Biology subjects

Gritz, S.

Publications and source records attributed to Gritz, S..

4 recordsLinked to original sources

bioRxiv2026

GIRK Channel Loss of Function Increases Dendritic Excitability in a Mouse Model of GNB1 Encephalopathy

GNB1 encephalopathy (GNB1-E) is a rare neurodevelopmental disorder associated with motor dysfunction, epilepsy and learning disability caused by mutations in the gene encoding the G protein subunit G{beta}1. Previous work has shown that altered G{beta}1 can disrupt activation of G-protein-coupled inwardly rectifying potassium (GIRK) channels, dysregulate neuronal excitability and cause seizures. However, the relevant upstream regulators of G{beta}1 and the consequences of GIRK dysfunction for neuronal synaptic, cellular and circuit function have not been characterized. Here we report that mice of both sexes carrying the deleterious p.I80T mutation in Gnb1 present features consistent with GNB1-E, including developmental delay, decreased locomotion and increased anxiety. Using histology, whole-cell patch-clamp electrophysiology and pharmacology in ex vivo brain slices, we find that hippocampal neurons in heterozygous Gnb1I80T/+ mice exhibit simplified dendritic morphologies, decreased synaptic inhibition mediated by metabotropic GABAB receptors and increased dendritic excitability. These phenotypes result in longer duration dendritic calcium spikes in response to synaptic afferent stimulation, an effect that is reversed by a specific activator of GIRK channels, ML297. Given the known roles of dendritic calcium spikes in driving burst firing and inducing synaptic plasticity, these findings suggest that targeting dendritic excitability has therapeutic potential to address both the seizure susceptibility and learning deficits associated with GNB1-E. Significance StatementGNB1 encephalopathy (GNB1-E) is a rare neurodevelopmental disorder associated with motor dysfunction, epilepsy and learning disability for which there are currently no mechanism-based treatments. Here we show that a pathogenic variant of the G protein subunit G{beta}1 impairs activation of neuronal G-protein-coupled inwardly rectifying potassium (GIRK) channels by inhibitory synaptic GABAB receptors. This leads to increased dendritic excitability and longer duration dendritic calcium spikes in mouse hippocampal neurons in response to stimulation of synaptic inputs. We find that this phenotype is reversed by a drug that activates GIRK channels, opening pathways to develop therapies for GNB1-E that specifically target dendritic excitability.

neuroscience↗

bioRxiv2026

Hippocampal Place Cells with NMDARs Do Not Require Excitation and Inhibition to Be Reciprocally Tuned

In mouse hippocampal area CA1, excitatory pyramidal neurons referred to as "place cells" fire at specific locations in spatial environments during navigation. Many of the excitatory inputs to place cells are themselves spatially tuned, and prior work has shown that synaptic plasticity at those inputs strongly contributes to a selective increase in excitatory synaptic conductance when an animal is inside a cells "place field." It is less clear whether inhibitory inputs to place cells vary with spatial position. Recent studies have investigated whether place cells receive spatially tuned inhibitory conductances by recording place cell activity in vivo and using computational models to help interpret experimental perturbations. One prior study used inhibitory optogenetics to suppress inhibitory neuron firing rates and observed a uniform depolarization of place cells across spatial locations, supporting a model with spatially uniform synaptic inhibition. In apparent conflict, other studies used excitatory optogenetics to depolarize place cells and observed a selective increase in excitability within place fields, supporting a model with a spatially localized decrease in inhibition. However, the latter studies overlooked the contribution of voltage-gated NMDA-type glutamate receptors (NMDARs) to synaptic integration, which are expected to contribute to the balance of excitatory and inhibitory synaptic currents. Here we show that when NMDARs are included at excitatory synapses in simple CA1 place cell models, all experimentally-observed properties of place cells can be recapitulated regardless of whether inhibition increases, decreases, or remains constant inside a place field. Significance StatementThe hippocampus is a brain region required for the formation of new spatial and episodic memories (what happened where and when). Investigating the cellular and circuit mechanisms of memory recall could identify targets for therapies to combat memory decline associated with aging or neurodegeneration. Here we compare the results of computational models of the hippocampus to experimental recordings from mice to better understand the contribution of inhibitory neurons to the expression of spatial memories. We find that a special type of glutamate receptor, the NMDA receptor, helps to maintain the spatial selectivity of excitatory neurons in the hippocampus by counter-balancing fluctuations in the magnitude of inhibitory synaptic currents.

neuroscience↗

bioRxiv2020

A Trypanosoma brucei ORFeome-based Gain-of-Function Library identifies genes that promote survival during melarsoprol treatment

Trypanosoma brucei is an early branching protozoan parasite that causes human and animal African Trypanosomiasis. Forward genetics approaches are powerful tools for uncovering novel aspects of Trypanosomatid biology, pathogenesis, and therapeutic approaches against trypanosomiasis. Here we have generated a T. brucei cloned ORFeome consisting of over 90% of the targeted 7,245 genes and used it to make an inducible Gain-of-Function parasite library broadly applicable to large-scale forward genetic screens. We conducted a proof of principle genetic screen to identify genes whose expression promotes survival in melarsoprol, a critical drug of last resort. The 57 genes identified as overrepresented in melarsoprol survivor populations included the rate-limiting enzyme for the biosynthesis of an established drug target (trypanothione), validating the tool. In addition, novel genes associated with gene expression, flagellum localization, and mitochondrion localization were identified and a subset of those genes increased melarsoprol resistance upon overexpression in culture. These findings offer new insights into Trypanosomatid basic biology, implications for drugs targets, and direct or indirect drug resistance mechanisms. This study generated a T. brucei ORFeome and Gain-of-Function parasite library, demonstrated the libraries usefulness in forward genetic screening, and identified novel aspects of melarsoprol resistance that will be the subject of future investigations. These powerful genetic tools can be used to broadly advance Trypanosomatid research. IMPORTANCETrypanosomatid parasites threaten the health of over 1 billion people worldwide. Because their genomes are highly diverged from well-established eukaryotes, conservation is not always useful in assigning gene functions. However, it is precisely among the Trypanosomatid-specific genes that ideal therapeutic targets might be found. Forward genetics approaches are an effective way to identify novel gene functions. We used an ORFeome approach to clone a large percentage of Trypanosoma brucei genes and generate a Gain-of-Function parasite library. This library was used in a genetic screen to identify genes that promote resistance to the clinically significant, yet highly toxic drug, melarsoprol. Hits arising from the screen demonstrated the librarys usefulness in identifying known pathways and uncovered novel aspects of resistance mediated by proteins localized to the flagellum and mitochondrion. The powerful new genetic tools generated herein are expected to promote advances in Trypanosomatid biology and therapeutic development in the years to come.

genetics↗

bioRxiv2019

A Trypanosoma brucei ORFeome-based Gain-of-Function Library reveals novel genes associated with melarsoprol resistance

Trypanosoma brucei is an early branching protozoan that causes Human and Animal African Trypanosomiasis. Forward genetics approaches are powerful tools for uncovering novel aspects of Trypanosomatid biology, pathogenesis, and therapeutic approaches against trypanosomiasis. Here we have generated a T. brucei ORFeome consisting of over 90% of the targeted genome and used it to make an inducible Gain-of-Function library for broadly applicable forward genetic screening. Using a critical drug of last resort, melarsoprol, we conducted a proof of principle genetic screen. Hits arising from this screen support the significance of trypanothione, a key player in redox metabolism, as a target of melarsoprol and implicate novel proteins of the flagellum and mitochondria in drug resistance. This study has produced two powerful new genetic tools for kinetoplastida research, which are expected to promote major advances in kinetoplastida biology and therapeutic development in the years to come.

genetics↗