Ankyrin B Promotes Developmental Spine Regulation in the Mouse Prefrontal Cortex

Abstract

Postnatal regulation of dendritic spine formation and refinement in cortical pyramidal neurons is critical for excitatory/inhibitory balance in neocortical networks. Recent studies have identified a selective spine pruning mechanism in the mouse prefrontal cortex (PFC) mediated by class 3 Semaphorins and the L1-CAM cell adhesion molecules Neuron-glia related CAM (NrCAM), Close Homolog of L1 (CHL1), and L1. L1-CAMs bind Ankyrin B (AnkB), an actin-spectrin adaptor encoded by Ankyrin2 (ANK2), a high confidence gene for autism spectrum disorder (ASD). In a new inducible mouse model (Nex1Cre-ERT2: Ank2flox: RCE), Ank2 deletion in early postnatal pyramidal neurons increased spine density on apical dendrites in PFC layer 2/3 of homozygous and heterozygous Ank2-deficient mice. In contrast, Ank2 deletion in adulthood had no effect on spine density. Sema3F-induced spine pruning was impaired in cortical neuron cultures from AnkB-null mice and was rescued by re-expression of the 220 kDa AnkB isoform but not 440 kDa AnkB. AnkB bound to NrCAM at a cytoplasmic domain motif (FIGQY1231), and mutation to FIGQH inhibited binding, impairing Sema3F-induced spine pruning in neuronal cultures. Identification of a novel function for AnkB in dendritic spine regulation provides insight into cortical circuit development, as well as potential molecular deficiencies in ASD.

Synaptic cell adhesion molecules contribute to the pathogenesis and progression of fragile X syndrome

“…It mediates homophilic and heterophilic interactions between neurons ( Kadmon et al, 1990a ; Sytnyk et al, 2017 ; Stoyanova and Lutz, 2022 ) and cooperates with NCAM through a mechanism termed assisted homophilic adhesion ( Kadmon et al, 1990b ). As evidenced in murine model systems, L1-CAM also facilitates axon repulsion and growth cone collapse in response to secreted class 3 Semaphorins (Sema3) ( Mohan et al, 2019b ; Duncan et al, 2021b ), which prune distinct populations of dendritic spines during development and homeostatic scaling ( Mohan et al, 2019a , b ; Murphy et al, 2023a ). Sema3 dimers bind to heterotrimeric receptors comprising L1-CAM, neuropilins (Npn1/2), and plexins A (PlexA1-4), activating intracellular signaling through PlexA Ras-GAP activity that results in spine pruning ( Duncan et al, 2021a ; Murphy et al, 2023a ).…”

“…As evidenced in murine model systems, L1-CAM also facilitates axon repulsion and growth cone collapse in response to secreted class 3 Semaphorins (Sema3) ( Mohan et al, 2019b ; Duncan et al, 2021b ), which prune distinct populations of dendritic spines during development and homeostatic scaling ( Mohan et al, 2019a , b ; Murphy et al, 2023a ). Sema3 dimers bind to heterotrimeric receptors comprising L1-CAM, neuropilins (Npn1/2), and plexins A (PlexA1-4), activating intracellular signaling through PlexA Ras-GAP activity that results in spine pruning ( Duncan et al, 2021a ; Murphy et al, 2023a ). Genetic knockouts of L1-CAM in mice lead to increased density of immature dendritic spines on the apical dendrites of cortical pyramidal neurons ( Murphy et al, 2023b ).…”

“…A review of pertinent studies has revealed that L1-CAM binds Ankyrin B (AnkB) at a conserved cytoplasmic domain motif (FIGQY), an actin-spectrin adaptor encoded by Ankyrin2, a gene with high confidence in relation to ASDs ( Bennett and Healy, 2009 ; Murphy et al, 2023a ). Additionally, L1 knock-in mouse mutants harboring a point mutation at the L1 ankyrin binding site demonstrated augmented spine density in the prefrontal cortex (PFC) ( Murphy et al, 2023b ).…”

“…Using mouse models deficient in L1 family members, Murphy et al investigated the role of L1 and its interaction with AnkB in dendritic spine regulation in L1-null mice. They found that deletion of L1 or mutation of the FIGQY Ankyrin binding site in the cytoplasmic domain of L1 increased the density of spines on apical dendrites of pyramidal neurons in the mouse neocortex ( Murphy et al, 2023a ). Moreover, they rescued cortical neurons with impaired dendritic spine development by re-expression of the 220 kDa AnkB isoform in a new inducible mouse model (Nex1Cre-ERT 2: Ank2flox: RCE) ( Murphy et al, 2023a ).…”

“…They found that deletion of L1 or mutation of the FIGQY Ankyrin binding site in the cytoplasmic domain of L1 increased the density of spines on apical dendrites of pyramidal neurons in the mouse neocortex ( Murphy et al, 2023a ). Moreover, they rescued cortical neurons with impaired dendritic spine development by re-expression of the 220 kDa AnkB isoform in a new inducible mouse model (Nex1Cre-ERT 2: Ank2flox: RCE) ( Murphy et al, 2023a ). The findings of L1 and its interaction with AnkB in dendritic spine regulation provides a new research direction for the association between L1-CAM and neurodevelopmental diseases such as ASD and FXS and reveal potential pharmacological targets.…”