Biology subjects

Crapart, C.

Publications and source records attributed to Crapart, C..

3 recordsLinked to original sources

bioRxiv2025

Endoplasmic Reticulum Geometry Dictates Neuronal Bursting via Calcium Store Refill Rates

The endoplasmic reticulum (ER)s continuous morphology is tightly controlled by ER-shaping proteins, whose genetic or expression defects drive a spectrum of neurodegenerative disorders from Hereditary Spastic Paraplegia to Alzheimers disease. Why perturbations in ER morphology manifest specifically in neurons remains unknown. Here, by coupling visualisation of global sub-Hz firing bursts to ER ultrastructural manipulations in hiPSC-derived cortical neurons, alongside physical simulations, we establish a key ER structure-function principle: neuronal ER architecture dictates Ca2+ replenishment speed. Altering ER structure hinders network ER luminal connectivity and Ca2+ propagation from refill points at plasma membrane contact sites, impairing the ERs capability to supply repetitive Ca2+ bursts. The ER morpho-regulatory control of Ca2+ refill speed thus constitutes a switch on neuronal activity. These results expose the selective vulnerability of Ca2+-firing cells to ER structural disruptions, rationalising ER dysfunction in neurodegeneration. This mechanism could apply universally to Ca2+-firing cells.

cell biology↗

bioRxiv2023

Luminal transport rates through intact endoplasmic reticulum limit the magnitude of localized Ca2+ signals

The endoplasmic reticulum (ER) forms an interconnected network of tubules stretching throughout the cell. Understanding how ER functionality relies on its structural organization is crucial for elucidating cellular vulnerability to ER perturbations, which have been implicated in several neuronal pathologies. One of the key functions of the ER is enabling Ca2+ signalling by storing large quantities of this ion and releasing it into the cytoplasm in a spatiotemporally controlled manner. Through a combination of physical modeling and livecell imaging, we demonstrate that alterations in ER shape significantly impact its ability to support efficient local Ca2+ releases, due to hindered transport of luminal content within the ER. Our model reveals that rapid Ca2+ release necessitates mobile luminal buffer proteins with moderate binding strength, moving through a well-connected network of ER tubules. These findings provide insight into the functional advantages of normal ER architecture, emphasizing its importance as a kinetically efficient intracellular Ca2+ delivery system. Significance StatementThe peripheral endoplasmic reticulum forms a continuous network of tubules extending through the entire cell. One of the key functional roles of the ER is the release of Ca2+ ions into the cytosol to support a broad diversity of intracellular signaling processes. Such release events are enabled by the high Ca2+ storage capacity of the ER. This work demonstrates that mobile Ca2+binding buffer proteins and a well-connected lattice-like architecture of the ER network are optimal to supply local Ca2+ signals and that changes in ER structure can modulate Ca2+ release. By linking transport kinetics to Ca2+ release, we demonstrate a key functional role for the interconnected network architecture of the ER.

cell biology↗

bioRxiv2021

Endoplasmic Reticulum morphological regulation by RTN4/NOGO modulates neuronal regeneration by slowing luminal transport

Cell and tissue functions rely on an elaborate intracellular transport system responsible for distributing bioactive molecules with high spatiotemporal accuracy. The tubular network of the Endoplasmic Reticulum (ER) constitutes a system for the delivery of luminal solutes it stores, including Ca2+, across the cell periphery. The physical nature and factors underlying the ERs functioning as a fluidics system are unclear. Using an improved ER transport visualisation methodology combined with optogenetic Ca2+ dynamics imaging, we observed that ER luminal transport is modulated by natural ER tubule narrowing and dilation, directly proportional to the amount of an ER membrane morphogen, Reticulon 4 (RTN4). Consequently, the ER morphoregulatory effect of RTN4 defines ERs capacity for peripheral Ca2+ delivery and thus controls axonogenesis. Excess RTN4 limited ER luminal transport, Ca2+ release and iPSC-derived cortical neurons axonal extension, while RTN4 elimination reversed the effects. SummaryIntracellular transport through the lumen of the ER network is modulated through narrowing/dilation of ER tubules by a membrane morphogen - RTN4, a process controlling axonogenesis by limiting the delivery of ER-stored Ca2+.

cell biology↗