| Organelle . | Is PI detected with the indicated method? . | Possible reasons for discrepancy . | ||
|---|---|---|---|---|
| . | TopFluor-PI . | PI-PLC: PI→DAG . | PI4K: PI→PI4P . | . |
| Golgi | Yes | Yes | Yes | No discrepancy |
| Lysosomes | Not tested | Yes | Trace | PI4P phosphatase (e.g., SAC2)? |
| Endosomes | Not tested | Yes | Trace | PI4P phosphatase (e.g., SAC2)? |
| Mitochondria | Yes | Yesa | Yes | No discrepancy |
| Peroxisomes | Not tested | Trace | Yes | Failure to target PI-PLC to peroxisomes? |
| ER | Yes | Trace | Yesb | Failure to target PI-PLC to ER? |
| PM | Not detected | Tracec | Not detected | PI level beneath threshold of detection? |
| Organelle . | Is PI detected with the indicated method? . | Possible reasons for discrepancy . | ||
|---|---|---|---|---|
| . | TopFluor-PI . | PI-PLC: PI→DAG . | PI4K: PI→PI4P . | . |
| Golgi | Yes | Yes | Yes | No discrepancy |
| Lysosomes | Not tested | Yes | Trace | PI4P phosphatase (e.g., SAC2)? |
| Endosomes | Not tested | Yes | Trace | PI4P phosphatase (e.g., SAC2)? |
| Mitochondria | Yes | Yesa | Yes | No discrepancy |
| Peroxisomes | Not tested | Trace | Yes | Failure to target PI-PLC to peroxisomes? |
| ER | Yes | Trace | Yesb | Failure to target PI-PLC to ER? |
| PM | Not detected | Tracec | Not detected | PI level beneath threshold of detection? |
Results were characterized as “yes” when a substantial and statistically significant signal was observed and “not detected” when a signal was neither significant nor substantial. We used “trace” to denote situations in which statistically significant but small signals (ΔF/Fpre < 10%) were observed. “Not detected” refers to situations in which no accumulation of signal was observed. Note that for TopFluor-PI, not all organelles were interrogated.
Only detected after forced targeting of PI-PLC to the mitochondrial surface.
Only detected after treatment of cells with 500 µM peroxide to inhibit endogenous PI4P phosphatase SAC1.
Only detected transiently after forced targeting of PI-PLC to the PM with a DAG sensor, and inferred by accumulation of DAG-regulated PI/PA transfer protein Nir2.