Summary HSP90 acts as a protein-folding buffer that shapes the manifestations of genetic variation in model organisms. Whether HSP90 influences the consequences of mutations in humans, potentially modifying the clinical course of genetic diseases, remains unknown. Mining data for >1,500 disease-causing mutants, we found strong correlation between reduced phenotypic severity and a dominant (HSP90≥HSP70) increase in mutant engagement by HSP90. Examining the cancer predisposition syndrome Fanconi Anemia in depth revealed that mutant FANCA proteins engaged predominantly by HSP70 had severely compromised function. In contrast, the function of less severe mutants was preserved by a dominant increase in HSP90 binding. Reducing HSP90’s buffering capacity with inhibitors or febrile temperatures destabilized HSP90-buffered mutants, exacerbating FA-related chemosensitivities. Strikingly, a compensatory FANCA somatic mutation from an “experiment of nature” in monozygotic twins both prevented anemia and reduced HSP90 binding. These findings provide one plausible mechanism for the variable expressivity and environmental sensitivity of genetic diseases.

Background Fetal alcohol syndrome (FAS) due to gestational alcohol exposure represents one of the most common causes of nonheritable lifelong disability worldwide. In vitro and in vivo models have successfully recapitulated multiple facets of the disorder, including morphological and behavioral deficits, but far less is understood regarding the molecular and genetic mechanisms underlying FAS. Methods In this study, we utilized an in vitro human pluripotent stem cell‐based (hPSC) model of corticogenesis to probe the effects of early, chronic intermittent alcohol exposure on the transcriptome of first trimester‐equivalent cortical neurons. Results We used RNA sequencing of developing hPSC‐derived neurons treated for 50 days with 50 mM ethanol and identified a relatively small number of biological pathways significantly altered by alcohol exposure. These included cell‐type specification, axon guidance, synaptic function, and regional patterning, with a notable upregulation of WNT signaling‐associated transcripts observed in alcohol‐exposed cultures relative to alcohol‐naïve controls. Importantly, this effect paralleled a shift in gene expression of transcripts associated with regional patterning, such that caudal forebrain‐related transcripts were upregulated at the expense of more anterior ones. Results from H9 embryonic stem cells were largely replicated in an induced pluripotent stem cell line (IMR90‐4), indicating that these patterning alterations are not cell line‐specific. Conclusions We found that a major effect of chronic intermittent alcohol on the developing cerebral cortex is an overall imbalance in regionalization, with enrichment of gene expression related to the production of posterodorsal progenitors and a diminution of anteroventral progenitors. This finding parallels behavioral and morphological phenotypes observed in animal models of high‐dose prenatal alcohol exposure, as well as patients with FAS.

Optogenetics is a widely used tool for studying neural circuits. However, non-invasive methods for light delivery in the brain are needed to avoid physical damage typically caused by intracranial insertion of light guides. An innovative strategy could employ X-ray activation of radioluminescent particles (RLPs) to emit localized light. We previously reported that RLPs composed of cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light, are biocompatible with neuronal function and synaptic transmission. However, little is known about the consequences of acute X-ray exposure on synaptic function and long-term plasticity. Furthermore, modulation of neuronal or synaptic function by X-ray induced radioluminescence from RLPs has not yet been demonstrated. Here we show that 30 minutes of X-ray exposure at a rate of 0.042 Gy/second caused no change in the strength of basal glutamatergic transmission during extracellular dendritic field recordings in mouse hippocampal slices. Additionally, long-term potentiation (LTP), a robust measure of synaptic integrity, was able to be induced after X-ray exposure and expressed at a magnitude not different from control conditions (absence of X-rays). This is important as synaptic plasticity is critical to learning and memory. Next, we used molecular and electrophysiological approaches to determine if X-ray dependent radioluminescence emitted from RLPs can activate light sensitive proteins. We found that X-ray stimulation of RLPs elevated cAMP levels in HEK293T cells expressing OptoXR, a chimeric opsin receptor that combines the extracellular lightsensitive domain of channelrhodopsin-2 (ChR2) with an intracellular second messenger signaling cascade. This demonstrates that X-ray radioluminescence from LSO:Ce particles can activate OptoXR. Next, we tested whether X-ray activation of the RLPs can enhance synaptic activity in whole-cell recordings from hippocampal neurons expressing ChR2, both in cell culture and acute hippocampal slices. Importantly, Xray radioluminescence caused an increase in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) in both systems, indicating activation of ChR2 and excitation of neurons. Together, our results show that X-ray activation of LSO:Ce particles can heighten cellular and synaptic function. The combination of LSO:Ce inorganic scintillators and X-rays is therefore a viable method for optogenetics as an alternative to more invasive light delivery methods.

Nanoparticle-based delivery systems have become a popular method for targeting tumors and impermeable tissue with drugs for treatment and imaging markers for biodetection. Nanomaterials are beneficial for medical treatment because they can be modified to have increased stability and carrying capacity, and their size and surface modifications allow them to reach otherwise impenetrable tissue. Nanoparticles have become particularly popular in medical imaging since they can be produced as scintillators that emit visible light which can be used in PET detectors, or they could be made with paramagnetic materials for magnetic resonance imaging. Localized or systemic injection can be used for delivery of nanoparticles; however, systemic injection without appropriate surface modifications is subjected to uptake by the mononuclear phagocytic system which clears particles from the circulation rapidly limiting their accumulation at target tissue and reducing efficacy. Here we demonstrate the biodistribution of Yttrium oxyorthosilicate nanoparticles doped with Cerium after localized injection to the cerebral cortex.

Ethanol (EtOH) exposure in early development can lead to profound consequences on neural progenitor cells (NPC) and the neurons that they generate. The clusters of neurological and anatomical hallmarks associated with prenatal EtOH exposure are collectively referred to as fetal alcohol spectrum (FAS). Because EtOH affects multiple developmental processes depending on dosage, frequency and timing of exposure, FAS symptoms exists on a spectrum from relatively benign to severely debilitating intellectual disability, including difficulties with learning, memory and executive function. While animal models successfully recapitulate multiple aspects of FAS including characteristically altered craniofacial morphogenesis and behavioral deficits, much less is understood regarding how EtOH exposure affects human NPCs and neuronal development. In this study, we utilize an in vitro human pluripotent stem cell-based (hPSC) model of early neurogenesis to probe the differences in the development of NPCs and post-mitotic neurons using bulk RNA sequencing. Our findings include specific alterations in the areas of WNT signaling, cortical regionalization and synapse formation.