Biology subjects

McKenzie, C.

Publications and source records attributed to McKenzie, C..

12 recordsLinked to original sources

bioRxiv2026

Delayed maturation of hippocampal trisynaptic circuitry underlies the protracted development of episodic-like memory

The ability to form high-resolution episodic memories emerges relatively late in development, but the circuit mechanisms underlying this transition are unknown. CA1 receives entorhinal input through a direct monosynaptic pathway and an indirect trisynaptic pathway via the dentate gyrus and CA3. In mice, CA3[->]CA1 innervation matured later than MEC[->]CA1 innervation, with pronounced maturation between P20 and P24. Trisynaptic pathway maturation was necessary for high-resolution memory and was shaped by neuronal activity and early-life experience. Mechanistically, trisynaptic activity promoted perineuronal net assembly around downstream parvalbumin-expressing interneurons, facilitating their maturation and subsequent recruitment during learning to constrain CA1 encoding ensembles. Thus, activity-dependent maturation of trisynaptic circuitry provides a unified circuit and cellular account of a sensitive period for the emergence of episodic-like memory.

neuroscience↗

bioRxiv2026

Latent dentate gyrus engrams formed in infancy scaffold adult learning

Infantile amnesia refers to the loss of event-based memories acquired early in life. In mice, however, these memories are not erased; selective optogenetic stimulation of engrams formed in infancy leads to memory recovery in adulthood, indicating that infant-formed engrams can persist in a latent form. We therefore asked whether these latent engrams, although not accessible through natural retrieval, nonetheless influence related adult learning. Using a contextual fear conditioning paradigm, we find that adult learning is facilitated by prior experience in infancy, both for the same and related contexts. Activity-dependent engram tagging revealed that adult learning reactivates infant-acquired dentate gyrus ensembles, and selective inactivation of these ensembles during adulthood abolished this facilitation. These findings indicate that memories formed in infancy persist as latent engrams that scaffold subsequent learning, consistent with a role in establishing schema-like representations.

neuroscience↗

bioRxiv2026

Distinct CA1 inputs support shifts in neural dimensionality and memory resolution

Event-based memories may be encoded with high (e.g., episodic) or low (e.g., gist) mnemonic resolution. While the CA1 region of the hippocampus encodes events at both scales, it is unclear how such dual coding emerges. Consistent with theoretical predictions1,2, here we show that trisynaptic (from CA3) and monosynaptic (from the medial entorhinal cortex) projections to CA1 encode high- and low-resolution event-based memories, respectively. Recruitment of the trisynaptic pathway during contextual fear conditioning promotes feedforward inhibition of CA1 via activation of parvalbumin-positive (PV+) interneurons. This allows sparse encoding of event-based memories in high-dimensional neural states that support high-resolution contextual fear memories, where mice exhibit conditioned fear only in the training context and not similar contexts. Inhibiting this input during training reduces activation of CA1 PV+ interneurons and feedforward inhibition, shifting neural dynamics to low-dimensional states that support low-resolution contextual fear memories where mice freeze in the training context and similar contexts. These experiments identify a circuit-based mechanism that causally links the dimensionality of CA1 neural dynamics to mnemonic resolution.

neuroscience↗

bioRxiv2025

Dopamine Dynamics in the Nucleus Accumbens Reflect Confidence in Detecting the Occurrence and Non-Occurrence of Visual Signals in Perceptual Decision-Making

Dopamine (DA) is critically involved in processes such as reward anticipation, attention, and decision - making. The present study examined the temporal dynamics of phasic DA transients in the nucleus accumbens core (NAcC) during a visual decisional task based on signal detection theory, using the fluorescent DA sensor dLight1.3b. During the decision-making phase, DA transients in the NAcC encoded real-time outcome expectancy, apparently reflecting the confidence of rats in their choices. Reward prediction errors (RPEs) emerged following reward delivery and omission and were amplified under conditions of increased uncertainty, produced either by degrading the visual target or introducing interfering distraction. Moreover, DA transients were elicited on both visual signal and no-signal trials. These findings demonstrate that DA fluctuations in the NAcC reflect the RPE that incorporates confidence and levels of uncertainty, emphasizing an involvement of nucleus accumbens DA in adaptive decision-making.

neuroscience↗

bioRxiv2024

Different fluorescent labels report distinct components of spHCN channel voltage sensor movement

Voltage clamp fluorometry was used to probe the S4 helix movement in the voltage sensing domain of the sea urchin HCN channel expressed in Xenopus oocytes. Markedly different fluorescence responses were obtained with either ALEXA-488 or MTS-TAMRA covalently linked to Cys332 at the N-terminal end of S4. With hyperpolarizing steps, ALEXA-488 fluorescence increased rapidly showing characteristics consistent with it reporting the initial inward movement of S4 in agreement with previous studies. In contrast, MTS-TAMRA fluorescence was slower and correlated with the early phase of channel opening. In addition, a slow fluorescence component was resolved with both labels that tracked the development of the mode shift or channel hysteresis. This was quantitated as an increased deactivation tail current delay with concomitantly longer activation periods and was found to depend strongly on the presence of K+ ions in the pore. This indicated that the microenvironment of the fluorescent probes attached to Cys332 was strongly influenced by conformational changes in the pore domain. Collisional quenching experiments established that ALEXA-488 was more exposed to solvent than MTS-TAMRA. This was supported by structural predictions based on homology modelling of spHCN in the closed and open conformations with covalently linked fluorophores. This study demonstrates that components of S4 movement during channel activation can be kinetically resolved using different fluorescent probes to reveal three distinct biophysical properties: voltage-sensor movement, early channel opening and mode-shift. These data support the use of different labelling probes to interrogate distinct biophysical aspects of voltage-gated membrane proteins. SummaryVoltage clamp fluorometry was used to probe the S4 helix movement in the voltage sensing domain of the spHCN channel expressed in Xenopus oocytes, labeled with either ALEXA-488 or MTS-TAMRA. Each fluorophore reported different components of S4 movement.

biophysics↗

bioRxiv2023

A Protein Blueprint of the Diatom CO2-Fixing Organelle

Diatoms are central to the global carbon cycle. At the heart of diatom carbon fixation is an overlooked organelle called the pyrenoid, where concentrated CO2 is delivered to densely packed Rubisco. Diatom pyrenoids fix approximately one-fifth of global CO2, but virtually nothing is known about this organelle in diatoms. Using large-scale fluorescence protein tagging and affinity purification-mass spectrometry, we generate a high-confidence spatially-defined protein-protein interaction network for the diatom pyrenoid. Within our pyrenoid interaction network are 10 proteins with no known function. We show that six of these form a static shell encapsulating the Rubisco matrix of the pyrenoid, with the shell critical for pyrenoid structural integrity, shape, and function. Although not conserved at a sequence level, the diatom pyrenoid shares some architectural similarities to prokaryotic carboxysomes. Collectively, our results support the convergent evolution of pyrenoids across the two main plastid lineages and uncover a major structural and functional component of global CO2 fixation.

cell biology↗

bioRxiv2023

Exploration of T-cell immune responses by expression of a dominant-negative SHP1 and SHP2

SHP1 and SHP2 are SH2 domain-containing proteins which have inhibitory phosphatase activity when recruited to phosphorylated ITIMs and ITSMs on inhibitory immune receptors. Consequently, SHP1 and SHP2 are key proteins in the transmission of inhibitory signals within T cells, constituting an important point of convergence for diverse inhibitory receptors. Therefore, SHP1 and SHP2 inhibition may represent a strategy for preventing immunosuppression of T cells mediated by cancers hence improving immunotherapies directed against these malignancies. Both SHP1 and SHP2 contain dual SH2 domains responsible for localization to the endodomain of inhibitory receptors and a protein tyrosine phosphatase domain which dephosphorylates and thus inhibits key mediators of T cell activation. We explored the interaction of the isolated SH2 domains of SHP1 and SHP2 to inhibitory motifs from PD1 and identified strong binding of both SH2 domains from SHP2 and more moderate binding in the case of SHP1. We next explored whether these a truncated form of SHP1/2 comprising only of SH2 domains (dSHP1/2) could act in a dominant negative fashion by preventing docking of the wild type proteins. When co-expressed with CARs we found that dSHP2 but not dSHP1 could alleviate immunosuppression mediated by PD1. We next explored the capacity of dSHP2 to bind with other inhibitory receptors and observed several potential interactions. In vivo we observed that the expression of PDL1 on tumor cells impaired the ability of CAR T cells to mediate tumor rejection and this effect was partially reversed by the co-expression of dSHP2 albeit at the cost of reduced CAR T cell proliferation. Modulation of SHP1 and SHP2 activity in engineered T cells through the expression of these truncated variants may enhance T cell activity and hence efficacy in the context of cancer immunotherapy.

immunology↗

bioRxiv2023

Novel Fas-TNFR chimeras that prevents Fas ligand-mediated kill and signals synergistically to enhance CAR T-cell efficacy

The hostile tumour microenvironment limits the efficacy of adoptive cell therapies. Activation of the Fas death receptor initiates apoptosis and disrupting these receptors could be key to increase CAR T-cell efficacy. We screened a library of Fas-TNFR proteins identifying several novel chimeras that not only prevented Fas ligand-mediated kill, but also enhanced CAR T-cell efficacy by signalling synergistically with the CAR. Upon binding Fas ligand, Fas-CD40 activated the NF-{kappa}B pathway, inducing greatest proliferation and IFN{gamma} release out of all Fas-TNFRs tested. Fas-CD40 induced profound transcriptional modifications, particularly genes relating to the cell cycle, metabolism, and chemokine signalling. Co-expression of Fas-CD40 with either 4-1BB- or CD28-containing CARs increased in vitro efficacy by eliciting maximal CAR T-cell proliferation and cancer target cytotoxicity, and enhanced tumour killing and overall mouse survival in vivo. Functional activity of the Fas-TNFRs were dependent on the co-stimulatory domain within the CAR, highlighting crosstalk between signalling pathways. Furthermore, we show that a major source for Fas-TNFR activation derives from CAR T cells themselves via activation-induced Fas ligand upregulation, highlighting a universal role of Fas-TNFRs in augmenting CAR T-cell responses. We have identified Fas-CD40 as the optimal chimera for overcoming Fas ligand-mediated kill and enhancing CAR T-cell efficacy.

synthetic biology↗

bioRxiv2023

A shift in the mechanisms controlling hippocampal engram formation during brain maturation

The ability to form precise, episodic memories develops with age, with young children only able to form gist-like memories that lack precision. The cellular and molecular events in the developing hippocampus that underlie the emergence of precise, episodic-like memory formation are unclear. In mice, the absence of a competitive neuronal engram allocation process in the immature hippocampus precluded the formation of sparse engrams and precise memories until the fourth postnatal week, when inhibitory circuits in the hippocampus mature. This age-dependent shift in precision of episodic-like memories involved the functional maturation of parvalbumin-expressing interneurons in subfield CA1 by extracellular perineuronal nets which is necessary and sufficient for the onset of competitive neuronal allocation, sparse engram formation, and memory precision. One-Sentence SummaryEpisodic-like memory precision requires maturation of hippocampal inhibitory interneurons by the extracellular matrix.

neuroscience↗

bioRxiv2022

The development of compulsive coping behaviors depends on the engagement of dorsolateral striatum dopamine-dependent mechanisms

Humans greatly differ in how they cope with stress, a natural behavior learnt through negative reinforcement. Some individuals engage in displacement activities, others in exercise or comfort eating, and others still in alcohol use. Across species, adjunctive behaviors, such as polydipsic drinking, are used as a form of displacement activity that reduces distress. Some individuals, in particular those that use alcohol to self-medicate, tend to lose control over such coping behaviors, which become excessive and compulsive. However, the psychological and neural mechanisms underlying this individual vulnerability have not been elucidated. Here we tested the hypothesis that the development of compulsive adjunctive behaviors stems from the functional engagement of the dorsolateral striatum (DLS) dopamine-dependent habit system after a prolonged history of adjunctive responding. We measured in longitudinal studies in male Sprague Dawley rats the sensitivity of early established vs compulsive polydipsic water or alcohol drinking to a bilateral infusion of the dopamine receptor antagonist -flupentixol into the anterior DLS (aDLS). While most rats acquired a polydipsic drinking response with water, others only did so with alcohol. Whether reliant on water or alcohol, the acquisition of this coping response was insensitive to aDLS dopamine receptor blockade. In contrast, after prolonged experience, adjunctive drinking became dependent on the aDLS dopamine-dependent habit system at a time it was compulsive in vulnerable individuals. These data suggest that habits may develop out of negative reinforcement and that the engagement of their underlying striatal system is necessary for the manifestation of adjunctive behaviors. Significance statementHarnessing the individual variability that rodents, like humans, show to engage in adaptive or maladaptive coping strategies, which can result in the development of compulsive disorders, here we demonstrate that the functional engagement of the dorsolateral striatum-dependent habit system precipitates the transition to compulsion in rats that have acquired a polydipsic adjunctive drinking response with water or alcohol as a means to cope with distress. The results of this study not only provide evidence for the emergence of instrumental habits under negative reinforcement, but they also reveal that compulsive behaviors that originate from the loss of control over coping strategies are mediated by the dorsolateral striatum-dependent habit system.

neuroscience↗

bioRxiv2021

Opposing roles of the dorsolateral and dorsomedial striatum in the acquisition of skilled action sequencing

The shift in control from dorsomedial to dorsolateral striatum during skill and habit formation has been well established, but whether striatal subregions orchestrate this shift co-operatively or competitively remains unclear. Cortical inputs have also been implicated in the shift towards automaticity, but it is unknown if they mirror their downstream striatal targets across this transition. We addressed these questions using a five-step heterogeneous action sequencing task in rats that is optimally performed by automated chains of actions. By optimising automatic habitual responding, we discovered that loss of function in the dorsomedial striatum accelerated sequence acquisition. In contrast, loss of function in the dorsolateral striatum impeded acquisition of sequencing, demonstrating functional opposition within the striatum. Unexpectedly the medial prefrontal cortex was not involved, however the lateral orbitofrontal cortex was critical. These results shift current theories about striatal control of behavior to a model of competitive opposition, where the dorsomedial striatum acts in a gating role to inhibit dorsolateral-striatum driven behavior.

neuroscience↗

bioRxiv2020

Three LysM effectors of Zymoseptoria tritici collectively disarm chitin-triggered plant immunity

SUMMARYChitin is a major structural component of fungal cell walls and acts as a microbe-associated molecular pattern (MAMP) that, upon recognition by a plant host, triggers the activation of immune responses. In order to avoid the activation of these responses, the Septoria tritici blotch (STB) pathogen of wheat, Zymoseptoria tritici, secretes LysM effector proteins. Previously, the LysM effectors Mg1LysM and Mg3LysM were shown to protect fungal hyphae against host chitinases. Furthermore, Mg3LysM, but not Mg1LysM, was shown to suppress chitin-induced reactive oxygen species (ROS) production. Whereas initially a third LysM effector gene was disregarded as a presumed pseudogene, we now provide functional data to show that also this gene encodes a LysM effector, named Mgx1LysM, that is functional during wheat colonization. While Mg3LysM confers a major contribution to Z. tritici virulence, Mgx1LysM and Mg1LysM contribute to Z. tritici virulence with smaller effects. All three LysM effectors display partial functional redundancy. We furthermore demonstrate that Mgx1LysM binds chitin, suppresses the chitin-induced ROS burst and is able to protect fungal hyphae against chitinase hydrolysis. Finally, we demonstrate that Mgx1LysM is able to undergo chitin-induced polymerisation. Collectively, our data show that Zymoseptoria tritici utilizes three LysM effectors to disarm chitin-triggered wheat immunity.Competing Interest StatementThe authors have declared no competing interest.View Full Text

plant biology↗