Ca_v2.1 in Cerebellar Purkinje Cells Regulates Competitive Excitatory Synaptic Wiring, Cell Survival, and Cerebellar Biochemical Compartmentalization

Abstract

In the adult cerebellum, each Purkinje cell (PC) is innervated by a single climbing fiber (CF) in proximal dendrites and 10 -106 parallel fibers (PFs) in distal dendrites. This organized wiring is established postnatally through heterosynaptic competition between PFs and CFs and homosynaptic competition among multiple CFs. Using PC-specific Ca v 2.1 knock-out mice (PC-Ca v 2.1 KO mice), we have demonstrated recently that postsynaptic Ca v 2.1 plays a key role in the homosynaptic competition by promoting functional strengthening and dendritic translocation of single "winner" CFs. Here, we report that Ca v 2.1 in PCs, but not in granule cells, is also essential for the heterosynaptic competition. In PC-Ca v 2.1 KO mice, the extent of CF territory was limited to the soma and basal dendrites, whereas PF territory was expanded reciprocally. Consequently, the proximal somatodendritic domain of PCs displayed hyperspiny transformation and fell into chaotic innervation by multiple CFs and numerous PFs. PC-Ca v 2.1 KO mice also displayed patterned degeneration of PCs, which occurred preferentially in aldolase C/zebrin II-negative cerebellar compartments. Furthermore, the mutually complementary expression of phospholipase C␤3 (PLC␤3) and PLC␤4 was altered such that their normally sharp boundary was blurred in the PCs of PC-Ca v 2.1 KO mice. This blurring was caused by an impaired posttranscriptional downregulation of PLC␤3 in PLC␤4-dominant PCs during the early postnatal period. A similar alteration was noted in the banded expression of the glutamate transporter EAAT4 in PC-Ca v 2.1 KO mice. Therefore, Ca v 2.1 in PCs is essential for competitive synaptic wiring, cell survival, and the establishment of precise boundaries and reciprocity of biochemical compartments in PCs.

Mature Purkinje Cells Require the Retinoic Acid-Related Orphan Receptor-α (RORα) to Maintain Climbing Fiber Mono-Innervation and Other Adult Characteristics

“…Nevertheless, the regressive morphological processes that these PC dendritic trees undergo, by suppressing the vast majority of tertiary spines, create an abnormal situation for adult PCs in which the partition of dendritic territory between PFs and CFs is disturbed. This situation is similar to that described for PCCa v 2.1 KO mice, in which the extent of CF territory was limited to the soma and basal dendrites, whereas PF territory was expanded (Miyazaki et al, 2012). However, in late rora-deleted PCs, we do not observe the hyperspiny transformation of the PC proximal somatodendritic domain to the extent described in PC-Ca v 2.1 mutants.…”

Synapse type-independent degradation of the endocannabinoid 2-arachidonoylglycerol after retrograde synaptic suppression

“…To clarify the contribution of MGL in PF terminals to the regulation of DSE, we generated mice with GC-specific deletion of MGL (GC-specific MGL-KO mice) and examined DSE at CF-PC and PF-PC synapses. To obtain a GC-specific Cre recombinase expression, we used a E3CreN line (GluN2C +/iCre ), the Cre gene of which was expressed in GCs under the control of a GluN2C (GluRɛ3) promoter (41). By intercrossing MGLfloxed (MGL lox/lox ) mice with the E3CreN line, we created GC-specific MGL-KO mice.…”

“…Global MGL-KO mice were generated as described previously (35). GC-specific MGL-KO mice were obtained by crossing MGL lox/lox with an E3CreN line (GluN2C +/iCre ) whose Cre gene was expressed in GCs under the control of a GluN2C (GluRɛ3) promoter (41).…”

Territories of heterologous inputs onto Purkinje cell dendrites are segregated by mGluR1-dependent parallel fiber synapse elimination

“…P/Q-type VDCC-KO mice exhibit more severe defects in CF synapse development than mutant mice deficient in the mGluR1 signaling pathway. P/Q-type VDCC-KO mice are impaired in selective functional strengthening and dendritic translocation of single winner CFs, resulting in a diminished territory by winner CFs and abnormal persistence of weaker CFs and PFs in the same somatodendritic compartment (9)(10)(11). Therefore, local and global Ca 2+ dynamics, which are mediated by the mGluR1 signaling pathway and P/Q-type VDCCs, respectively, may work in concert to drive CF synapse elimination from the soma and PF synapse elimination from proximal dendrites.…”

“…The strengthened ("winner") CF starts dendritic translocation, whereas the other weaker ("loser") CFs remaining on the soma are eliminated (6)(7)(8). In this process, P/Q-type voltage-dependent Ca 2+ channels (VDCCs) promote functional differentiation and dendritic translocation of winner CFs, and the early phase of CF synapse elimination (9)(10)(11), whereas the late phase of CF synapse elimination is critically dependent on the formation of parallel fiber (PF) synapses and activation of the type 1 metabotropic glutamate receptor (mGluR1)-protein kinase Cγ (PKCγ) pathway (12)(13)(14)(15)(16)(17).…”