For general background, here's a link to a review from 2020. We just give a paragraph on the tiny diameter on p12. There's also more recent work from @avezovlab.bsky.social showing that tubule diameter can affect calcium diffusion, although the physiological significance in axons is unknown. Enjoy! - ThreadSky

cahirokane.bsky.social • 40 days ago

For general background, here's a link to a review from 2020. We just give a paragraph on the tiny diameter on p12. There's also more recent work from @avezovlab.bsky.social showing that tubule diameter can affect calcium diffusion, although the physiological significance in axons is unknown. Enjoy!

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madic.bsky.social•39 days ago

Thanks a lot!
So, although tubulating proteins are similar, ER diameter varies. The 25-90nm in axons still allow calcium flow, while 10-15nm in plasmodesmata do not (https://www.science.org/doi/10.1126/sciadv.abo6693).

cahirokane.bsky.social•39 days ago

Hi, thanks for the link. However, on a quick read I don't think this shows that Ca can't flow through desmotubules; rather it supports that this isn't needed for long-range Ca signalling? (P.S. also mutants that block cytosolic flow thru plasmodesmata might not block desmotubule lumen flow?)

pdchristine.bsky.social•34 days ago

Sorry to drop in, but while we indeed didn't address calcium transport through the desmotubule in that paper (our reporter was cytosolic), we did show calcium responses have dynamics consistent with diffusion on the short range scale (200 um)

cahirokane.bsky.social•34 days ago

No apologies necessary, glad to see you!

madic.bsky.social•39 days ago

True! Wouldn't know how to adress flow through DT experimentally though. Assuming its bilayers, the lumen diameter is <5nm (more like 3nm in our data) with anionic walls. Cannot imagine free diffusion through that. Maybe thats why it goes apoplasmic rout with local repeaters?

pdchristine.bsky.social•34 days ago

It has mostly been assumed that the ER is too tightly appressed to allow transport but these papers show some movement

https://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2011.04545.x

https://apsjournals.apsnet.org/doi/10.1094/MPMI-21-3-0335

cahirokane.bsky.social•34 days ago

Thanks, these look really interesting - looking forward to a closer read.

pdchristine.bsky.social•34 days ago

In response to your original question about why have continuous ER if no flow, also good to think about the desmotubule as a membrane contact site rather than a pipe connection, and the how to make a stable pore/hole if there's nothing to stop the PM closing over?

https://www.science.org/doi/10.1126/science.adn4630

madic.bsky.social•34 days ago

Thanks for the link. Their lumenal reporter protein (LRP) is 2-4nm with pI=4.3.

cahirokane.bsky.social•39 days ago

Best approach is to test actual diffusion. For Ca this is hard (but not impossible). For lumen proteins easier, e.g. FRAP-like methods. If lumen proteins can diffuse, calcium should. If they can't, calcium may or may not. And can desmotubule diameter/permeability be regulated like PD (cytosolic) is?

madic.bsky.social•35 days ago

We dont know yet. Difficult to resolve. Since curvature is believed to be maintained by reticulon/reticulon-like proteins, reducing the protein concentration should decrease curvature. Or maybe that is to simplistic?

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