Lysosome enlargement in PIKfyve inhibited cells proceeds through homotypic lysosome fusion rather than growth of individual lysosomes
Bibliographic record
Abstract
Phosphoinositides are important lipids that modulate various functions including signal transduction, membrane trafficking, and organelle identity. Phosphatidylinositol‐3,5‐bisphosphate [PI(3,5)P 2 ] is a phosphoinositide found on lysosomes where it controls a wide array of functions such as stress‐induced signalling, autophagic flux, ion‐channel activity, trafficking and endolysosome morphology. Lysosomes are degradative organelles where macromolecules, foreign pathogens, and intracellular organelles arrive through endocytosis, phagocytosis and autophagy for degradation, respectively. PI(3,5)P 2 is synthesized from phosphatidylinositol‐3‐phosphate [PI(3)P] via the lipid kinase PIKfyve. One of the most dramatic phenotypes in cells deficient for PI(3,5)P 2 synthesis is the enlargement of lysosomes. However, the dynamics and mechanism of lysosome enlargement due to PIKfyve inhibition remains mostly unexplored. We aimed to distinguish whether lysosome swelling proceeds through growth of individual lysosomes or if multiple lysosomes fuse together culminating in enlarged lysosomes in cells treated with apilimod, a specific inhibitor of PIKfyve. Using a combination of spinning disc microscopy and volumetric/particle counting analysis, we show that lysosome enlargement in PIKfyve‐inhibited cells results from homotypic lysosome fusion rather than by growth of individual lysosomes. This is supported by a decrease in lysosome number and increase in volume of individual lysosomes, while total lysosome volume remained constant. These effects are reversed upon washing of apilimod. Consistent with this, disruption of microtubules and microtubule‐associated motor complexes, dynein and kinesin‐1, reduced the rate of lysosome enlargement in PIKfyve‐inhibited cells, while accelerating shrinkage of lysosomes during apilimod removal. We propose a model whereby lysosomes undergo constant kiss‐and‐run (fusion and fission) events. In the absence of PIKfyve, lysosomes “kiss” but fail to “run”, leading to a shift towards homotypic fusion, which increases the size of individual lysosomes and a reduction in total lysosome number. Support or Funding Information This work was made possible by NSERC and Canada Research Chair Program.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".