Science - USA (2020-01-17)

by inhibition of PIKfyve recovered their ability
to tubulate when exposed to hypertonic solu-
tion (movie S7) and on removal of the PIKfyve
inhibitor but failed to do so when tetrandrine
was present (fig. S9). Overexpression of TPC2
alone caused lysosomes to become more tubu-
lar, suggesting that the channel may be involved
in this process (fig. S10 and movie S8).
We propose a role for ion fluxes in the endo-
cytic pathway: Extrusion of osmotically abun-
dant ions and solutes, accompanied by water,
cause vacuolar and vesicular shrinkage leading
to crenation of the membrane, forming convex
protrusions that stabilize proteins with BAR
or similar curvature-sensing domains. These
proteins, in turn, foster tubulation and eventual
scission that is critical for interorganellar traffic.
In macrophages that continuously survey the
extracellular space, an ongoing ion efflux from
the endocytic pathway drives the resolution
of fluid that is taken up during this process,
supporting recycling of receptors to maintain
their function. Thus, the resolution of organ-

elles formed during surveillance is necessary

to preserve tissue integrity.

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ACKNOWLEDGMENTS

We thank K. Aranda, Z. Liu, and M. Capurro for tissue preparation

and genotyping. We are grateful to the Transgenic and Chimeric

Mouse Core of the University of Pennsylvania for the generation

of the TPC1 line.Funding:This work was supported by grant

FDN-143202 from CIHR to S.G., the Intramural Research Program

of the NIH to R.N.G. and S.U., and by NIH grants R01 HL147379

and R01 GM133172 to D.R. C.M.B. was supported by the Wellcome

Trust Sir Henry Wellcome Postdoctoral Fellowship.Author

contributions:S.A.F. and S.G. conceptualized the project. S.A.F.,

S.U., A.S., and S.G. designed the research and wrote the paper.

S.A.F., S.U., A.S., R.F.C., C.M.B., S.M., P.B., and J.P. performed

the experiments and analyzed the results. R.N.G. and D.R.

devised the methodology, provided resources, and edited the

manuscript.Competing interests:None declared.Data and

materials availability:All data needed to evaluate the

conclusions in the paper are present in the paper or the

supplementary materials.

SUPPLEMENTARY MATERIALS

science.sciencemag.org/content/367/6475/301/suppl/DC1

Materials and Methods

Figs. S1 to S10

References ( 19 – 28 )

Movies S1 to S8

View/request a protocol for this paper fromBio-protocol.

8 February 2019; resubmitted 8 October 2019

Accepted 25 November 2019

Published online 5 December 2019

10.1126/science.aaw9544

Freemanet al.,Science 367 , 301–305 (2020) 17 January 2020 5of5

RESEARCH | REPORT