Kavli Affiliate: Alex Kolodkin
| Authors: Joelle M Dorskind, Sriram Sudarsanam, Randal A Hand, Jakub Ziak, Maame Amoah-Dankwah, Luis Guzman-Clavel, John Lee Soto-Vargas and Alex L Kolodkin
| Summary:
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.