NCS-1 protein regulates TRPA1 channel through the PI3K pathway in breast cancer and neuronal cells.

The physical and functional interaction between transient receptor potential channel ankyrin 1 (TRPA1) and neuronal calcium sensor 1 (NCS-1) was assessed. NCS-1 is a calcium (Ca2+) sensor found in many tissues, primarily neurons, and TRPA1 is a Ca2+ channel involved not only in thermal and pain sensation but also in conditions such as cancer and chemotherapy-induced peripheral neuropathy, in which NCS-1 is also a regulatory component.We explored the interactions between these two proteins by employing western blot, qRT-PCR, co-immunoprecipitation, Ca2+ transient monitoring with Fura-2 spectrophotometry, and electrophysiology assays in breast cancer cells (MDA-MB-231) with different levels of NCS-1 expression and neuroblastoma cells (SH-SY5Y).Our findings showed that the expression of TRPA1 was directly correlated with NCS-1 levels at both the protein and mRNA levels. Additionally, we found a physical and functional association between these two proteins. Physically, the NCS-1 and TRPA1 co-immunoprecipitate. Functionally, NCS-1 enhanced TRPA1-dependent Ca2+ influx, current density, open probability, and conductance, where the functional effects depended on PI3K. Conclusion: NCS-1 appears to act not only as a Ca2+ sensor but also modulates TRPA1 protein expression and channel function in a direct fashion through the PI3K pathway. These results contribute to understanding how Ca2+ homeostasis is regulated and provides a mechanism underlying conditions where Ca2+ dynamics are compromised, including breast cancer. With a cellular pathway identified, targeted treatments can be developed for breast cancer and neuropathy, among other related diseases.

Glutamic Acid Modified Gold Nanorod Sensor for the Detection of Calcium ions in Neuronal Cells.

Calcium (Ca2+) ions play a crucial role in the functioning of neurons, governing various aspects of neuronal activity such as rapid modulation and alterations in gene expression. Ca2+ signaling has a significant impact on the development of diseases and the impairment of neuronal functions. Herein, the study reports a Ca2+ ion sensor in neuronal cells using a gold nanorod. The gold nanorod (GA-GNR) conjugated glutamic acid developed in the study was used as a nano-bio probe for the experimental and in vitro detection of calcium. The nanosensor is colloidally stable, preserves plasmonic properties, and shows good viability in neuronal cells, as well as promoting neuron cell line growth. The cytotoxicity and cell penetration of the nanosensor are studied using Raman spectroscopy, brightfield and darkfield microscopy imaging, and MTT assays. The quantification of Ca2+ ions in neuronal cells is determined by monitoring the surface plasmon resonance (SPR) of the GA-GNR. The change in the intensity profile in the presence of Ca2+ incubated neurons was effectively used to develop a portable prototype of an optical Ca2+ sensor, proposing it as a tool for neurodegenerative disease diagnosis and neuromodulation evaluation.

Copines, a Family of Calcium Sensor Proteins and Their Role in Brain Function.

The Copines are a family of evolutionary conserved calcium-binding proteins found in most eukaryotic organisms from protists to humans. They share a unique architecture and contain tandem C2 domains and a Von Willebrand factor type A (VWA) domain. C2 domains in Copines bind calcium, phospholipids, and other proteins and mediate the transient association of these proteins with biological membranes at elevated calcium levels. The VWA domain also binds calcium and is involved in protein-protein interactions. Here, we provide a comprehensive review of the sequences, structures, expression, targeting, and function of the entire family of known Copine proteins (Copine 1-9 in mammals) with a particular emphasis on their functional roles in the mammalian brain. Neuronal Copines are implicated in a wide array of processes from cell differentiation to synaptic transmission and plasticity and are also linked to several pathological conditions from cancers to brain diseases. This review provides the most up-to-date insights into the structure and function of Copines, with an emphasis on their role in brain function.

[Neuronal Calcium Sensor-1: A Zinc/Redox-Dependent Protein of Nervous System Signaling Pathways].

Intracellular calcium signaling is involved in regulating the key functional mechanisms of the nervous system. The control of neuronal excitability and plasticity by calcium ions underlies the mechanisms of higher nervous activity, and the mechanisms of this control are of particular interest to researchers. A family of highly specialized neuronal proteins described in recent decades can translate the information contained in calcium signals into the regulation of channels, enzymes, receptors, and transcription factors. Neuronal calcium sensor-1 (NCS-1) is the most common member of the family, which is intensely expressed in central nervous system (CNS) cells; and controls several vital processes, such as neuronal growth and survival, reception, neurotransmission, and synaptic plasticity. In addition to calcium ions, NCS-1 can bind the so-called mobile, or signaling intracellular zinc, an increased concentration of which is a characteristic feature of cells in oxidative stress. Zinc coordination under these conditions stimulates NCS-1 oxidation to form a disulfide dimer (dNCS-1) with altered functional properties. A combined effect of mobile zinc and an increased redox potential of the medium can thus induce aberrant NCS-1 activity, including signals that promote survival of neuronal cells or induce their apoptosis and, consequently, the development of neurodegenerative processes. The review details the localization, expression regulation, structure, and molecular properties of NCS-1 and considers the current data on its signaling activity in health and disease, including zinc-dependent redox regulation cascades.

Vicia faba SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels.

To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca2+. In our search for species-dependent functional TPC1 channel variants with different luminal Ca2+ sensitivity, we found in total three acidic residues present in Ca2+ sensor sites 2 and 3 of the Ca2+-sensitive AtTPC1 channel from Arabidopsis thaliana that were neutral in its Vicia faba ortholog and also in those of many other Fabaceae. When expressed in the Arabidopsis AtTPC1-loss-of-function background, wild-type VfTPC1 was hypersensitive to vacuole depolarization and only weakly sensitive to blocking luminal Ca2+. When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca2+ sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca2+ sensitivity that together rendered vacuoles hyperexcitable. Thus, natural TPC1 channel variants exist in plant families which may fine-tune vacuole excitability and adapt it to environmental settings of the particular ecological niche.

Copine-6 is a Ca2+ sensor for activity-induced AMPA receptor exocytosis.

The recruitment of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors underlies the strengthening of neuronal connectivity during learning and memory. This process is triggered by N-methyl-D-aspartate (NMDA) receptor-dependent postsynaptic Ca2+ influx. Synaptotagmin (Syt)-1 and -7 have been proposed as Ca2+ sensors for AMPA receptor exocytosis but are functionally redundant. Here, we identify a cytosolic C2 domain-containing Ca2+-binding protein, Copine-6, that forms a complex with AMPA receptors. Loss of Copine-6 expression impairs activity-induced exocytosis of AMPA receptors in primary neurons, which is rescued by wild-type Copine-6 but not Ca2+-binding mutants. In contrast, Copine-6 loss of function does not affect steady-state expression or tetrodotoxin-induced synaptic upscaling of surface AMPA receptors. Loss of Syt-1/Syt-7 significantly reduces Copine-6 protein expression. Interestingly, overexpression of wild-type Copine-6, but not the Ca2+-binding mutants, restores activity-dependent exocytosis of AMPA receptors in Syt-1/Syt-7 double-knockdown neurons. We conclude that Copine-6 is a postsynaptic Ca2+ sensor that mediates AMPA receptor exocytosis during synaptic potentiation.

The Role of NCS1 in Immunotherapy and Prognosis of Human Cancer.

The Neural Calcium Sensor1 (NCS1) is a crucial protein that binds to Ca2+ and is believed to play a role in regulating tumor invasion and cell proliferation. However, the role of NCS1 in immune infiltration and cancer prognosis is still unknown. Our study aimed to explore the expression profile, immune infiltration pattern, prognostic value, biological function, and potential compounds targeting NCS1 using public databases. High expression of NCS1 was detected by immune histochemical staining in LIHC (Liver hepatocellular carcinoma), BRCA (Breast invasive carcinoma), KIRC (Kidney renal clear cell carcinoma), and SKCM (Skin Cutaneous Melanoma). The expression of NCS1 in cancer was determined by TCGA (The Cancer Genome Atlas Program), GTEx (The Genotype-Tissue Expression), the Kaplan-Meier plotter, GEO (Gene Expression Omnibus), GEPIA2.0 (Gene Expression Profiling Interactive Analysis 2.0), HPA (The Human Protein Atlas), UALCAN, TIMER2.0, TISIDB, Metascape, Drugbank, chEMBL, and ICSDB databases. NCS1 has genomic mutations as well as aberrant DNA methylation in multiple cancers compared to normal tissues. Also, NCS1 was significantly different in the immune microenvironment, tumor mutational burden (TMB), microsatellite instability (MSI), and immune infiltrate-associated cells in different cancers, which could be used for the typing of immune and molecular subtypes of cancer and the presence of immune checkpoint resistance in several cancers. Univariate regression analysis, multivariate regression analysis, and gene enrichment analysis to construct prognostic models revealed that NCS1 is involved in immune regulation and can be used as a prognostic biomarker for SKCM, LIHC, BRCA, COAD, and KIRC. These results provide clues from a bioinformatic perspective and highlight the importance of NCS1 in a variety of cancers.

Comparative analysis of wild-type and chloroplast MCU-deficient plants reveals multiple consequences of chloroplast calcium handling under drought stress.

Introduction: Chloroplast calcium homeostasis plays an important role in modulating the response of plants to abiotic and biotic stresses. One of the greatest challenges is to understand how chloroplast calcium-permeable pathways and sensors are regulated in a concerted manner to translate specific information into a calcium signature and to elucidate the downstream effects of specific chloroplast calcium dynamics. One of the six homologs of the mitochondrial calcium uniporter (MCU) was found to be located in chloroplasts in the leaves and to crucially contribute to drought- and oxidative stress-triggered uptake of calcium into this organelle. Methods: In the present study we integrated comparative proteomic analysis with biochemical, genetic, cellular, ionomic and hormone analysis in order to gain an insight into how chloroplast calcium channels are integrated into signaling circuits under watered condition and under drought stress. Results: Altogether, our results indicate for the first time a link between chloroplast calcium channels and hormone levels, showing an enhanced ABA level in the cmcu mutant already in well-watered condition. Furthermore, we show that the lack of cMCU results in an upregulation of the calcium sensor CAS and of enzymes of chlorophyll synthesis, which are also involved in retrograde signaling upon drought stress, in two independent KO lines generated in Col-0 and Col-4 ecotypes. Conclusions: These observations point to chloroplasts as important signaling hubs linked to their calcium dynamics. Our results obtained in the model plant Arabidopsis thaliana are discussed also in light of our limited knowledge regarding organellar calcium signaling in crops and raise the possibility of an involvement of such signaling in response to drought stress also in crops.

The integration of reactive oxygen species (ROS) and calcium signalling in abiotic stress responses.

Reactive oxygen species (ROS) and calcium (Ca2+ ) signalling are interconnected in the perception and transmission of environmental signals that control plant growth, development and defence. The concept that systemically propagating Ca2+ and ROS waves function together with electric signals in directional cell-to-cell systemic signalling and even plant-to-plant communication, is now firmly imbedded in the literature. However, relatively few mechanistic details are available regarding the management of ROS and Ca2+ signals at the molecular level, or how synchronous and independent signalling might be achieved in different cellular compartments. This review discusses the proteins that may serve as nodes or connecting bridges between the different pathways during abiotic stress responses, highlighting the crosstalk between ROS and Ca2+ pathways in cell signalling. We consider putative molecular switches that connect these signalling pathways and the molecular machinery that achieves the synergistic operation of ROS and Ca2+ signals.

A transgenic mouse line for assaying tissue-specific changes in endoplasmic reticulum proteostasis.

Maintenance of calcium homeostasis is important for proper endoplasmic reticulum (ER) function. When cellular stress conditions deplete the high concentration of calcium in the ER, ER-resident proteins are secreted into the extracellular space in a process called exodosis. Monitoring exodosis provides insight into changes in ER homeostasis and proteostasis resulting from cellular stress associated with ER calcium dysregulation. To monitor cell-type specific exodosis in the intact animal, we created a transgenic mouse line with a Gaussia luciferase (GLuc)-based, secreted ER calcium-modulated protein, SERCaMP, preceded by a LoxP-STOP-LoxP (LSL) sequence. The Cre-dependent LSL-SERCaMP mice were crossed with albumin (Alb)-Cre and dopamine transporter (DAT)-Cre mouse lines. GLuc-SERCaMP expression was characterized in mouse organs and extracellular fluids, and the secretion of GLuc-SERCaMP in response to cellular stress was monitored following pharmacological depletion of ER calcium. In LSL-SERCaMP × Alb-Cre mice, robust GLuc activity was observed only in the liver and blood, whereas in LSL-SERCaMP × DAT-Cre mice, GLuc activity was seen in midbrain dopaminergic neurons and tissue samples innervated by dopaminergic projections. After calcium depletion, we saw increased GLuc signal in the plasma and cerebrospinal fluid collected from the Alb-Cre and DAT-Cre crosses, respectively. This mouse model can be used to investigate the secretion of ER-resident proteins from specific cell and tissue types during disease pathogenesis and may aid in the identification of therapeutics and biomarkers of disease.

Synaptotagmin-1 is a Ca2+ sensor for somatodendritic dopamine release.

Modes of somatodendritic transmission range from rapid synaptic signaling to protracted regulation over distance. Somatodendritic dopamine secretion in the midbrain leads to D2 receptor-induced modulation of dopamine neurons on the timescale of seconds. Temporally imprecise release mechanisms are often presumed to be at play, and previous work indeed suggested roles for slow Ca2+ sensors. We here use mouse genetics and whole-cell electrophysiology to establish that the fast Ca2+ sensor synaptotagmin-1 (Syt-1) is important for somatodendritic dopamine release. Syt-1 ablation from dopamine neurons strongly reduces stimulus-evoked D2 receptor-mediated inhibitory postsynaptic currents (D2-IPSCs) in the midbrain. D2-IPSCs evoked by paired stimuli exhibit less depression, and high-frequency trains restore dopamine release. Spontaneous somatodendritic dopamine secretion is independent of Syt-1, supporting that its exocytotic mechanisms differ from evoked release. We conclude that somatodendritic dopamine transmission relies on the fast Ca2+ sensor Syt-1, leading to synchronous release in response to the initial stimulus.

Neuronal Calcium Sensor-1 Protects Cortical Neurons from Hyperexcitation and Ca2+ Overload during Ischemia by Protecting the Population of GABAergic Neurons.

A defection of blood circulation in the brain leads to ischemia, damage, and the death of nerve cells. It is known that individual populations of GABAergic neurons are the least resistant to the damaging factors of ischemia and therefore they die first of all, which leads to impaired inhibition in neuronal networks. To date, the neuroprotective properties of a number of calcium-binding proteins (calbindin, calretinin, and parvalbumin), which are markers of GABAergic neurons, are known. Neuronal calcium sensor-1 (NCS-1) is a signaling protein that is expressed in all types of neurons and is involved in the regulation of neurotransmission. The role of NCS-1 in the protection of neurons and especially their individual populations from ischemia and hyperexcitation has not been practically studied. In this work, using the methods of fluorescence microscopy, vitality tests, immunocytochemistry, and PCR analysis, the molecular mechanisms of the protective action of NCS-1 in ischemia/reoxygenation and hyperammonemia were established. Since NCS-1 is most expressed in GABAergic neurons, the knockdown of this protein with siRNA led to the most pronounced consequences in GABAergic neurons. The knockdown of NCS-1 (NCS-1-KD) suppressed the basic expression of protective proteins without significantly reducing cell viability. However, ischemia-like conditions (oxygen-glucose deprivation, OGD) and subsequent 24-h reoxygenation led to a more massive activation of apoptosis and necrosis in neurons with NCS-1-KD, compared to control cells. The mass death of NCS-1-KD cells during OGD and hyperammonemia has been associated with the induction of a more pronounced network hyperexcitation symptom, especially in the population of GABAergic neurons, leading to a global increase in cytosolic calcium ([Ca2+]i). The symptom of hyperexcitation of neurons with NCS-1-KD correlated with a decrease in the level of expression of the calcium-binding protein-parvalbumin. This was accompanied by an increase in the expression of excitatory ionotropic glutamate receptors, N-methyl-D-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (NMDAR and AMPAR) against the background of suppression of the expression of glutamate decarboxylase (synthesis of γ-aminobutyric acid).

Correlation of fluorescence evolution for quantitative analysis of labels and sensors.

Titration without separation, e.g. quantification of a target species in living cells, is a challenge of analytical chemistry. We perform the selective detection of a target using the kinetics involved in a photochemical process and develop a correlation method that we illustrate by the titration of a fluorescent photoswitcher and the target of a photoswitching sensor. Correlating an input time series and a well-chosen weighting function associated with a variable characteristic time yields a spectrum of characteristic times. The upper integration limit of the correlation output can be chosen to match the argument of an extremum of the spectrum with a characteristic time of the input time series in order to quantify the target. A similar procedure is followed to optimize the signal-to-noise ratio. Selectivity and signal-to-noise ratio associated with 15 weighting functions are theoretically predicted. The results are applied to the titration of the reversibly photoswitchable fluorescent protein Dronpa-2 and the titration of calcium using a reversibly photoswitchable fluorescent sensor. The performance of the correlation method is favorably compared to the one of other dynamic contrast protocols.

Neuronal calcium sensor 2 is key to moulting and oocyte development in the brown planthopper, Nilaparvata lugens.

Intracellular calcium (Ca2+ ) is vital for signal transduction in many cellular events. Several Ca2+ -binding proteins mediate the transduction of intracellular calcium signals. The EF-hand motifs containing neuronal calcium sensor (NCS) proteins are mainly expressed in the nervous system, where they have important roles in the regulation of a variety of neuronal functions. NCS1 has four EF-hand motifs and well-defined neuronal development functions in a variety of eukaryotes. However, NCS2 has only been identified in invertebrates such as insects and nematodes thus far. The functions of NCS2 remain largely unknown. Here, we identified an orthologous NCS2 in the hemipteran Nilaparvata lugens. Based on qRT-PCR, this gene was found to be primarily expressed in the brain. Knockdown of NCS2 in each nymphal instar by RNA interference led to lethality and caused aggradation and disordered arrangement of lipid droplets in the ovaries and testes of adults, which were associated with the absence of mature oocytes in female ovaries and reduction of spermiation in male adults. Our findings revealed a novel function for NCS2 as a regulator in development and reproduction and suggested that this protein had an important role in modulating lipid droplet remodelling in ovary and testis of N. lugens adults.

Nanomolar affinity of EF-hands in neuronal calcium sensor 1 for bivalent cations Pb2+, Mn2+, and Hg2.

Abiogenic metals Pb and Hg are highly toxic since chronic and/or acute exposure often leads to severe neuropathologies. Mn2+ is an essential metal ion but in excess can impair neuronal function. In this study, we address in vitro the interactions between neuronal calcium sensor 1 (NCS1) and divalent cations. Results showed that non-physiological ions (Pb2+ and Mn2+) bind to EF-hands in NCS1 with nanomolar affinity and lower equilibrium dissociation constant than the physiological Ca2+ ion. (Kd, Pb2+ = 7.0 ± 1.0 nM; Kd, Mn2+ = 34.0 ± 6.0 nM; K). Native ultra-high resolution mass spectrometry (FT-ICR MS) and trapped ion mobility spectrometry-mass spectrometry (nESI-TIMS-MS) studies provided the NCS1-metal complex compositions-up to four Ca2+ or Mn2+ ions and three Pb2+ ions (M⋅Pb1-3Ca1-3, M⋅Mn1-4Ca1-2, and M⋅Ca1-4) were observed in complex-and similarity across the mobility profiles suggests that the overall native structure is preserved regardless of the number and type of cations. However, the non-physiological metal ions (Pb2+, Mn2+, and Hg2+) binding to NCS1 leads to more efficient quenching of Trp emission and a decrease in W30 and W103 solvent exposure compared to the apo and Ca2+ bound form, although the secondary structural rearrangement and exposure of hydrophobic sites are analogous to those for Ca2+ bound protein. Only Pb2+ and Hg2+ binding to EF-hands leads to the NCS1 dimerization whereas Mn2+ bound NCS1 remains in the monomeric form, suggesting that other factors in addition to metal ion coordination, are required for protein dimerization.

Polymeric Electrochemical Sensor for Calcium Based on DNA.

Plastic membranes containing deoxyribonucleic acid (DNA) as an electroactive material were acting as Ca2+ selective sensors. Diethyl phthalate (DEP), dioctyl Phthalate (DOP), or nitrophenyl octyl ether (NPOE) were used as plasticizers and polyvinyl chloride (PVC) was the membrane matrix. A sensor with a membrane composition of 120 mg PVC, 60 mg DOP plasticizer, and 2 mg DNA ionophore (DNA: DOP: PVC, 1.0:29.2:0.1 mole) was found to have the best performance. The slope of the calibration graph was 30 mV decade-1. The optimum pH range was 5.7-9.5 for 0.01 M Ca2+. The sensor response time was fast (2-3 s) with a long working period (up to 3 weeks). Excellent selectivity for Ca2+ was indicated by the values of selectivity coefficients for different selected interference. The sensor was used effectively for the estimation of calcium in real samples (fruits, calcium syrup, milk, and dairy products).

Boosting ER-mitochondria calcium transfer to treat Wolfram syndrome.

Wolfram syndrome is a rare genetic disorder characterized by endocrine dysfunction and progressive neurodegeneration. By targeting intracellular calcium dysregulations, a sigma-1 receptor agonist rescued neurological deficits in preclinical models of Wolfram syndrome.

Imaging mitochondrial calcium dynamics in the central nervous system.

Mitochondrial calcium handling is a particularly active research area in the neuroscience field, as it plays key roles in the regulation of several functions of the central nervous system, such as synaptic transmission and plasticity, astrocyte calcium signaling, neuronal activity… In the last few decades, a panel of techniques have been developed to measure mitochondrial calcium dynamics, relying mostly on photonic microscopy, and including synthetic sensors, hybrid sensors and genetically encoded calcium sensors. The goal of this review is to endow the reader with a deep knowledge of the historical and latest tools to monitor mitochondrial calcium events in the brain, as well as a comprehensive overview of the current state of the art in brain mitochondrial calcium signaling. We will discuss the main calcium probes used in the field, their mitochondrial targeting strategies, their key properties and major drawbacks. In addition, we will detail the main roles of mitochondrial calcium handling in neuronal tissues through an extended report of the recent studies using mitochondrial targeted calcium sensors in neuronal and astroglial cells, in vitro and in vivo.

A Dual-Purpose Real-Time Indicator and Transcriptional Integrator for Calcium Detection in Living Cells.

Calcium is a ubiquitous second messenger in eukaryotes, correlated with neuronal activity and T-cell activation among other processes. Real-time calcium indicators such as GCaMP have recently been complemented by newer calcium integrators that convert transient calcium activity into stable gene expression. Here we introduce LuCID, a dual-purpose real-time calcium indicator and transcriptional calcium integrator that combines the benefits of both calcium detection technologies. We show that the calcium-dependent split luciferase component of LuCID provides a real-time bioluminescence readout of calcium dynamics in cells, while the GI/FKF1 split GAL4 component of LuCID converts calcium-generated bioluminescence into stable gene expression. We also show that LuCID's modular design enables it to read out other cellular events such as protein-protein interactions. LuCID adds to the arsenal of tools for studying cells and cell populations that utilize calcium for signaling.

Enhanced detection sensitivity of neuronal activity patterns using CaMPARI1 vs. CaMPARI2.

Calcium-modulated photoactivatable ratiometric integrator (CaMPARI) is a calcium ion (Ca2+)- and light-dependent genetically encoded fluorescent activity integrator that can capture snapshots of neuronal activity through an irreversible process known as photoconversion. This unique property was previously used to label neurons based upon their tuning properties in order to map synaptic connectivity and to record large-scale neuronal activity in freely moving mice without attaching any mechanical device to them. The latest version of CaMPARI (CaMPARI2) was engineered to enhance the contrast generated by photoconverting the green protein to the activity-dependent red form and to reduce the Ca2+-independent photoconversion rate compared to the first generation of CaMPARI (CaMPARI1). However, here we show that this optimization process also resulted in reduced photoconversion efficiency of active neurons in the mouse cortex and hippocampus. Through side-by-side comparison of the two CaMPARI sensors under several experimental conditions, we show that CaMPARI1 exhibits a substantially higher red-to-green ratio in active cells than CaMPARI2. In addition, we show that CaMPARI1 also functions as a more sensitive traditional Ca2+ sensor than CaMPARI2 by producing larger activity-driven dynamic fluorescence changes in the observed neurons. Therefore, we conclude that during the optimization process of CaMPARI2, some of the sensor's characteristics were not predicted properly by in vitro screening assays, and therefore in vivo screening and validation steps should be included in future optimization attempts to increase the predictability of screening pipelines.