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SUMMARY:LMB Seminar: Cell volume and dry mass across time scales in cultur
 ed mammalian cells: from milliseconds in migrating and circulating cells t
 o homeostasis during cycles of growth and division - Matthieu Piel\, Insti
 tut Curie
DTSTART:20240205T110000Z
DTEND:20240205T120000Z
UID:TALK194971@talks.cam.ac.uk
CONTACT:Scientific Meetings Co-ordinator
DESCRIPTION:The volume and dry mass of a cell are two global quantities wh
 ich have only been recently investigated in single live cells in a quantit
 ative manner. The volume of cells is well described by the classical Pump-
 Leak Model\, based on the Van’t Hoff law\, which means that it depends o
 n the most abundant species in the cells - ions and metabolites. On the ot
 her hand\, the cell dry mass mostly consists of proteins.\n\nThe timescale
  of significant volume changes (10% or more) depends 1) on water permeatio
 n through the membrane\, which can be very fast (less than a second)\, esp
 ecially if larger pores are opened\; 2) on ion fluxes\, which is slower (m
 inutes) and 3) on import/synthesis of metabolites\, which is even slower (
 tens of minutes). Depending on the context\, different processes and times
 cales can dominate. We also observed very fast volume changes (tens of mil
 liseconds) but the mechanism remains unexplained.\n\nDry mass changes disp
 lay less timescales (if one excludes loosing significant fragments of the 
 cell) and mostly correspond to protein production on the minutes to hours 
 timescale. In proliferating cells\, dry mass increases mostly steadily at 
 the exception of a short pause during mitosis and it appears mostly indepe
 ndent of volume fluctuations that cells can display when change shape or u
 nder osmotic shocks.\n\nWhen cells undergo cycles of growth and division\,
  mass and volume need to grow\, in average\, at the same rate\, to ensure 
 density homeostasis. Several studies have shown that density is strictly c
 ontrolled in cells and display very small heterogeneity in a population of
  growing cells. Nevertheless\, there is so far no experimentally validated
  model explaining how mass and volume growth are coupled in cells.\n\nI wi
 ll present our work based on single live cell measures of dry mass and vol
 ume\, mostly focusing on two questions: 1) how dry mass density is maintai
 ned through cycles of growth and division\, and is corrected upon perturba
 tions – a phenomenon called dry mass density homeostasis. A major findin
 g is that cells possess two independent homeostatic mechanisms that togeth
 er define a target density towards which cells slowing converge. Together\
 , our experiments and model demonstrate that a dual passive and active cou
 pling between dry mass and volume growth allows correction of density fluc
 tuations and long-term maintenance of dry mass density homeostasis in a po
 pulation of proliferating mammalian cells. 2) how proliferating cells main
 tain a stable size distribution through cycles of growth and division – 
 a phenomenon called size homeostasis. The general question here is how gro
 wth speed is coupled with cell cycle timing\, so that cells born small or 
 big\, or cells growing at different speeds\, end up showing on average the
  same added volume\, leading to a stable size distribution in the populati
 on. I will present an hypothesis and some preliminary evidence for a coupl
 ing mechanism based on the physical properties of the nuclear envelope. I 
 will also rapidly discuss our work on shorter timescales for volume change
 s.
LOCATION:In person in the Max Perutz Lecture Theatre (CB2 0QH) and via Zoo
 m\, link: https://mrc-lmb-cam-ac-uk.zoom.us/j/96572384351?pwd=MkJzbE1qM2dG
 d0ZSTi9hTmV0elZ5dz09 
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