GluD2- and Cbln1-mediated competitive interactions shape the dendritic arbors of cerebellar Purkinje cells

Abstract

The synaptotrophic hypothesis posits that synapse formation stabilizes dendritic branches, yet this hypothesis has not been causally tested in vivo in the mammalian brain. Presynaptic ligand cerebellin-1 (Cbln1) and postsynaptic receptor GluD2 mediate synaptogenesis between granule cells and Purkinje cells in the molecular layer of the cerebellar cortex. Here we show that sparse but not global knockout of GluD2 causes under-elaboration of Purkinje cell dendrites in the deep molecular layer and overelaboration in the superficial molecular layer. Developmental, overexpression, structure-function, and genetic epistasis analyses indicate that dendrite morphogenesis defects result from competitive synaptogenesis in a Cbln1/GluD2-dependent manner. A generative model of dendritic growth based on competitive synaptogenesis largely recapitulates GluD2 sparse and global knockout phenotypes. Our results support the synaptotrophic hypothesis at initial stages of dendrite development, suggest a second mode in which cumulative synapse formation inhibits further dendrite growth, and highlight the importance of competition in dendrite morphogenesis.

Maturation of Purkinje cell firing properties relies on neurogenesis of excitatory neurons

“…Sholl analysis revealed that the Purkinje cells in the mutants were smaller with less bifurcated dendritic branches ( Figure 3B–C ). Furthermore, spine density was significantly lower in En1 Cre/+ ;Atoh1 fl/- mice compared to the control mice ( Figure 3D–E ), which is in agreement with previous work showing that dendrite outgrowth is dependent on the formation of excitatory synapses, the majority of which are contributed from granule cell parallel fibers in control animals ( Bradley and Berry, 1976 ; Pan et al, 2009 ; Park et al, 2019 ; Takeo et al, 2021 ). From these data, we conclude that Purkinje cells in the P14 En1 Cre/+ ;Atoh1 fl/- mice have less morphological complexity.…”

“…Previous studies suggest that decreasing excitatory input alters Purkinje cell dendrite outgrowth ( Bradley and Berry, 1976 ; Pan et al, 2009 ; Park et al, 2019 ; Takeo et al, 2021 ), which results in abnormal dendrite morphology in agranular mice ( Sotelo and Dusart, 2009 ). Therefore, we next investigated the cellular morphology of Purkinje cells in control and En1 Cre/+ ;Atoh1 fl/- mice by staining mouse brains using a modified Golgi-Cox method.…”

Cbln1 directs axon targeting by corticospinal neurons specifically toward thoraco-lumbar spinal cord

“…This peak coincides with the period when CSN TL axons extend past the cervical cord toward thoraco-lumbar segments. This time course of significant differential expression along with known roles for Cbln1 and its family members in synaptogenesis (Hirai et al, 2005;Stevens et al, 2007;Kusnoor et al, 2010;Matsuda et al, 2010;Uemura et al, 2010;Ibata et al, 2019;Takeo et al, 2021) suggested that Cbln1 might function in controlling these processes by some or all CSN medial .…”

“…Cbln1 is a member of the C1q superfamily, which includes proteins critically essential for normal function of the immune and nervous systems (Ghai et al, 2007; Stevens et al, 2007; Yuzaki, 2011). Cbln1 has been extensively characterized in the cerebellum, where it is required for synapse formation and synapse stabilization between parallel fibers of granule cells and Purkinje cell dendrites (Hirai et al, 2005; Matsuda et al, 2010; Uemura et al, 2010; Elegheert et al, 2016; Ibata et al, 2019; Takeo et al, 2021). More recently, it also has been shown to play roles in synapse formation in the striatum and the hippocampus (Kusnoor et al, 2010; Seigneur and Südhof, 2018).…”

The angiopoietin-Tie2 pathway regulates Purkinje cell dendritic morphogenesis in a cell-autonomous manner

“…Consistent with increased spine density, mEPSC frequency was also increased in PCs of Pcp2Cre;Tie2 flox/flox mice. Interestingly, cumulative synapse formation has been shown to inhibit dendritic growth ( Takeo et al, 2021 ). Thus, it is possible that the decrease in dendritic complexity could be partially due to an increase in synapse number.…”