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Sudarsanam, S.

Publications and source records attributed to Sudarsanam, S..

2 recordsLinked to original sources
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

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↗