Biology subjects

Kolodkin, A. L.

Publications and source records attributed to Kolodkin, A. L..

10 recordsLinked to original sources

bioRxiv2026

The mechanotransduction channel Piezo2 refines axonal projections to the accessory optic system and regulates the optokinetic reflex

The optokinetic reflex (OKR) is an evolutionarily conserved reflexive behavior that ensures image stabilization on the retina during global motion. It consists of smooth eye tracking movements in the direction of the moving stimulus interspersed with rapid resetting saccades. This reflex is driven by retinal ON direction-selective ganglion cells (oDSGCs), which comprise distinct subtypes tuned either to vertical or horizontal motion. oDSGCs convey directional signals to the brain via precise axonal projections to specific accessory optic system (AOS) nuclei. However, the mechanisms that establish and maintain the specificity of these circuits remain poorly understood. Here, we identify a critical role for the mechanosensitive ion channel Piezo2 in refining AOS circuitry to ensure appropriate eye movement responses. Single-cell transcriptomic profiling revealed selective enrichment of Piezo2 in horizontally-tuned oDSGCs. We show that both loss and hyperactivation of Piezo2 in retinal neurons leads to cross-coupling of horizontal and vertical OKR responses, producing aberrant diagonal eye tracking movements during horizontal optokinetic stimulation. Mechanistically, Piezo2 regulates the developmental refinement of oDSGC axonal projections within the AOS, and disruption of this process results in persistent ectopic innervation that enables aberrant crosstalk between horizontal and vertical motion pathways. These findings reveal a channel activity-dependent mechanism that ensures the functional segregation of directional motion circuits underlying gaze stabilization. HIGHLIGHTSO_LIPiezo2 is selectively expressed in forward-tuned ON and ON-OFF DSGCs that innervate the accessory optic system C_LIO_LIBoth loss and overactivation of Piezo2 induce cross-coupling of horizontal and vertical optokinetic reflexes C_LIO_LIPiezo2 function in ON-OFF DSGCs is dispensable for normal optokinetic reflex responses C_LIO_LIRetinal Piezo2 refines axonal targeting to the accessory optic system nuclei, ensuring proper optokinetic reflex function C_LI

neuroscience↗

bioRxiv2026

Protein tyrosine phosphatase receptor type kappa (PTPRκ) regulates Superior ON-Direction Selective Ganglion Cell development, facilitating image stabilization

In vertebrates, gaze stabilization during global visual motion requires ON direction-selective ganglion cells (oDSGCs) in the Accessory Optic System (AOS) to drive the optokinetic reflex (OKR). Three types of oDSGCs form independent mosaics; however, the mechanisms that specify and maintain their numbers to create these mosaics during development remain unknown. Here, we identify protein tyrosine phosphatase receptor type kappa (Ptprk) as a key regulator of Superior oDSGC density, the subtype tuned to upward motion. High-depth single-cell RNA sequencing (scRNAseq) reveals that Ptprk is selectively enriched in Superior oDSGCs compared to Inferior oDSGCs, which detect downward motion. Genetic deletion of Ptprk selectively halves the number of Superior oDSGCs while preserving the number of Inferior oDSGCs. Anatomically, Superior oDSGCs in Ptprk mutants exhibit compensatory neurite remodeling to preserve mosaics. Physiologically, oDSGCs have broader tuning curves, and a subset of Superior oDSGCS have aberrant preferred directions in Ptprk mutants. Postsynaptically, loss of Ptprk reduces oDSGC connectivity to central targets. Behaviorally, the OKR responses to upward motion are attenuated in both global and pan-retinal Ptprk mutants, confirming a retinal role for Ptprk in upward image stabilization. Together, these findings demonstrate that the density of a retinal ganglion cell type is under molecular control, and that reducing density drives neurite remodeling, alters circuit computation, and ultimately impairs visually-guided behavior.

neuroscience↗

bioRxiv2025

Cell-type-selective synaptogenesis during the development of excitatory connectivity in the mammalian neocortex

The function of mammalian neocortex relies on the timing of axon extension and establishment of cell-type-biased patterns of excitatory synaptic connections. A subtype of excitatory neurons, layer 6 corticothalamic neurons (L6CThNs), ultimately exhibit a marked preference for synapsing onto parvalbumin-positive (PV) inhibitory interneurons over more common excitatory cells in layers 6 and 4 (L6, L4). We show that the intracortical axons of L6CThNs develop in phases, elongating within L6, then pausing before extending translaminar branches into L4. Decreasing L6CThN excitability selectively enhanced axon growth in L6 but not later elaboration in L4. For both layers, we tested whether preferential synaptogenesis onto rarer PV interneurons, or promiscuous synapse formation followed by selective pruning, generated adult connectivity. We found that L6CThNs formed functional AMPA-receptor-containing synapses preferentially onto PV interneurons. Silent L6CThN synapses were not detected. Our findings show that cell-type-biased synaptogenesis underlies the formation of functional cell-type-specific excitatory connections in the neocortex.

neuroscience↗

bioRxiv2025

Temporally-segregated dual functions for Gfi1 in the development of retinal direction-selectivity

There is great diversity in retinal ganglion cells subtypes in the mouse retina, but little is known about the molecular factors required to generate this subtype diversity. Here, we identify the transcription factor Gfi1 as a conserved driver of differentiation specifically in two downward-tuned direction selective ganglion cells (DSGCs). Further, we describe a post-differentiation role for Gfi1 in regulating dendritic development of Down ON-type DSGCs crucial for their ability to detect downward motion. These results define novel temporally-segregated dual functions for Gfi1 in the development of retinal direction-selective circuits, and they provide a framework for understanding fundamental mechanisms underlying direction-selectivity in the retina.

neuroscience↗

bioRxiv2025

Mef2c Controls Postnatal Callosal Axon Targeting by Regulating Sensitivity to Ephrin Repulsion

Cortical connectivity is contingent on ordered emergence of neuron subtypes followed by the formation of subtype-specific axon projections. Intracortical circuits, including long-range callosal projections, are crucial for information processing, but mechanisms of intracortical axon targeting are still unclear. We find that the transcription factor Myocyte enhancer factor 2-c (Mef2c) directs the development of somatosensory cortical (S1) layer 4 and 5 pyramidal neurons during embryogenesis. During early postnatal development, Mef2c expression shifts to layer 2/3 callosal projection neurons (L2/3 CPNs), and we find a novel function for Mef2c in targeting homotopic contralateral cortical regions by S1-L2/3 CPNs. We demonstrate, using functional manipulation of EphA-EphrinA signaling in Mef2c-mutant CPNs, that Mef2c downregulates EphA6 to desensitize S1-L2/3 CPN axons to EphrinA5-repulsion at their contralateral targets. Our work uncovers dual roles for Mef2c in cortical development: regulation of laminar subtype specification during embryogenesis, and axon targeting in postnatal callosal neurons. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/634300v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@108c788org.highwire.dtl.DTLVardef@163c6c3org.highwire.dtl.DTLVardef@18e6d8borg.highwire.dtl.DTLVardef@1b9f9e4_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIMef2c is required for the development of L4 and L5 neurons in the embryonic neocortex C_LIO_LIPostnatally, Mef2c is enriched in L2/3 neurons and is required for axon targeting C_LIO_LIL2/3-specific Mef2c deletion leads to EphA6 upregulation C_LIO_LIMef2c deletion in L2/3 neurons sensitizes them to EfnA5 repulsion in the contralateral cortex C_LI

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bioRxiv2023

Semaphorin 6A in Retinal Ganglion Cells Regulates Functional Specialization of the Inner Retina

To form functional circuits, neurons must settle in their appropriate cellular locations and then project and elaborate neurites to contact their target synaptic neuropils. Laminar organization within the vertebrate retinal inner plexiform layer (IPL) facilitates pre- and postsynaptic neurite targeting, yet, the precise mechanisms underlying establishment of functional IPL subdomains are not well understood. Here we explore mechanisms defining the compartmentalization of OFF and ON neurites generally, and OFF and ON direction-selective neurites specifically, within the developing IPL. We show that semaphorin 6A (Sema6A), a repulsive axon guidance cue, is required for delineation of OFF versus ON circuits within the IPL: in the Sema6a null IPL, the boundary between OFF and ON domains is blurred. Furthermore, Sema6A expressed by retinal ganglion cells (RGCs) directs laminar segregation of OFF and ON starburst amacrine cell (SAC) dendritic scaffolds, which themselves serve as a substrate upon which other retinal neurites elaborate. These results demonstrate for the first time that RGCs, the first neuron-type born within the retina, play an active role in functional specialization of the IPL. Retinal ganglion cell-dependent regulation of OFF and ON starburst amacrine cell dendritic scaffold segregation prevents blurring of OFF versus ON functional domains in the murine inner plexiform layer.

neuroscience↗

bioRxiv2023

MAP1B Regulates Cortical Neuron Interstitial Axon Branching Through the Tubulin Tyrosination Cycle

Regulation of directed axon guidance and branching during development is essential for the generation of neuronal networks. However, the molecular mechanisms that underlie interstitial axon branching in the mammalian brain remain unresolved. Here, we investigate interstitial axon branching in vivo using an approach for precise labeling of layer 2/3 callosal projection neurons (CPNs), allowing for quantitative analysis of axonal morphology at high acuity and also manipulation of gene expression in well-defined temporal windows. We find that the GSK3{beta} serine/threonine kinase promotes interstitial axon branching in layer 2/3 CPNs by releasing MAP1B-mediated inhibition of axon branching. Further, we find that the tubulin tyrosination cycle is a key downstream component of GSK3{beta}/MAP1B signaling. We propose that MAP1B functions as a brake on axon branching that can be released by GSK3{beta} activation, regulating the tubulin code and thereby playing an integral role in sculpting cortical neuron axon morphology. HIGHLIGHTS- GSK3{beta} activation induces excessive interstitial axon branching in excitatory cortical neurons - MAP1B, acting as a brake, is a downstream effector of GSK3{beta}-mediated axon branching - MAP1B inhibition of axon branching is released by GSK3{beta} phosphorylation - GSK3{beta}/MAP1B regulation of interstitial axon branching is through modification of the tubulin code

neuroscience↗

bioRxiv2023

A semi-automated method for quantifying optokinetic reflex tracking acuity

The study of murine behavioral responses to visual stimuli is a key component of understanding mammalian visual circuitry. One notable response is the optokinetic reflex (OKR), a highly conserved innate behavior necessary for image stabilization on the retina. The OKR provides a robust readout of image tracking ability and has been extensively studied to understand the logic of visual system circuitry and function in mice from different genetic backgrounds. The OKR consists of two phases: a slow tracking phase as the eye follows a stimulus to the edge of the visual plane, and a compensatory fast phase saccade that maintains the image within the visual field. Assessment of the OKR has previously relied on counting individual compensatory eye saccades to estimate tracking speed. To obtain a more direct quantification of tracking ability, we have developed a novel, semi-automated analysis program that allows for rapid and reproducible quantification of unidirectional tracking gains, in addition to being adaptable to any video-oculography equipment. Our analysis program allows for the selection of slow tracking phases, modeling of the vertical and horizontal eye vectors, quantification of eye movement relative to the stimulus, and organization of resultant data into a usable spreadsheet for statistical and graphical comparisons. This quantitative and streamlined analysis pipeline provides a faster and more direct measurement of OKR responses, thereby facilitating further study of visual behavior responses. SUMMARYWe describe here a semi-automated quantitative analysis method that directly measures eye tracking resulting from murine visual system responses to two-dimensional image motion. A Python-based user interface and analysis algorithm allows for higher throughput and more quantitative measurements of eye tracking parameters than previous methods.

neuroscience↗

bioRxiv2023

Drebrin Regulates Collateral Axon Branching in Cortical Layer II/III Somatosensory Neurons

Proper cortical lamination is essential for cognition, learning, and memory. Within the somatosensory cortex, pyramidal excitatory neurons elaborate axon collateral branches in a laminar-specific manner that dictates synaptic partners and overall circuit organization. Here, we leverage mouse models, single-cell labeling and imaging approaches to identify intrinsic regulators of laminar-specific collateral, also termed interstitial, axon branching. We developed new approaches for the robust, sparse, labeling of layer II/III pyramidal neurons to obtain single-cell quantitative assessment of axon branch morphologies. We combined these approaches with cell-autonomous loss-of-function (LOF) and over-expression (OE) manipulations in an in vivo candidate screen to identify regulators of cortical neuron axon branch lamination. We identify a role for the cytoskeletal binding protein drebrin (Dbn1) in regulating layer II/III cortical projection neuron (CPN) collateral axon branching in vitro. LOF experiments show that Dbn1 is necessary to suppress the elongation of layer II/III CPN collateral axon branches within layer IV, where axon branching by layer II/III CPNs is normally absent. Conversely, Dbn1 OE produces excess short axonal protrusions reminiscent of nascent axon collaterals that fail to elongate. Structure-function analyses implicate Dbn1S142 phosphorylation and Dbn1 protein domains known to mediate F-actin bundling and microtubule (MT) coupling as necessary for collateral branch initiation upon Dbn1 OE. Taken together, these results contribute to our understanding of the molecular mechanisms that regulate collateral axon branching in excitatory CPNs, a key process in the elaboration of neocortical circuit formation. Significance StatementLaminar-specific axon targeting is essential for cortical circuit formation. Here, we show that the cytoskeletal protein drebrin (Dbn1) regulates excitatory layer II/III cortical projection neuron (CPN) collateral axon branching, lending insight into the molecular mechanisms that underlie neocortical laminar-specific innervation. To identify branching patterns of single cortical neurons in vivo, we have developed tools that allow us to obtain detailed images of individual CPN morphologies throughout postnatal development and to manipulate gene expression in these same neurons. Our results showing that Dbn1 regulates CPN interstitial axon branching both in vivo and in vitro and may aid in our understanding of how aberrant cortical neuron morphology contributes to dysfunctions observed in Autism Spectrum Disorder (ASD) and epilepsy.

neuroscience↗

bioRxiv2022

Palmitoylation regulates neuropilin-2 localization and function in cortical neurons and conveys specificity to semaphorin signaling via palmitoyl acyltransferases

Secreted semaphorin 3F (Sema3F) and semaphorin 3A (Sema3A) exhibit remarkably distinct effects on deep layer excitatory cortical pyramidal neurons; Sema3F mediates dendritic spine pruning, whereas Sema3A promotes the elaboration of basal dendrites. Sema3F and Sema3A signal through distinct holoreceptors that include neuropilin-2 (Nrp-2)/plexinA3 (PlexA3) and neuropilin-1 (Nrp-1)/PlexA4, respectively. We find that Nrp-2 and Nrp-1 are S-palmitoylated in cortical neurons and that palmitoylation of select Nrp-2 cysteines is required for its proper subcellular localization and also for Sema3F/Nrp-2-dependent dendritic spine pruning in cortical neurons, both in vitro and in vivo. Moreover, we show that the palmitoyl acyltransferase DHHC15 is required for Nrp-2 palmitoylation and Sema3F/Nrp-2-dependent dendritic spine pruning, but it is dispensable for Nrp-1 palmitoylation and Sema3A/Nrp-1-dependent basal dendritic elaboration. Therefore, palmitoyl acyltransferase-substrate specificity is essential for establishing compartmentalized neuronal structure and functional responses to extrinsic guidance cues. HIGHLIGHTSO_LINeuropilins (Nrps) are S-palmitoylated in vitro and in vivo in the central nervous system C_LIO_LIS-palmitoylation of select Nrp-2 cysteines confers subcellular localization specificity and is required for semaphorin 3F-dependent dendritic spine pruning in cortical neurons C_LIO_LIDistinct palmitoyl acyltransferases mediate Nrp-2 and Nrp-1 palmitoylation and function, imparting specificity to semaphorin signaling C_LI

neuroscience↗