Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2024.11.05.622032

A green lifetime biosensor for calcium that remains bright over its full dynamic range

van der Linden, F. H.·Thornquist, S. C.·ter Beek, R. M.·Huijts, J. Y.·Hink, M. A.·Gadella, T. W. J.·Maimon, G.·Goedhart, J.
View original source ↗Export metadata ↓

Abstract

Fluorescent biosensors toggle between two states and for the vast majority of biosensors one state is bright and the other state is dim. As a consequence, there is a substantial difference in the signal-to-noise ratio (SNR) for the two states. The dim state has a low signal-to-noise ratio, which is problematic when precise, quantitative measurements are needed. During the engineering of a red-shifted variant of an mTurquoise-based calcium sensor, we serendipitously generated a green-emitting sensor that shows high brightness in both the calcium-bound and -unbound state, while still showing a calcium dependent lifetime change of >1 nanosecond. This sensor, named G-Ca-FLITS, is comparable in brightness to the bright state of GCaMP3 and jGCaMP7c in mammalian cells. The calcium induced loss in fluorescence intensity is only around 30% and therefore we observe little variation in the SNR when calcium levels change. G-Ca-FLITS shows negligible sensitivity to pH in the physiological range, like its turquoise parent. Using fluorescence lifetime imaging (FLIM), we measured the calcium concentration with G-Ca-FLITS in various organelles and observed in HeLa cells transient and spatially heterogeneous calcium elevations in mitochondria. Finally, we evaluated the use of G-Ca-FLITS and its turquoise predecessor for two-photon FLIM in Drosophila brains. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=120 SRC="FIGDIR/small/622032v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@1caf016org.highwire.dtl.DTLVardef@586996org.highwire.dtl.DTLVardef@7c15cdorg.highwire.dtl.DTLVardef@7b6f03_HPS_FORMAT_FIGEXP M_FIG C_FIG

Source connections

Explore related subjects

cell biologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

van der Linden, F. H., Thornquist, S. C., ter Beek, R. M., Huijts, J. Y., Hink, M. A., Gadella, T. W. J., Maimon, G., Goedhart, J.. 2024-11-06. A green lifetime biosensor for calcium that remains bright over its full dynamic range. https://doi.org/10.1101/2024.11.05.622032

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

OPN3 mediates retinal-dependent lipofuscin accumulation and its loss sensitizes keratinocytes to blue-light-induced proteomic remodeling

Lipofuscin is a blue-light-absorbing pigment that contributes to oxidative damage. Whether all-trans retinal (atRAL) contributes to its formation in response to light remains unclear. We asked whether blue-light photosensitization of atRAL promotes lipofuscin accumulation in human keratinocytes and whether this depends on Opsin 3 (OPN3). Blue-light excitation of atRAL reduced mitochondrial and lysosomal viability, impaired autophagic flux, and increased lipofuscin. OPN3 knockdown significantly reduced this accumulation. Label-free data-independent acquisition (DIA) proteomics showed that OPN3 acts at three levels. In the dark, OPN3 loss altered proteome networks associated with autophagy, apoptosis, and interferon-related responses. Under blue light, control cells activated a stress-adaptive program spanning inflammatory regulation, lipid metabolism, and mitochondrial function, which atRAL strongly amplified. This molecular signature, including induction of cellular respiration and ATP-production proteins, was largely absent when OPN3 was silenced. Respirometry showed that blue light suppressed oxygen consumption in both lines over the first 24 h, but a faster recovery in OPN3 knockdown cells at 48 and 72 h was observed. Together, these data define three functions of OPN3: maintaining the basal proteome in a blue-light-independent manner, enabling the adaptive blue-light response, and enabling retinal-dependent lipofuscin formation in keratinocytes.

cell biology↗
bioRxiv2026

Uncoupling microtubule lifetime, stability and post-translational modifications.

Microtubules (MTs) undergo continuous cycles of growth and disassembly. Because the transitions between these states are stochastic, MT age varies widely within a population. As MTs age, they are thought to accumulate post-translational modifications (PTMs) that, directly or indirectly, enhance their stability and thereby extend their lifetime. The rare MTs that withstand prolonged exposure to destabilizing drugs such as nocodazole (NZ) are indeed enriched in PTMs; yet the relationships between MT age, PTMs and stability remain unclear. Using microinjection of labelled tubulin, we measured microtubule network turnover in immortalized mouse embryonic fibroblasts. Half of the network was renewed within 3 minutes and 80% within 10 minutes, while approximately 5% of microtubules persisted for more than 20 minutes. These dynamics were comparable in quiescent and senescent cells, although the fraction of slowly renewing or non-renewing microtubules rose to 20% in senescent cells. Unexpectedly, neither the amount of PTMs (acetylation and detyrosination) nor resistance to NZ increased with MT age, and resistance to NZ was independent of these PTMs. Degrees of acetylation and detyrosination should therefore not be taken as readouts of MT age or stability. Because these PTMs do not accumulate on MTs over time, the chemical modification of polymerized tubulin is likely more reversible and dynamic than previously assumed.

cell biology↗
bioRxiv2026

Evidence of complete myofibril remodeling after severe damage in adult Drosophila.

Muscle function depends on the ability of myofibrils to withstand and repair mechanical damage, yet how adult muscles remodel damaged myofibrils remains poorly understood. Here, we establish a Drosophila model that allows the induction and longitudinal visualization of extensive myofibril damage and recovery in intact adult femur muscles. Sustained muscle depolarization caused extensive disruption of myofibrillar organization, with severe damage characterized by near-complete loss of Z-disc structures. Remarkably, myofibril architecture and muscle function were largely restored within days, revealing a substantial capacity for myofibril reconstruction in adult femur muscles. We identified two distinct states of myofibril damage, mild and severe, with mild damage appearing before severe damage during aging, suggesting a progressive process of myofibril deterioration and repair failure. We further show that filamins mechanosignaling is required for efficient myofibril remodeling. Following damage, wild-type filamin redistributes from the Z-disc and accumulates outside the myofibrils, whereas constitutively open filamin remains Z-disc-associated and constitutively closed filamin redistributes but results in increased damage and impaired recovery. These findings suggest that effective repair requires dynamic transitions between filamin conformational states and that filamin redistribution is an active component of the damage response rather than simply a consequence of muscle injury. During aging, filamin progressively redistributes from the Z-disc and muscle damage accumulates, with severe damage increasing after the appearance of mild damage. Together, our findings reveal a previously unappreciated capacity of adult muscle to reassemble damaged myofibrils and identify filamin mechanosignaling as a key component of this repair process, providing a framework for understanding how defective mechanosensing may contribute to age-related muscle decline and muscle disease.

cell biology↗