henhaobio
Sign in

bioRxivNeurosciencePreprint

Dystrophic changes of nigrostriatal axons harboring a Synj1 Parkinson mutation suggest catastrophic failure of endocytic mechanisms

Yumei WuiD, Peng XuiD, James MoraniD, C. Shan XuiD, Kenneth J. HayworthiD, Mian CaoiD, Lin ShaoiD, Dalton James SurmeieriD, Harald F. HessiD, Pietro V. De CamilliiD

PDFDOIData
In-depth full-text digest available · Jump to digest ↓

Abstract

Synaptojanin 1 is a brain enriched phosphoinositide phosphatase implicated in endocytosis at the synapse. A mutation (R258Q) that selectively impairs its Sac1 phosphatase domain causes early onset familial Parkinsonism. Neurons of mice with this mutation display synaptic vesicle traffic defects across the brain, but selective dystrophic changes in a subset of dopaminergic axons in the dorsolateral striatum. Using correlative light microscopy-FIB-SEM of mutant mouse striata to visualize in 3D these abnormal structures we show that they represent clusters of focal axonal dilations harboring massive, onion-like DAT enriched plasma membrane infoldings, generally localized next to cell bodies of neighboring cells, often engulfing evaginations of such cells. This dysmorphia was associated with a deficit in dopamine release in the same striatal region. Given the involvement of Synj1 in endocytic mechanisms, these structures may reflect an imbalance between exocytosis and endocytosis. Their occurrence only in a subset of axons suggest a vulnerability threshold of these axons beyond which the expansion of the plasma membrane is not counteracted by compensatory mechanisms.

In-depth summary

Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 2 (10 Sept 2026) · CC BY 4.0

Focal dopaminergic axon swellings in the dorsolateral striatum of Synj1 R259Q mutant mice are clusters of DAT-rich, onion-like plasma membrane invaginations, and the same region shows reduced evoked dopamine release.

Earlier work from the same group found abnormal DAT and tyrosine hydroxylase foci in the dorsal striatum of these mice that roughly tracked the abundance of multilamellar whorls seen by electron microscopy, but the two had not been shown to be the same structure. Correlative light and 3D electron microscopy now links them and gives their ultrastructure.

Key results

  1. ShownWhole-brain light-sheet imaging showed the bright tdTomato foci (dystrophic dopaminergic axon segments) concentrated in the dorsolateral striatum of mutant mice. They were nearly absent from the ventral striatum, and their density fell from lateral to medial.

    Threshold-based segmentation of foci in one delipidated brain, shown as 3D and coronal views. The text gives no counts or statistics. Foci were not seen in WT mice at high-power view. · Abnormal foci of tdTomato fluorescence…; Figure legends

  2. ShownCorrelative light and FIB-SEM showed each fluorescent focus is a cluster of interconnected membrane whorls from one axon. The whorls are sheet-like invaginations of the axonal plasma membrane that wrap evaginations of neighbouring cells. They are DAT-positive and continuous with presynaptic active zones.

    Volumes at 8 nm/voxel on a Zeiss Crossbeam 550, and a higher-resolution Janelia instrument for one branched terminal. One large branched mitochondrion extended into several whorls of the same cluster. Conventional TEM showed synaptic vesicles and trapped dense organelles. · Dystrophic foci correspond to membrane whorls…; Membrane whorls derive from massive…; FIB-SEM CLEM at the Yale CCMI facility; FIBSEM at HHMI Janelia Research Campus

  3. ShownDystrophic foci sit next to cell bodies and blood vessels, and wrap evaginations of the neighbouring cell. The neighbours include spiny projection neurons, astrocytes and microglia, so there is no single partner cell type. Foci were mostly not interconnected, which suggests local changes.

    Immunofluorescence for DARPP32, S100b and Iba1 together with DAT; rings of DAT signal had cores positive for markers of the adjacent cell. Qualitative; no proportions are given. · Dystrophic axonal structures are generally…

  4. ShownEvoked dopamine release measured with dLight1.3b was reduced in the dorsolateral striatum of mutant slices but not in the ventral striatum (nucleus accumbens). Repeated burst stimulation produced a progressive drop in release.

    Single pulse: 39% reduction, P = 0.0001 (n=12 slices, N=6 mice vs n=12, N=7 heterozygous controls). Five pulses at 10 Hz: 30% reduction, P < 0.0001 (n=9, N=3 vs n=9, N=4). Ventral striatum release amplitude did not differ, though decay was slower there (tau 290.6 vs 223.8 ms, P < 0.0127). · The Synj1RQ mutation was associated with a…; Figure legends

  5. ShownThe synaptic vesicle proteins SV2C and vMAT2 are concentrated in the dystrophic foci but do not overlap with DAT. This indicates the plasma membrane invagination is distinct from the endocytic recapture of vesicle proteins after exocytosis.

    Double immunofluorescence for DAT with SV2C or vMAT2 in dystrophic foci; qualitative colocalization only. · Synaptic vesicle markers of DAergic neurons are…; DISCUSSION

Methods, data and reproducibility

Mice carrying the Synj1 R259Q knock-in were crossed to a DAT-Cre tdTomato reporter to label dopaminergic axons. Axonal foci were mapped by light-sheet and confocal imaging, resolved by correlative FIB-SEM and TEM, and dopamine release was measured in slices with a fluorescent dopamine sensor and two-photon imaging.

  • DAT-IREScre; Ai9 mice, Synj1 RQ/RQ or WT, aged 1.5 to 15 months, for fluorescence, light-sheet, FIB-SEM and TEM · mouse
  • Ex vivo striatal slices with dLight1.3b, dorsolateral striatum single pulse, Synj1 RQ vs heterozygous controls · mouse · n = n=12 slices, N=6 mice (RQ); n=12, N=7 (control)
  • Ex vivo slices, dorsolateral striatum, five-pulse train at 10 Hz · mouse · n = n=9, N=3 (RQ); n=9, N=4 (control)
  • Key Resource Table listing data, protocols and materials with persistent identifiers · mouse · https://doi.org/10.5281/zenodo.22662279
Methods & tools
dLight1.3b, two-photon laser scanning microscopy, SmartSPIM light-sheet microscopy, FIB-SEM (Zeiss Crossbeam 550, custom Janelia instrument), Zeiss Arivis Pro, Imaris, Dragonfly Pro, 3dmod, Fiji/ImageJ, GraphPad Prism8
Reagents & environment
Software is named but versions are mostly not given (OlyVIA 4.2, Atlas 5 and Prism8 are the exceptions); no container or requirements file.
Reproducibility gaps
Analysis scripts are cited only as BioStudies S-BIAD3429, with no code repository URL; analysis was done in GUI software.
Limitations (4)
  • Dystrophic segments occur in only a minor subpopulation of axons, and it is unclear whether many axons of few neurons or few branches of many neurons are affected. · stated by the authors
  • The mechanisms behind the invaginations and the selective vulnerability of dorsolateral striatum axons are unresolved; the exocytosis/endocytosis imbalance and vesicle-exocytosis shutdown are offered as a favoured model, not tested. · stated by the authors
  • The release deficit is unlikely to be explained by the small fraction of dystrophic axons. The different decay kinetics between dorsolateral and ventral striatum also need further investigation. · stated by the authors
  • Ultrastructural findings come from a few illustrated FIB-SEM volumes and TEM images, and foci density is not quantified. Release controls are heterozygous littermates rather than WT. · noted in this summary

Read this if you study Parkinson's disease genes such as SYNJ1 or auxilin, dopaminergic axon pathology, or correlative light and volume electron microscopy of neuronal membrane structures.

Citations
1

Reproducibility ledger

Nobody has reported trying to reproduce this paper yet. Did you replicate an experiment or run the code? Your report saves the next lab a week.

Sign in to file a reproducibility report.

Related papers

Similarity Map
SelectedSame fieldCross-field
THISNg '23Rafiq '24Zhu '22Lin '25Cao '20Schechter '20
81% semantic matchNeuroscience
Xin Yi Ng, Yumei Wu, Youneng Lin+4 more·npj Parkinson s Disease·Feb 15, 2023· 28 citations