Targeting neuronal and glial cell types with synthetic promoter AAVs in mice, non-human primates and humans

Targeting genes to specific neuronal or glial cell types is valuable for both understanding and repairing brain circuits. Adeno-associated viruses (AAVs) are frequently used for gene delivery, but targeting expression to specific cell types is an unsolved problem. We created a library of 230 AAVs, each with a different synthetic promoter designed using four independent strategies. We show that a number of these AAVs specifically target expression to neuronal and glial cell types in the mouse and non-human primate retina in vivo and in the human retina in vitro. We demonstrate applications for recording and stimulation, as well as the intersectional and combinatorial labeling of cell types. These resources and approaches allow economic, fast and efficient cell-type targeting in a variety of species, both for fundamental science and for gene therapy.

How Diverse Retinal Functions Arise from Feedback at the First Visual Synapse

Many brain regions contain local interneurons of distinct types. How does an interneuron type contribute to the input-output transformations of a given brain region? We addressed this question in the mouse retina by chemogenetically perturbing horizontal cells, an interneuron type providing feedback at the first visual synapse, while monitoring the light-driven spiking activity in thousands of ganglion cells, the retinal output neurons. We uncovered six reversible perturbation-induced effects in the response dynamics and response range of ganglion cells. The effects were enhancing or suppressive, occurred in different response epochs, and depended on the ganglion cell type. A computational model of the retinal circuitry reproduced all perturbation-induced effects and led us to assign specific functions to horizontal cells with respect to different ganglion cell types. Our combined experimental and theoretical work reveals how a single interneuron type can differentially shape the dynamical properties of distinct output channels of a brain region.

Cis-regulatory landscapes of four cell types of the retina

The retina is composed of ∼50 cell-types with specific functions for the process of vision. Identification of the cis-regulatory elements active in retinal cell-types is key to elucidate the networks controlling this diversity. Here, we combined transcriptome and epigenome profiling to map the regulatory landscape of four cell-types isolated from mouse retinas including rod and cone photoreceptors as well as rare inter-neuron populations such as horizontal and starburst amacrine cells. Integration of this information reveals sequence determinants and candidate transcription factors for controlling cellular specialization. Additionally, we refined parallel reporter assays to enable studying the transcriptional activity of large collection of sequences in individual cell-types isolated from a tissue. We provide proof of concept for this approach and its scalability by characterizing the transcriptional capacity of several hundred putative regulatory sequences within individual retinal cell-types. This generates a catalogue of cis-regulatory regions active in retinal cell types and we further demonstrate their utility as potential resource for cellular tagging and manipulation.

Congenital Nystagmus Gene FRMD7 Is Necessary for Establishing a Neuronal Circuit Asymmetry for Direction Selectivity

Neuronal circuit asymmetries are important components of brain circuits, but the molecular pathways leading to their establishment remain unknown. Here we found that the mutation of FRMD7, a gene that is defective in human congenital nystagmus, leads to the selective loss of the horizontal optokinetic reflex in mice, as it does in humans. This is accompanied by the selective loss of horizontal direction selectivity in retinal ganglion cells and the transition from asymmetric to symmetric inhibitory input to horizontal direction-selective ganglion cells. In wild-type retinas, we found FRMD7 specifically expressed in starburst amacrine cells, the interneuron type that provides asymmetric inhibition to direction-selective retinal ganglion cells. This work identifies FRMD7 as a key regulator in establishing a neuronal circuit asymmetry, and it suggests the involvement of a specific inhibitory neuron type in the pathophysiology of a neurological disease.

Video Abstract

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FRMD7 is required for the horizontal optokinetic reflex in mice as in humans

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Horizontal direction selectivity is lost in the retina of FRMD7 mutant mice

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Asymmetry of inhibitory inputs to horizontal DS cells is lost in FRMD7 mutant mice

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FRMD7 is expressed in ChAT-expressing cells in the retina of mice and primates

Rods in daylight act as relay cells for cone-driven horizontal cell-mediated surround inhibition

Vertebrate vision relies on two types of photoreceptors, rods and cones, which signal increments in light intensity with graded hyperpolarizations. Rods operate in the lower range of light intensities while cones operate at brighter intensities. The receptive fields of both photoreceptors exhibit antagonistic center-surround organization. Here we show that at bright light levels, mouse rods act as relay cells for cone-driven horizontal cell-mediated surround inhibition. In response to large, bright stimuli that activate their surrounds, rods depolarize. Rod depolarization increases with stimulus size, and its action spectrum matches that of cones. Rod responses at high light levels are abolished in mice with nonfunctional cones and when horizontal cells are reversibly inactivated. Rod depolarization is conveyed to the inner retina via postsynaptic circuit elements, namely the rod bipolar cells. Our results show that the retinal circuitry repurposes rods, when they are not directly sensing light, to relay cone-driven surround inhibition.

miRNAs 182 and 183 are necessary to maintain adult cone photoreceptor outer segments and visual function

The outer segments of cones serve as light detectors for daylight color vision, and their dysfunction leads to human blindness conditions. We show that the cone-specific disruption of DGCR8 in adult mice led to the loss of miRNAs and the loss of outer segments, resulting in photoreceptors with significantly reduced light responses. However, the number of cones remained unchanged. The loss of the outer segments occurred gradually over 1 month, and during this time the genetic signature of cones decreased. Reexpression of the sensory-cell-specific miR-182 and miR-183 prevented outer segment loss. These miRNAs were also necessary and sufficient for the formation of inner segments, connecting cilia and short outer segments, as well as light responses in stem-cell-derived retinal cultures. Our results show that miR-182- and miR-183-regulated pathways are necessary for cone outer segment maintenance in vivo and functional outer segment formation in vitro.

The first stage of cardinal direction selectivity is localized to the dendrites of retinal ganglion cells

Inferring the direction of image motion is a fundamental component of visual computation and essential for visually guided behavior. In the retina, the direction of image motion is computed in four cardinal directions, but it is not known at which circuit location along the flow of visual information the cardinal direction selectivity first appears. We recorded the concerted activity of the neuronal circuit elements of single direction-selective (DS) retinal ganglion cells at subcellular resolution by combining GCaMP3-functionalized transsynaptic viral tracing and two-photon imaging. While the visually evoked activity of the dendritic segments of the DS cells were direction selective, direction-selective activity was absent in the axon terminals of bipolar cells. Furthermore, the glutamate input to DS cells, recorded using a genetically encoded glutamate sensor, also lacked direction selectivity. Therefore, the first stage in which extraction of a cardinal motion direction occurs is the dendrites of DS cells.

The Doppler-guided transfalcine venous approach in selected cases of vein of Galen malformations

OBJECTIVE

This investigation was performed to evaluate the specific procedural issues and indications of a surgically assisted Doppler-guided endovascular transfalcine venous approach for the treatment of vein of Galen aneurysmal malformations (VGAM) in critically ill neonates.

PATIENTS AND METHODS

Two neonates out of a clinical series of 15 children (8 males and 7 females) with vein of Galen malformations were treated by our neurovascular team, using a combined surgically assisted endovascular transfalcine approach. In the biplanar angiography room a radiographically guided craniotomy (1.5 cm) was placed over the cranial projection of the falciforme sinus. After craniotomy the orthograd flow of the falciforme sinus was identified by Doppler ultrasonography. The sinus was punctured by an i. v. cannula with injection port and was sutured to the skin. A microcatheter was maneuvered over a guide into the malformation under fluoroscopic control. For embolization Guglielmi electrolytically detachable platinum coils were placed into the malformation as an embolic agent. Neurological examination records, available MR images, computed tomographic scans, pre- and postembolization angiograms and follow-up data were analyzed.

RESULTS

In both individuals the malformation was classified as VGAM. The follow-up was 6 and 7 months, respectively. No technique associated morbidity or mortality occurred in the present series. At discharge both selected neonates were in stable condition and the flow in the VGAMs could be significantly reduced by a combination of approaches including the venous transfalcine approach. Meanwhile, 6 months after birth one neonate died due to a deterioration of the pulmonary hypertension.

CONCLUSIONS

Endovascular treatment is presently the most efficient strategy to allow neonates and infants survive the early manifestation of vein of Galen malformations and probably render a normal neurological development. Consequently, a combination of approaches in selected cases including the Doppler guided venous transfalcine route should be regarded as a preferential treatment modality, especially in patients with arterial vasospasms and venous stenosis.

[High dose chemotherapy with thiotepa, carboplatin, VP16 and autologous stem cell transplantation in treatment of malignant brain tumors with poor prognosis. Results of a mono-center pilot study]

More than half of the children and adolescents with malignant brain tumors will relapse following initial therapy. Irrespective of the therapeutic modalities the prognosis of patients with recurrent or metastatic brain tumors is still poor. New strategies such as high dose chemotherapy (HDCT) with autologous blood stem cell transplantation (ABSCT) offer the possibility to improve the longterm prognosis of these patients. Following conventional chemotherapy with carboplatin/etoposide and after achieving complete or partial remission (CR or PR) 10 patients aged from 3.2 to 25.5 years (median, 10.3 years) with refractory or recurrent malignant brain tumors (anaplastic astrocytoma/glioblastoma, n = 2; medulloblastoma/PNET, n = 6; ependymoma, n = 1; plexus carcinoma, n = 1) received in a pilot study one course of HDCT with ABSCT. The consolidation regimen consisted of thiotepa (400-600mg/m2/d, i.v. 6 h, d-9), carboplatin and etoposide (500mg/m2/d, CVI 24h, d-8 to d-5, respectively) and was followed by the retransfusion of autologous blood stem cells on day 0. Before starting HDCT 6 patients showed CR and 4 patients had PR or stable disease (SD). Following the HDCT 3 of the 4 patients with residual tumor had CR or PR. 6 patients have remained in continuous CR or SD 8 to 41 months (median 17.2 months) after the HDCT. 2 patients relapsed 8.5 and 9.5 months after HDCT and died from progressive disease. Two patients died therapy-related from systemic aspergillosis and were not evaluable for response. Hematological recovery with an absolute neutrophile count of > 0.5 x 10(9)/l and a platelet count of > 30 x 10(9)/l was reached on days +11 (median; range, +9 to +14) and +16 (median; range, +6 to +47), respectively. The main nonhematological toxic effects were infections, severe mucositis, and hyperbilirubinemia. Although the long-term efficacy of HDCT with ABSCT is still not evaluable and the toxicity of this regimen is high, a multicenter phase II trial seems to be justified in view of the poor prognosis of recurrent or refractory brain tumors in children and adolescents.