Biology subjects

Fujise, K.

Publications and source records attributed to Fujise, K..

4 recordsLinked to original sources

bioRxiv2024

Overlapping role of synaptophysin and synaptogyrin family proteins in determining the small size of synaptic vesicles

Members of the synaptophysin and synaptogyrin family are vesicle proteins with four transmembrane domains. In spite of their abundance in synaptic vesicle (SV) membranes, their role remains elusive and only mild defects at the cellular and organismal level are observed in mice lacking one or more family members. Here, we show that co-expression with synapsin of each of the four brain-enriched members of this family - synaptophysin, synaptoporin, synaptogyrin1 and synaptogyrin3 - in fibroblasts is sufficient to generate clusters of small vesicles in the same size range of SVs. Moreover, mice lacking all these four proteins have larger SVs. We conclude that synaptophysin and synaptogyrin family proteins play an overlapping function in the biogenesis of SVs and in determining their small size.

neuroscience↗

bioRxiv2024

Synaptic vesicle characterization of iPSC-derived dopaminergic neurons provides insight into distinct secretory vesicle pools

The impairment of dopaminergic (DA) neurons plays a central role in the development of Parkinsons disease. Evidence for distinct populations of synaptic vesicles (SVs) differing in neurotransmitter content (glutamate versus dopamine) has been attributed to differences in trafficking pathways and their exocytosis kinetics. However, the molecular and ultrastructural organization of the two types of vesicles remains poorly understood. Here we examined the development of axonal varicosities in human iPSC-derived DA neurons and glutamatergic neurons (i3Neurons). While i3Neurons are comprised of 40-50 nm small clear SVs, DA neurons are predominantly comprised of large pleiomorphic vesicles including empty and dense core vesicles, in addition to the classical SVs. The large vesicles were positive for VMAT2, the monoamine vesicular transporter responsible for loading dopamine, and are distinctly larger in size and spatially segregated from the VGLUT1/2-positive vesicles when expressed in an ectopic SV-like organelle reconstitution system. Moreover, these VMAT2-positive vesicles were also colocalized to known SV markers such as Rab3, SCAMP5, VAMP2, SV2C and can be clustered by the matrix protein synapsin. Our results show that DA neurons display inherent differences in their populations of neurotransmitter-containing secretory vesicles, and iPSC-derived neurons are powerful models for the study of presynaptic structures.

neuroscience↗

bioRxiv2023

Parkinsonism Sac domain mutation in Synaptojanin-1 affects ciliary properties in iPSC-derived dopaminergic neurons

Synaptojanin-1 (SJ1) is a major neuronal-enriched PI(4,5)P2 4- and 5-phosphatase implicated in the shedding of endocytic factors during endocytosis. A mutation (R258Q) that impairs selectively its 4-phosphatase activity causes Parkinsonism in humans and neurological defects in mice (SJ1RQKI mice). Studies of these mice showed, besides an abnormal assembly state of endocytic factors at synapses, the presence of dystrophic nerve terminals selectively in a subset of nigro-striatal dopamine (DA)-ergic axons, suggesting a special lability of DA neurons to the impairment of SJ1 function. Here we have further investigated the impact of SJ1 on DA neurons using iPSC-derived SJ1 KO and SJ1RQKI DA neurons and their isogenic controls. In addition to the expected enhanced clustering of endocytic factors in nerve terminals, we observed in both SJ1 mutant neuronal lines increased cilia length. Further analysis of cilia of SJ1RQDA neurons revealed abnormal accumulation of the Ca2+ channel Cav1.3 and of ubiquitin chains, suggesting an impaired clearing of proteins from cilia which may result from an endocytic defect at the ciliary base, where a focal concentration of SJ1 was observed. We suggest that SJ1 may contribute to the control of ciliary protein dynamics in DA neurons, with implications on cilia-mediated signaling.

neuroscience↗

bioRxiv2021

Imaging-based evaluation of pathogenicity by novel DNM2 variants associated with centronuclear myopathy

Centronuclear myopathy (CNM) is characterized clinically by muscle weakness and pathologically by the presence of centralized nuclei and disarrangement of T-tubules in muscle fibers. DNM2 which encodes a large GTPase dynamin 2 have been identified as a causative gene for CNM. Nevertheless, the identification of DNM2 variants may not always lead to the definitive diagnosis as their pathogenicity is often unknown. In this study, by imaging T-tubule-like structures reconstituted in cellulo, we demonstrated that aberrant membrane remodeling by mutant dynamin 2 is tightly associated with gain-of-function features of DNM2 variants. This simple in cellulo assay provided quantitative data required for accurately evaluating pathogenicity of reported and novel DNM2 variants identified from CNM patients in our cohort. Our approaches combining the in cellulo assay with clinical information of the patients enabled to explain the course of a disease progression by pathogenesis of each variant in DNM2-associated CNM.

cell biology↗