations in the acid β-glucocerebrosidase (GBA1) gene, responsible for the lysosomal storage disorder Gaucher's disease (GD), are the strongest genetic risk factor for Parkinson's disease (PD) known to date. Here we generate induced pluripotent stem cells from subjects with GD and PD harbouring GBA1 mutations, and differentiate them into midbrain dopaminergic neurons followed by enrichment using fluorescence-activated cell sorting. Neurons show a reduction in glucocerebrosidase activity and protein levels, increase in glucosylceramide and α-synuclein levels as well as autophagic and lysosomal defects. Quantitative proteomic profiling reveals an increase of the neuronal calcium-binding protein 2 (NECAB2) in diseased neurons. Mutant neurons show a dysregulation of calcium homeostasis and increased vulnerability to stress responses involving elevation of cytosolic calcium. Importantly, correction of the mutations rescues such pathological phenotypes. These findings provide evidence for a link between GBA1 mutations and complex changes in the autophagic/lysosomal system and intracellular calcium homeostasis, which underlie vulnerability to neurodegeneration.

Neuronal calcium-binding proteins 1/2 localize to dorsal root ganglia and excitatory spinal neurons and are regulated by nerve injury

Neuronal calcium (Ca(2+))-binding proteins 1 and 2 (NECAB1/2) are members of the phylogenetically conserved EF-hand Ca(2+)-binding protein superfamily. To date, NECABs have been explored only to a limited extent and, so far, not at all at the spinal level. Here, we describe the distribution, phenotype, and nerve injury-induced regulation of NECAB1/NECAB2 in mouse dorsal root ganglia (DRGs) and spinal cord. In DRGs, NECAB1/2 are expressed in around 70% of mainly small- and medium-sized neurons. Many colocalize with calcitonin gene-related peptide and isolectin B4, and thus represent nociceptors. NECAB1/2 neurons are much more abundant in DRGs than the Ca(2+)-binding proteins (parvalbumin, calbindin, calretinin, and secretagogin) studied to date. In the spinal cord, the NECAB1/2 distribution is mainly complementary. NECAB1 labels interneurons and a plexus of processes in superficial layers of the dorsal horn, commissural neurons in the intermediate area, and motor neurons in the ventral horn. Using CLARITY, a novel, bilaterally connected neuronal system with dendrites that embrace the dorsal columns like palisades is observed. NECAB2 is present in cell bodies and presynaptic boutons across the spinal cord. In the dorsal horn, most NECAB1/2 neurons are glutamatergic. Both NECAB1/2 are transported into dorsal roots and peripheral nerves. Peripheral nerve injury reduces NECAB2, but not NECAB1, expression in DRG neurons. Our study identifies NECAB1/2 as abundant Ca(2+)-binding proteins in pain-related DRG neurons and a variety of spinal systems, providing molecular markers for known and unknown neuron populations of mechanosensory and pain circuits in the spinal cord.

Network state-dependent inhibition of identified hippocampal CA3 axo-axonic cells in vivo

Hippocampal sharp waves are population discharges initiated by an unknown mechanism in pyramidal cell networks of CA3. Axo-axonic cells (AACs) regulate action potential generation through GABAergic synapses on the axon initial segment. We found that CA3 AACs in anesthetized rats and AACs in freely moving rats stopped firing during sharp waves, when pyramidal cells fire most. AACs fired strongly and rhythmically around the peak of theta oscillations, when pyramidal cells fire at low probability. Distinguishing AACs from other parvalbumin-expressing interneurons by their lack of detectable SATB1 transcription factor immunoreactivity, we discovered a somatic GABAergic input originating from the medial septum that preferentially targets AACs. We recorded septo-hippocampal GABAergic cells that were activated during hippocampal sharp waves and projected to CA3. We hypothesize that inhibition of AACs, and the resulting subcellular redistribution of inhibition from the axon initial segment to other pyramidal cell domains, is a necessary condition for the emergence of sharp waves promoting memory consolidation.

Expression of the calcium binding proteins Necab-1,-2 and -3 in the adult mouse hippocampus and dentate gyrus

The family of EF-hand calcium binding proteins is composed of more than 250 members. In search for other neuronal markers, we studied the expression pattern of Necab-1, -2 and -3 in the Ammons horn of adult mice at the gene- and protein levels using in-situ hybridization and immunohistochemistry. The genes for the three Necab's were expressed in specific, non-overlapping areas of the hippocampus. A minority of the Necab-positive interneurons were GABA-ergic, and they virtually never coexpressed one of the classical calcium binding proteins (calretinin, calbindin D-28k and parvalbumin). Necab's are promising new neuronal markers in the brain.

HDAC4 governs a transcriptional program essential for synaptic plasticity and memory

Neuronal activity influences genes involved in circuit development and information processing. However, the molecular basis of this process remains poorly understood. We found that HDAC4, a histone deacetylase that shuttles between the nucleus and cytoplasm, controls a transcriptional program essential for synaptic plasticity and memory. The nuclear import of HDAC4 and its association with chromatin is negatively regulated by NMDA receptors. In the nucleus, HDAC4 represses genes encoding constituents of central synapses, thereby affecting synaptic architecture and strength. Furthermore, we show that a truncated form of HDAC4 encoded by an allele associated with mental retardation is a gain-of-function nuclear repressor that abolishes transcription and synaptic transmission despite the loss of the deacetylase domain. Accordingly, mice carrying a mutant that mimics this allele exhibit deficits in neurotransmission, spatial learning, and memory. These studies elucidate a mechanism of experience-dependent plasticity and define the biological role of HDAC4 in the brain.

Identification of embryonic stem cell-derived midbrain dopaminergic neurons for engraftment

Embryonic stem cells (ESCs) represent a promising source of midbrain dopaminergic (DA) neurons for applications in Parkinson disease. However, ESC-based transplantation paradigms carry a risk of introducing inappropriate or tumorigenic cells. Cell purification before transplantation may alleviate these concerns and enable identification of the specific DA neuron stage most suitable for cell therapy. Here, we used 3 transgenic mouse ESC reporter lines to mark DA neurons at 3 stages of differentiation (early, middle, and late) following induction of differentiation using Hes5::GFP, Nurr1::GFP, and Pitx3::YFP transgenes, respectively. Transplantation of FACS-purified cells from each line resulted in DA neuron engraftment, with the mid-stage and late-stage neuron grafts being composed almost exclusively of midbrain DA neurons. Mid-stage neuron cell grafts had the greatest amount of DA neuron survival and robustly induced recovery of motor deficits in hemiparkinsonian mice. Our data suggest that the Nurr1+ stage (middle stage) of neuronal differentiation is particularly suitable for grafting ESC-derived DA neurons. Moreover, global transcriptome analysis of progeny from each of the ESC reporter lines revealed expression of known midbrain DA neuron genes and also uncovered previously uncharacterized midbrain genes. These data demonstrate remarkable fate specificity of ESC-derived DA neurons and outline a sequential stage-specific ESC reporter line paradigm for in vivo gene discovery.

Adenosine receptors interacting proteins (ARIPs): Behind the biology of adenosine signaling

Adenosine is a well known neuromodulator in the central nervous system. As a consequence, adenosine can be beneficial in certain disorders and adenosine receptors will be potential targets for therapy in a variety of diseases. Adenosine receptors are G protein-coupled receptors, and are also expressed in a large variety of cells and tissues. Using these receptors as a paradigm of G protein-coupled receptors, the present review focus on how protein-protein interactions might contribute to neurotransmitter/neuromodulator regulation, based on the fact that accessory proteins impinge on the receptor/G protein interaction and therefore modulate receptor functioning. Besides affecting receptor signaling, these accessory components also play a key role in receptor trafficking, internalization and desensitization, as it will be reviewed here. In conclusion, the finding of an increasing number of adenosine receptors interacting proteins, and specially the molecular and functional integration of these accessory proteins into receptorsomes, will open new perspectives in the understanding of particular disorders where these receptors have been proved to be involved.

Isolation and expression analysis of Alzheimer's disease-related gene xb51 in zebrafish

XB51 protein is known to interact with the amino-terminal of the X11L protein and to be involved in Abeta40 generation, a hallmark of Alzheimer's disease. In this study, we isolated a zebrafish xb51 homologue and analyzed its spatio-temporal expression pattern during early brain development. The xb51 transcript was first detected in the forebrain at 22 hr post-fertilization. Expression of xb51 in the brain persisted by 36 hpf and became more complex in the brain after 48 hpf. The detailed expression domain of xb51 in the dorsal telencephalon was defined by several molecular markers: emx1, dlx2, lim1, islet1, neurod4/zath3, ngn1, her4, and elavl3/huC. The location of xb51-expressing cells was restricted in a subset of cells positive for elavl3/huC and acetylated alpha-tubulin, markers of differentiating and/or differentiated neurons. Together, these results suggest that xb51 may be required for maturation and maintenance of xb51-expressing neurons in the forebrain.

Mitf functions as an in ovo regulator for cell differentiation and proliferation during development of the chick RPE

Mitf has been reported to play a crucial role in regulating the differentiation of pigment cells in homeothermal animals, i.e. the melanocytes and the retinal pigment epithelium (RPE). However, less is known about the functions of Mitf in the developing RPE. To elucidate such functions, we introduced wild-type and dominant-negative Mitf expression vectors into chick optic vesicles by electroporation. Over-expression of wild-type Mitf altered neural retina cells to become RPE-like and repressed the expression of neural retina markers in vivo. In contrast, dominant-negative Mitf inhibited pigmentation in the RPE. The percentage of BrdU-positive cells decreased during normal RPE development, which was followed by Mitf protein expression. The percentage of BrdU-positive cells decreased in the wild-type Mitf-transfected neural retina, but increased in the dominant-negative Mitf-transfected RPE. p27(kip1), one of the cyclin-dependent kinase inhibitors, begins to be expressed in the proximal region of the RPE at stage 16. Transfection of wild-type Mitf induced expression of p27(kip1), while transfection of dominant-negative Mitf inhibited p27(kip1) expression. We found that Mitf was associated with the endogenous p27(kip1) 5' flanking region. These results demonstrate for the first time "in vivo" that Mitf uniquely regulates both differentiation and cell proliferation in the developing RPE.

The neuronal Ca2+-binding protein 2 (NECAB2) interacts with the adenosine A2A receptor and modulates the cell surface expression and function of the receptor

Heptaspanning membrane also known as G protein-coupled receptors (GPCR) do interact with a variety of intracellular proteins whose function is regulate receptor traffic and/or signaling. Using a yeast two-hybrid screen, NECAB2, a neuronal calcium binding protein, was identified as a binding partner for the adenosine A(2A) receptor (A(2A)R) interacting with its C-terminal domain. Co-localization, co-immunoprecipitation and pull-down experiments showed a close and specific interaction between A(2A)R and NECAB2 in both transfected HEK-293 cells and also in rat striatum. Immunoelectron microscopy detection of NECAB2 and A(2A)R in the rat striatopallidal structures indicated that both proteins are co-distributed in the same glutamatergic nerve terminals. The interaction of NECAB2 with A(2A)R modulated the cell surface expression, the ligand-dependent internalization and the receptor-mediated activation of the MAPK pathway. Overall, these results show that A(2A)R interacts with NECAB2 in striatal neurones co-expressing the two proteins and that the interaction is relevant for A(2A)R function.

EFCBP1/NECAB1, a brain-specifically expressed gene with highest abundance in temporal lobe, encodes a protein containing EF-hand and antibiotic biosynthesis monooxygenase domains

Human EFCBP/NECAB family consists of important participants in neuronal calcium signaling, including EFCBP1/NECAB1, EFCBP2/NECAB2 and EFCBP3/NECAB3. In the present study, we identified the full-length 5229 bp EFCBP1 cDNA which was not described before. Human EFCBP1 encodes a 351 amino acid protein containing two EF-hand motifs and an antibiotic biosynthesis monooxygenase (ABM) domain, sharing 49.9 and 56.8% global homology with human EFCBP2 and EFCBP3. Northern hybridization revealed that EFCBP1 is specifically expressed in brain and its abundance varies in different brain regions. EFCBP1's abundance in temporal lobe, frontal lobe and occipital pole is about 3.4, 1.9 and 1.5 folds of the average abundance in cerebral cortex, respectively. The expression level of EFCBP1 equals in putamen and cerebral cortex, while no hybridization signal was detected in spinal cord. In addition, we found that EFCBP1, EFCBP2 and EFCBP3 share a similar exon distribution mode, though their chromosomal localizations, genomic sizes and intron sizes are diverse.

Somal size of immunolabeled pyramidal cells in the prefrontal cortex of subjects with schizophrenia

BACKGROUND

Although the somal volume of Nissl-stained deep layer 3 pyramidal cells is reduced in prefrontal cortex area 9 of subjects with schizophrenia, the subset of large pyramidal cells immunoreactive (IR) for nonphosphorylated neurofilament protein (NNFP) is not. Consequently, we hypothesized that the somal volume of another subset of pyramidal cells immunoreactive for neuronal calcium binding protein-1 (Necab-1) is significantly reduced in schizophrenia.

METHODS

We labeled Necab-1-IR pyramidal neurons using immunoperoxidase techniques and estimated the mean somal volume in deep layer 3 of area 9 in 13 matched pairs of control and schizophrenic subjects. Identical studies were conducted for pyramidal neurons immunoreactive for neuronal nuclear protein (Neu-N), which is present in all neurons.

RESULTS

In subjects with schizophrenia, neither the mean somal volume of Necab-1-IR pyramidal neurons nor of Neu-N-IR pyramidal neurons was significantly different from control subjects. In addition, the mean somal volume of Neu-N-IR cells was larger than that of Nissl-stained cells in both subject groups, and the magnitude of this difference was greater for the subjects with schizophrenia.

CONCLUSIONS

These findings suggest that immunoperoxidase techniques are associated with an overestimation of the volume of labeled neurons. This confound appears to interact with disease state, and thus obscures differences between diagnostic groups.

The X11/Mint family of adaptor proteins

The X11 protein family are multidomain proteins composed of a conserved PTB domain and two C-terminal PDZ domains. They are involved in formation of multiprotein complexes and two of the family members, X11alpha and X11beta, are expressed primarily in neurones. Not much is known about the principal function of X11s, but through interactions with other neuronal proteins, they are believed to be involved in regulating neuronal signaling, trafficking and plasticity. Furthermore, they have been shown to modulate processing of APP and accumulation of Abeta, making them potential therapeutic targets for Alzheimer's disease. This article reviews the known interactions of the different X11s and their involvement in Alzheimer's disease.

Rab11-FIP4 is predominantly expressed in neural tissues and involved in proliferation as well as in differentiation during zebrafish retinal development

Rab11 family interacting protein 4 (Rab11-FIP4) was initially identified in humans as an Rab11-binding protein, but its biological function has remained unknown. We cloned the zebrafish orthologue of Rab11-FIP4 (zRab11-FIP4) and analyzed its function in vivo by using antisense morpholino. zRab11-FIP4 was expressed as 2 alternative transcripts, i.e., the longer A-form predominantly expressed in neural tissues and the shorter B-form expressed ubiquitously; and in situ hybridization revealed that the A-form was the dominant form. In the developing retina, zRab11-FIP4 was expressed in progenitors throughout the retina at early stages; and then, along with the differentiation, the expression became gradually restricted to the ganglion cell layer and ciliary marginal zone. zRab11-FIP4A knockdown embryos exhibited eye phenotypes similar to those of the shh mutant, such as a small eye with impaired cell proliferation and the delay in cell-cycle exit and differentiation of retinal progenitors. The lack of induction of p57kip2 and enhanced expression of cyclin D1 were observed in the morphant retina. Importantly, the delay in cell-cycle exit was rescued by ectopic expression of either p57Kip2 or dominant-negative PKA, suggesting that Rab11-FIP4A plays pivotal roles in retinal development by regulating Shh signaling and a mechanism acting in parallel with Shh signaling in the control of cell-cycle exit.

Characterization of tescalcin, a novel EF-hand protein with a single Ca2+-binding site: metal-binding properties, localization in tissues and cells, and effect on calcineurin

The tescalcin gene is preferentially expressed during mouse testis differentiation. Here, we demonstrate that this gene encodes a 24 kDa Ca(2+)- and Mg(2+)-binding protein with one consensus EF-hand and three additional domains with EF-hand homology. Equilibrium dialysis with (45)Ca(2+) revealed that recombinant tescalcin binds approximately one Ca(2+) ion at physiological concentrations (pCa 4.5). The intrinsic tryptophan fluorescence of tescalcin was significantly reduced by Ca(2+), indicative of a conformational change. The apparent K(d) for Ca(2+) was 0.8 microM. A point mutation in the consensus EF-hand (D123A) abolished (45)Ca(2+) binding and prevented the fluorescence quenching, demonstrating that the consensus EF-hand alone mediates the Ca(2+)-induced conformational change. Tescalcin also binds Mg(2+) (K(d) 73 microM), resulting in a much smaller fluorescence decrease. In the presence of 1 mM Mg(2+), tescalcin's Ca(2+) affinity is shifted to 3.5 microM. These results illustrate that tescalcin should bind Mg(2+) constitutively in a quiescent cell, replacing it with Ca(2+) during stimulation. We also show that tescalcin is most abundant in adult mouse heart, brain, and stomach, as well as in HeLa and HL-60 cells. Immunofluorescence microscopy revealed that tescalcin is present in the cytoplasm and nucleus, with concentration in membrane ruffles and lamellipodia in the presence of serum, where it colocalizes with the small guanosine triphosphatase Rac-1. Tescalcin shares sequence and functional homology with calcineurin-B homologous protein (CHP), and we found that tescalcin, like CHP, can inhibit the phosphatase activity of calcineurin A. Hence, tescalcin is a novel calcineurin B-like protein that binds a single Ca(2+) ion.

NIP1/XB51/NECAB3 is a potential substrate of Nek2, suggesting specific roles of Nek2 in Golgi

Nek2 is a mammalian protein kinase structurally homologous to Aspergillus NIMA. We previously observed that the Nek2 protein was localized in multiple sites within a cell in a cell cycle stage-specific manner. Such dynamic behavior of Nek2 allowed us to propose that Nek2 may be a mitotic regulator that is involved in diverse cell cycle events. To better understand the cellular processes in which Nek2 participates, we carried out yeast two-hybrid screening and isolated Nek2-Interacting Protein 1 (NIP1), which has been also named as XB51 and NECAB3. Physical interactions of Nek2 with NIP1 were confirmed. In fact, Nek2 can phosphorylate NIP1 in vivo. Immunostaining experiments revealed that NIP1 is a Golgi protein. These results propose a possible involvement of Nek2 in biological processes of the Golgi body, perhaps in relation to the inheritance of Golgi during mitosis or to cell cycle stage-specific regulation of exocytosis.

Presynaptic frequency- and pattern-dependent filtering

Dual intracellular recordings from pairs of synaptically connected neurones have demonstrated that the frequency-dependent pattern of transmitter release varies dramatically between different classes of connections. Somewhat surprisingly, these patterns are not determined by the class of neurone supplying the axon alone, but to a large degree by the class of postsynaptic neurone. A wide range of presynaptic mechanisms, some that depress the release of transmitter and others that enhance release have been identified. It is the selective expression of these different mechanisms that determines the unique frequency- and pattern-dependent properties of each class of connection. Although the molecular interactions underlying these several mechanisms have yet to be fully identified, the wealth and complexity of the protein-protein and protein-lipid interactions that have been shown to control the release of transmitter suggest many ways in which the properties of a synapse may be tuned to respond to particular patterns and frequencies.

XB51 isoforms mediate Alzheimer's beta-amyloid peptide production by X11L (X11-like protein)-dependent and -independent mechanisms

XB51 (derived from X11-like binding protein of clone number 51) was isolated by yeast two-hybrid cDNA screening using the N-terminal domain of X11L (X11-like protein) as a bait. X11L is a neuron-specific adaptor protein that is known to down-regulate APP (beta-amyloid precursor protein) metabolism by associating with the cytoplasmic domain of APP, but the detailed mechanisms are still unknown. Thus the X11L-associated protein XB51 is believed to regulate APP metabolism by modifying X11L function through its interaction with X11L. Here we report that the hXB51 (human XB51 ) gene can yield two transcripts, one with exon 9 spliced out (resulting in the hXB51beta isoform) and the other containing exon 9 (yielding the hXB51alpha isoform). hXB51alpha binds to X11L to form a tripartite complex composed of hXB51alpha, X11L and APP. Complex-formation results in blocking X11L's suppression of Abeta (beta-amyloid) generation from APP. hXB51beta associates with X11L and inhibits its interaction with APP. However, hXB51beta suppresses Abeta generation and secretion in an X11L-independent manner. Thus the hXB51 isoforms regulate Abeta generation differently, either enhancing it by modifying the association of X11L with APP or suppressing it in an X11L-independent manner. These observations advance our understanding of the molecular mechanisms regulating intracellular Abeta production and the pathogenesis of Alzheimer's disease.

Quantitative assessment of transcriptome differences between brain territories

Transcriptome analysis of mammalian brain structures is a potentially powerful approach in addressing the diversity of cerebral functions. Here, we used a microassay for serial analysis of gene expression (SAGE) to generate quantitative mRNA expression profiles of normal adult mouse striatum, nucleus accumbens, and somatosensory cortex. Comparison of these profiles revealed 135 transcripts heterogeneously distributed in the brain. Among them, a majority (78), although matching a registered sequence, are novel regional markers. To improve the anatomical resolution of our analysis, we performed in situ hybridization and observed unique expression patterns in discrete brain regions for a number of candidates. We assessed the distribution of the new markers in peripheral tissues using quantitative RT-PCR, Northern hybridization, and published SAGE data. In most cases, expression was higher in the brain than in peripheral tissues. Because the markers were selected according to their expression level, without reference to prior knowledge, our studies provide an unbiased, comprehensive molecular signature for various mammalian brain structures that can be used to investigate their plasticity under a variety of circumstances.