People - PhD Students
The role of the NMDA receptor in metaplasticity in the visual cortex, and the involvement of metaplasticity in monogenic forms of ASD
The NMDA-receptor is key for excitatory transmission in the brain, particularly during development. NMDA-receptor subunit switching occurs in early development such that the brain turns from being rich in 2B-subunit-containing receptors to containing more 2A. In the visual cortex, the switch is partly visual activity-dependant. Increasing 2A reduces the ability to induce long-term plasticity – a process that strengthens synaptic responses. Therefore, this switch is a form of metaplasticity (plasticity of synaptic plasticity), and is important for preventing hyperactivity. The subunit C-terminal domains are important for subunit trafficking, and we hypothesise that C-terminal-specific events may be required for this metaplasticity. We aim to determine C-terminal involvement by performing dark exposure experiments using rodent models containing either entirely 2A or 2B-C-terminal domains.
Sensory hypersensitivity is seen in autism spectrum disorders (ASDs). Genes encoding the NMDA-receptor 2A and 2B subunits have been implicated in ASDs, and homeostatic plasticity has also been shown to be impaired. Therefore, we hypothesise that that this form of metaplasticity (controlling 2A:2B ratio in the visual cortex) may be impaired in ASDs, contributing to the sensory hypersensitivity phenotype. We aim to test this by performing the above experiments in models of ASDs such as Fragile-X syndrome and Syngap haploinsufficiency.
Understanding how neurodevelopmental disorder-causing missense mutations in EEF1A2 impact on neuronal protein synthesis
De novo mutations in the eukaryotic elongation factor EEF1A2 have been reported in over 100 individuals with epilepsy, intellectual disability and autism. This translation factor is specific for the brain and muscle, and to date over 40 different missense mutations have been recorded in patients, with a range of severity.
Our project aims to investigate the effects of eEF1A2 mutations on protein synthesis, assessing translational fidelity and efficiency and looking for any impact on the neuronal proteome. With so many mutations, an interference in eEF1A2's capacity for protein synthesis seems likely, and there is evidence to suggest that slight perturbations in proteostasis can have severe consequences in long-lived, terminally differentiated neuronal cells.
Indeed, many neurodevelopmental disorders converge at the point of protein synthesis, and there is increasing evidence that aberrant proteostasis is a key underlying cause of neurodegeneration. We aim to elucidate the mechanism by which the eEF1A2 mutations affect development, providing insight into the many disorders underpinned by defects in neuronal protein synthesis.
Visuomotor Processing in Autism Spectrum Disorders: A Decision-Making Perspective
Disrupted sensorimotor processing is a cornerstone characteristic in a range of Autism Spectrum Disorders. However, defects in the neural and computational mechanisms underpinning the decision-making associated with sensorimotor control remain poorly explored and poorly understood. Understanding such cognitive processing requires not only a description of neural activity during cognitive performance but also an understanding of the nature of the processing task itself. Our research project aims to combine widefield cortical imaging with psychophysical modelling of decision-making as a drift diffusion process to generate a mechanistic understanding of sensorimotor decision making during a touchscreen-based visual discrimination reaching task. A central question of this project relates to the recovery of the cognitive processes in rescue studies. For example, it has been established that a reintroduction of the MECP2 protein in rodent models of Rett’s Syndrome rescues the lethal phenotype of the MECP2 knock-out. However, the extend of recovery in the cognitive processes of these mice remains poorly explored. This is an important question with wide implications both in the study of neural circuits as well as for potential therapeutic intervention in patients with neurodevelopmental disorders; can one ever fully recover from such a disorder?
Designing and Testing Molecular Therapies for SynGAP1 Deficiency
In 2009 Hamdan et al. identified novel de novo mutations in SynGAP1 (Synaptic Ras-GTPase Activating Protein1) gene (MIM #603384), with autosomal dominant inheritance, in patients with NSID (Non-Syndromic Intellectual Disability). Lately, SynGAP1 mutations have bene associated also to SID, autism spectrum disorders and epilepsy. An increasing number of patients carrying SynGAP1 mutations have been reported suggesting that it might be a frequent cause of NSID. ID, with 1 to 3% of affected individuals over the total population, is the most frequent disorder diagnosed in children. Patients present consistent limitations in cognitive abilities and adaptive behaviour.
SynGAP1 is a component of the postsynaptic density protein complex and it is involved in AMPAR trafficking regulation and modulation of synaptic plasticity and morphology. We hypothesize that the reestablishment of protein normal levels would avoid the insurgence of intellectual and behavioural abnormalities. My thesis project aims to design and test molecular therapies for SynGAP1-deficiency in rodent models of SynGAP1 deficiency. Specific aims include:
· To investigate expression pattern of SynGAP1 isoforms during development.
· To design and optimize a robust behavioural phenotyping battery.
· To design and generate rational gene therapy cassettes for testing efficacy and safety in rodent models of Syngap1 deficiency.
What drives NMDA receptor dependent metaplasticity and how is it altered in monogenic models of ASD?
Autism spectrum disorder (ASD) is a complex polygenic disorder that can affect up to 1 in 160 children. Mutations in the N-methyl-D-aspartate receptor (NMDAR), one of the major excitatory ion channels in neurons, have been implicated in ASD. NMDARs are highly complex and can be composed of GluN1 and GluN2 subunits (GluN2A-D). In the visual cortex, there is a developmental upregulation of GluN2A but interestingly this can be halted in the juvenile stage, where GluN2B dominates, by sensory deprivation. As sensory deprivation affects electrical activity of neurons, the ratio of GluN2A:GluN2B is thought to be tightly controlled by sensory integration. ASD has been associated with impaired sensory integration, therefore, posing a major challenge for children with ASD. Using novel knock-in mouse models, this project aims to determine how sensory input differentially influences the levels of GluN2A and GluN2B at the synapse in vivo, with particular focus on the their distinctive C-terminal domain sequences and their role in activity-dependent synaptic changes.
Investigating the role of rough-and-tumble play in the development of socio-emotional phenotype in rat models of autism spectrum disorder
Play is a critical and ethologically relevant aspect of the developmental process across phyla and has been particularly well characterised in laboratory rats. Evidence from play deprivation studies strongly suggests that playful interaction during the juvenile period is necessary for normal socio-emotional development and contributes to a stress resilient phenotype in adulthood. Autism spectrum disorder (ASD) is characterised in part by difficulties with reciprocal social interaction and often comorbid with anxiety and depression. Because of its relevance to development in both humans and rats, and the relative ease with which play can be observed in rats in the laboratory, juvenile play is a fruitful behaviour to study in relation to ASD. However, separating the effects of play versus non-playful social behaviour on development is difficult. Most research on play has relied on social isolation to restrict play, although general social interaction and play may contribute differently to development. To address this issue, a novel housing system will be developed to manipulate access to play during specific periods of juvenile development while still allowing direct interaction with peers.
Convergence of spatial representation deficits in autism spectrum disorders
Autism spectrum disorders involve impairments to episodic memory, episodic future thinking, and navigation. The causal mechanisms underlying these deficits, which rely on the ability to generate and maintain representations of space, are unknown. This project will test the hypothesis that deficits in spatial codes in the medial entorhinal cortex (MEC) are a common predictor of phenotypic deficits in ASD models.
Cells in the MEC provide a rich representational repertoire to support complex navigational and spatial processes through the encoding of multiple spatial variables. Lesion or cell type specific manipulations of this region cause spatial memory and navigation impairments. To test whether encoding within the MEC is impaired in ASD models, experiments will employ tetrode recordings of populations of neurons in the MEC of awake, freely moving ASD mice and in mice performing virtual reality-based tasks that specifically probe MEC-dependent path integration.
Developing molecular and genetic therapies for Fragile X Syndrome
Fragile X Syndrome (FXS), is the most common form of inherited intellectual disability and the leading single gene cause of autism. The disorder manifests as a neurodevelopmental disorder, afflicting around 1 in 4000 males and 1 in 8000 females. There is currently no cure. FXS is caused by epigenetic silencing of the X-linked FMR1 gene that encodes the Fragile X Mental Retardation Protein (FMRP). This dynamic protein is involved in multiple processes, primarily through its inhibitory effect on protein translation of target mRNAs by stalling ribosomal subunits.
FXS is a monogenic disorder, making it a potential candidate for a gene therapy approach to treatment. Delivering a functioning copy of the FMR1 gene back to patients could represent a transformative therapy for FXS. We will test this feasibility of this approach by delivering functioning copies of FMR1 to a mouse model of FXS, using a virus delivery system. We will assess if re-expression of FMRP is able to prevent the development of FXS-associated phenotypes in the FXS rodent models, giving us key insights into the possibility of this approach being developed for patients.
Identifying the role of microglia in the developing brain and in plasticity
Microglia are the immune cells of the CNS and play an important role in synaptic maturation and plasticity. During neurodevelopment a large number of synapses are engulfed by microglia and are eliminated in a process termed synaptic pruning. The remaining synapses are strengthened, forming mature neuronal circuits. Studies have shown that disrupted microglial function results in altered synaptic development, and this may contribute to deficits in cognition and behaviour associated with autism spectrum disorders (ASDs). This project will use the newly generated Csf1r∆FIRE/∆FIRE mouse model which selectively lacks brain microglia to investigate the effects of microglia depletion on synaptic development and plasticity. Quantification of structural properties such as synaptic density, dendritic morphology and spine density will be carried out. Synaptic activity will also be measured to investigate the effect of microglia on synaptic plasticity. Lastly changes in behaviour typical of ASD will be assessed.
Circuit deficits associated with SynGAP1 haploinsufficiency
Syngap haploinsufficiency is a relatively common cause of intellectual disability, around 1% of ID cases are caused by this mutation. Most of the patients suffer from epilepsy as well, and in half of the cases it deals with autism spectrum disorders. Patients show delayed development of motor skills, hyperactivity and impairments in social and cognitive abilities.
This disease is caused by an autosomal dominant mutation in the SynGAP1 gene. SynGAP1 is a constituent of the post synaptic density protein complex and contributes to regulate excitatory synapse plasticity. However, how this mutation alters brain connectivity and this eventually leads to ASD/ID remains unknown. To address this issue, we are going to work on a synGAP1-deficiency rat model. We aim to both record and manipulate specific brain regions with in vivo electrophysiology and virus-guided optogenetics, respectively, during social behaviour tasks to detect which are the main impaired circuits under Syngap social impairments.
Investigating the development of functional thalamocortical circuitry in a rat model of Fragile X Syndrome
Fragile X syndrome (FXS) is the most common monogenic cause of autism. It is caused by silencing the Fmr1 gene and it is commonly investigated in rodents with a deletion of this gene (Fmr1-KO), which recapitulate many of the behavioral phenotypes of FXS. Previous experiments have shown synaptic alterations in thalamocortical connections during early development in the Fmr1-KO mouse. The head direction signal is generated in the brainstem and is relayed to the postsubiculum, in the cortex, through the anterodorsal thalamic nucleus (ADN), an example of thalamocortical projections. To examine the functional effects of altered thalamocortical connectivity, this project will investigate the function of the head direction circuitry in young (P8-P14) Fmr1-KO rats. I will use silicon probes to record neuronal activity in the postsubiculum and ADN acutely under anaesthesia and/or during awake experiments, in order to examine the development of direction coding and temporal co-activity relationships in this circuit, in collaboration with researchers at McGill University.