Gjd2b-mediated gap junctions promote glutamatergic synapse formation and dendritic elaboration in Purkinje neurons

AbstractGap junctions between neurons serve as electrical synapses, in addition to conducting metabolites and signaling molecules. These functions of gap junctions have led to the idea that during development, gap junctions could prefigure chemical synapses. We present evidence for this idea at a central, glutamatergic synapse and provide some mechanistic insights. Here, we show that reduction or loss of Gjd2b-containing gap junctions led to a decrease in glutamatergic synapse density in cerebellar Purkinje neurons (PNs) in larval zebrafish. Gjd2b-/- larvae exhibited faster mEPSCs and a consistent decrease in dendritic arbor size. These PNs also showed decreased branch elongations but normal rate of branch retractions. Further, the dendritic growth deficits in gjd2b-/- mutants were rescued by expressing full length Gjd2b in single PNs. This suggests that Gjd2b may form heterotypic channels with other connexins in gjd2b-/- larvae, though it is not clear if PNs in wild type animals make homotypic or heterotypic gap junction channels. Dendritic growth deficits were not rescued by expressing a deletion mutant of Gjd2b unable to form functional channels. Finally, the expression levels of five isoforms of camkii were increased in gjd2b-/- larvae and inhibition of CaMKII restored dendritic arbor lengths of mutant larvae to wild type levels. These results suggest a link between signaling via Gjd2b-containing gap junctions, CaMKII function and dendritic growth. In sum, our results demonstrate that Gjd2b-mediated gap junctions are key regulators of glutamatergic synapse formation and dendritic elaboration in PNs.

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Gjd2b-mediated gap junctions promote glutamatergic synapse formation and dendritic elaboration in Purkinje neurons

eLife ◽

10.7554/elife.68124 ◽

2021 ◽

Vol 10 ◽

Author(s):

Sahana Sitaraman ◽

Gnaneshwar Yadav ◽

Vandana Agarwal ◽

Shaista Jabeen ◽

Shivangi Verma ◽

...

Keyword(s):

Gap Junctions ◽

Synapse Formation ◽

Molecular Layer ◽

Time Lapse ◽

Purkinje Neurons ◽

Glutamatergic Synapse ◽

Junction Protein ◽

Synapse Density ◽

Chemical Synapses ◽

Cerebellar Purkinje Neurons

Gap junctions between neurons serve as electrical synapses, in addition to conducting metabolites and signaling molecules. During development, early-appearing gap junctions are thought to prefigure chemical synapses, which appear much later. We present evidence for this idea at a central, glutamatergic synapse and provide some mechanistic insights. Loss or reduction in the levels of the gap junction protein Gjd2b decreased the frequency of glutamatergic miniature excitatory postsynaptic currents (mEPSCs) in cerebellar Purkinje neurons (PNs) in larval zebrafish. Ultrastructural analysis in the molecular layer showed decreased synapse density. Further, mEPSCs had faster kinetics and larger amplitudes in mutant PNs, consistent with their stunted dendritic arbors. Time-lapse microscopy in wild type and mutant PNs reveals that Gjd2b puncta promote the elongation of branches and that CaMKII may be a critical mediator of this process. These results demonstrate that Gjd2b-mediated gap junctions regulate glutamatergic synapse formation and dendritic elaboration in PNs.

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Restricted occurrence of an unusual ganglioside GD1? in rat brain and its possible involvement in dendritic growth of cerebellar Purkinje neurons

Journal of Neuroscience Research ◽

10.1002/(sici)1097-4547(19960401)44:1<73::aid-jnr10>3.0.co;2-9 ◽

1996 ◽

Vol 44 (1) ◽

pp. 73-83 ◽

Cited By ~ 7

Author(s):

S. Furuya ◽

T. Hashikawa ◽

Y. Hirabayashi

Keyword(s):

Rat Brain ◽

Dendritic Growth ◽

Purkinje Neurons ◽

Cerebellar Purkinje Neurons

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Calmodulin limits pathogenic Na+ channel persistent current

The Journal of General Physiology ◽

10.1085/jgp.201611721 ◽

2017 ◽

Vol 149 (2) ◽

pp. 277-293 ◽

Cited By ~ 31

Author(s):

Haidun Yan ◽

Chaojian Wang ◽

Steven O. Marx ◽

Geoffrey S. Pitt

Keyword(s):

Cardiac Arrhythmias ◽

Persistent Current ◽

Purkinje Neurons ◽

Na Channel ◽

Wild Type ◽

Na Current ◽

Voltage Gated ◽

Nav Channels ◽

Cerebellar Purkinje Neurons ◽

Terminal Domains

Increased “persistent” current, caused by delayed inactivation, through voltage-gated Na+ (NaV) channels leads to cardiac arrhythmias or epilepsy. The underlying molecular contributors to these inactivation defects are poorly understood. Here, we show that calmodulin (CaM) binding to multiple sites within NaV channel intracellular C-terminal domains (CTDs) limits persistent Na+ current and accelerates inactivation across the NaV family. Arrhythmia or epilepsy mutations located in NaV1.5 or NaV1.2 channel CTDs, respectively, reduce CaM binding either directly or by interfering with CTD–CTD interchannel interactions. Boosting the availability of CaM, thus shifting its binding equilibrium, restores wild-type (WT)–like inactivation in mutant NaV1.5 and NaV1.2 channels and likewise diminishes the comparatively large persistent Na+ current through WT NaV1.6, whose CTD displays relatively low CaM affinity. In cerebellar Purkinje neurons, in which NaV1.6 promotes a large physiological persistent Na+ current, increased CaM diminishes the persistent Na+ current, suggesting that the endogenous, comparatively weak affinity of NaV1.6 for apoCaM is important for physiological persistent current.

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Regional and genotypic differences in intrinsic electrophysiological properties of cerebellar Purkinje neurons from wild-type and dystrophin-deficient mdx mice

Neurobiology of Learning and Memory ◽

10.1016/j.nlm.2013.10.017 ◽

2014 ◽

Vol 107 ◽

pp. 19-31 ◽

Cited By ~ 10

Author(s):

Wanda M. Snow ◽

Judy E. Anderson ◽

Mark Fry

Keyword(s):

Purkinje Neurons ◽

Mdx Mice ◽

Genotypic Differences ◽

Wild Type ◽

Electrophysiological Properties ◽

Cerebellar Purkinje Neurons

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BDNF mobilizes synaptic vesicles and enhances synapse formation by disrupting cadherin–β-catenin interactions

The Journal of Cell Biology ◽

10.1083/jcb.200601087 ◽

2006 ◽

Vol 174 (2) ◽

pp. 289-299 ◽

Cited By ~ 115

Author(s):

Shernaz X. Bamji ◽

Beatriz Rico ◽

Nikole Kimes ◽

Louis F. Reichardt

Keyword(s):

Synaptic Vesicle ◽

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Molecular Mechanisms ◽

Synapse Formation ◽

Time Lapse ◽

Synapse Density ◽

Vesicle Mobility ◽

Small Clusters ◽

Vertebrate Central Nervous System

Neurons of the vertebrate central nervous system have the capacity to modify synapse number, morphology, and efficacy in response to activity. Some of these functions can be attributed to activity-induced synthesis and secretion of the neurotrophin brain-derived neurotrophic factor (BDNF); however, the molecular mechanisms by which BDNF mediates these events are still not well understood. Using time-lapse confocal analysis, we show that BDNF mobilizes synaptic vesicles at existing synapses, resulting in small clusters of synaptic vesicles “splitting” away from synaptic sites. We demonstrate that BDNF's ability to mobilize synaptic vesicle clusters depends on the dissociation of cadherin–β-catenin adhesion complexes that occurs after tyrosine phosphorylation of β-catenin. Artificially maintaining cadherin–β-catenin complexes in the presence of BDNF abolishes the BDNF-mediated enhancement of synaptic vesicle mobility, as well as the longer-term BDNF-mediated increase in synapse number. Together, this data demonstrates that the disruption of cadherin–β-catenin complexes is an important molecular event through which BDNF increases synapse density in cultured hippocampal neurons.

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