Cellular Growth and Form - Course 1: From tissues to cells: size and complexity Thomas Lecuit - Collège de France
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Cellular Growth and Form
Course 1: From tissues to cells: size and complexity
Thomas Lecuit
chaire: Dynamiques du vivant
1How to account for the extraordinary diversity of shapes?
ppinterest.com
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PLANCTON Aux origines du vivant, Editions Ulmer, octobre 2013, Christian Sardet
Thomas LECUIT 2020-2021In search of the principles of biological shapes…
«Le savant doit ordonner;
on fait la Science avec des faits comme une
maison avec des pierres ;
mais une accumulation de faits n'est pas plus
une science qu'un tas de pierres n'est une
maison.»
Henri Poincaré (1854-1912)
La science et l’hypothèse (1902)
«La Science remplace du visible compliqué
par de l'invisible simple. »
Jean Perrin (1870-1946)
Thomas LECUIT 2020-2021
3Plasticity and constraints in morphogenesis
Tissue shape: 2017 and 2018
Tissue size: 2019
• Variation in shapes • Variation in size:
Size Shape
(6 orders of magnitude in Metazoa)
Amoeba proteus
1 mm Escherichia coli
1 μm
100 μm
10 μm
10 mm Paedophryne Megaphragma
amauensis mymaripenne
1 mm
10 cm 100 cm
Lecuit T. and Le Goff L. Nature. 2007 ;450(7167):189-92. doi: 10.1038/nature06304.
10 m
Goliathus
•
cacicus
Multicellularity: diversification Blue whale
1m
of cell types, modularity of
developing shapes.
100 m
Thomas LECUIT 2020-2021
4Plasticity and constraints in morphogenesis
40 My 60-65 My
• Evolutionary radiation with
extensive or limited shape
variation
Drosophilidae
Membracidae
Nicolas Gompel (LMU Munich)
granivores
scaling shear
Tiaris bicolor
Geospiza fuliginosa
• Internal constraints: Geospiza magnirostris Geospiza fortis
Geospiza fortis
depth
— historical, genetic (networks),
Galapagos Islands Geospiza magnirostris
Pinta
group 1 length
Genovesa
Geospiza scandens
functional and physical. Fernandina
Santiago
Pinzón
Baltra
Geospiza conirostris
Geospiza difficilis
Santa Cruz
San Cristóbal
Camarhynchus parvulus
Isabela
Floreana
Camarhynchus psittacula
Camarhynchus pallida group 2 parabola
0 = Ax2 + Bxy + Cy2 + Dx + Ey
Pinaroloxias inornata
Certhidea olivacea
Geospiza parvula Certhidea olivacea Platyspiza crassirostris group 3
insectivores
O. Campas et al. and A. Abzhanov, M. Brenner. PNAS (2010)∣ 107:3356–3360
Thomas LECUIT 2020-2021
5Plasticity and constraints in morphogenesis
10 h TP1
18 h TP2
maternal Otx ßCat Ets1 Notch SoxB1 GCad
zygotic Mif7 Dkk RBM8A
ßCat Tcf GSK3 Frzld 24 h TP3 2
redox gradient
development
Apical_E/M
Otx Blimp1 Wnt8 ActvB RhoA SoxB1 Nodal Lefty Hnf6
28 h TP4
dimensionality
Pmar HesC Hnf6 ES SoxC Otx Blimp1 Wnt8 HesC Gsc FoxG Chordin
1
Alx1 Ets1 TBr Delta Nrl SuH FoxA Hox11/13 Eve Sip1 Otx BMP2/4
reduction 38 h TP5
Tel Erg Hex Tgif FoxN2/3 Notch Delta GataE Nrl Dri
Mitf Dri FoxB FoxO VEGFR Tgif Gcm Bra Not Bra Hes
1
/A
VegF Brn124 Hnf6 Alx1 Nk1 Lim1 0.5
ec 5
_L
SM27 SM50 Msp130 Msp-L C-lectin
0.06
3
45 h TP6
0.
to
Hex Snail GataC Fmo1,2,3 Tbx2.3 IrxA Dlx
SM30-E GCad Ficolin CyP 0.35
06
SM32 CollA P16 P19 Kakapo Endo16 Apobec Gelsolin Lhx2.9 Nkx2.2 Hmx
0.
Endo_ 1
es
skeletogenic endomesoderm ectoderm 90 h TP7 L/A
M
Sherrard K et al Current Biology 20, 1499–1510
Garfield DA et al. PLoS Biol 11(10): e1001696. (2013) doi:10.1371/journal.pbio.1001696
Genospace Morphospace
much, much lower dimensional space
>15.000 genes
10 functional alleles per gene?
• viability/functional fitness
dimension: 1015000 !!!
• constraints: historical, physical etc
• few effective parameters
See also, for a discussion: Ard A. Louis. Studies in History and Philosophy of Biological and Biomedical Sciences 58 (2016)
Contingency, convergence and hyper-astronomical numbers in biological evolution
Thomas LECUIT 2020-2021
6 44 !%+
&%+)"%+ * +'#*+" "+4, &,)* , 4- #&'' $ %+ + #84-&#,+"&%
Constraints and plasticity in Development and Evolution
- %"*,&,# !") 2-&#,+"&% * 4%&$ * + 4- #&'' $ %+
3-4 Juin 2021 — 9h-18h
"1. % $4 ""/" %44$*37/6
$98$" %"4'#
Detlev Arendt (EMBL Heidelberg)
Virginie Courtier-Orgogozo (Paris)
Stanislas Dehaene (Collège de France)
Claude Desplan (NYU)
Organisateurs: Caroline Dean (John Innes Center)
Denis Duboule (chaire: Evolution des Liam Dolan (Oxford)
Hopi Hoekstra (Harvard)
génomes et développement)
Laurent Keller (Univ. Lausanne)
Thomas Lecuit (chaire: Dynamiques du Natacha Kurpios (Cornell Ithaca)
vivant) Shigeru Kuratani (Kobe)
L. Mahadevan (Harvard)
Marie Manceau (Collège de France)
Nipam Patel (Woods Hole)
Olivier Pourquié (Harvard)
Luis Quitana-Murci (Pasteur & Collège de France)
Eric Siggia (Rockefeller University)
Vikas Tervidi (EMBL Barcelona)
Elly Tanaka (IMP Vienna)
Günter Wagner (Yale Univ.)
7Plan
Course 1: From tissues to cells: size and complexity
1. Universal classes of tissue shapes
2. Impact of multicellularity in shape space
—Is multicellularity required for tissue shape?
3. Complexity of unicellular organisms
—Large single cells can «behave» like
multicellular organisms
—From the most complex unicellulars to the
most simple multicellulars
Thomas LECUIT 2020-2021
8Universal classes of Shapes
All forms arise from few «elementary shape transitions»
operating across scales
Spatial and temporal combination of such operations
Folding
Thomas LECUIT 2020-2021
9Universal classes of Shapes
All forms arise from few «elementary shape changes» across scales
Spatial and temporal combination of shape changes
EXTENDING
LOOPING/COILING
(A) (B) (C)
BRANCHING
GEOMETRY CHANGE
(A) (C) (E)
INVAGINATING
5 μm 20 μm 500 μm
(D) (E) 2 mm
(D)
2 mm
(F)
CAVITIZING 5 μm
(B)
TOPOLOGY CHANGE
1 mm 100 μm ??? ???
200 μm ???
Bending, Folding, Looping
Branching
Thomas LECUIT 2020-2021
10Universal classes of Shapes
Arise from basic physical principles
•(near) Equilibrium shapes:
— surface tension: minimal surfaces
Gtot = γ •A γ = ƒ(cortical tension, adhesion)
limb bud 0.02 N/m
pigmented 0.01 N/m
epithelium
heart 0.008 N/m
liver 0.005 N/m
neural
M. Steinberg et al
retina 0.002 N/m
Thomas LECUIT 2020-2021
11Universal classes of Shapes
Arise from basic physical principles
• (near) Equilibrium shapes:
— elasticity: buckling
ds dA
R1
R bending the mesentery sheet
R2
area of
(C)
Young areal bending deformed sheet
×
STIFFNESS
modulus moment stiffness
Estretch = EmЄ2 h λ2
thickness of
E I Kbend λ sheet
bending the gut tube
λ
(D) 3 cm
DEFORMATION
1 1 1
+
R R1 R2
d λ
radius of radius of curvature
curvature in orthogonal length of segment
directions EI 1
2 mm
Ebend ≈ λ
2 λ2
L 2 Kbend 2
ENERGY
1 1 1
∫ ∫
EI curvature
ds dA +
2 0
R(s) 2 R1 R2
from Rob Phillips (CalTech) and Christina Hueschen (Stanford Univ.)
after Thierry Savin, et al, L. Mahadevan and Cliff Tabin. Nature (2011) 476:57-62.
Thomas LECUIT 2020-2021
12Universal classes of Shapes
Arise from basic physical principles
• Dynamic steady-state shapes: —Aggregation
-activity driven self-organisation (A) (C)
traction
elasticity
one many none
—Flow, pulses, waves of contraction
(B)
45.8 kPa 6.12 kPa control 0.418 kPa 0.195 kPa 0.025 kPa
pattern geometry
500
400
300
zoom 200
elasticity 500 μm 100
0
.8
co .12
0. l
0. 8
0. 5
5
ro
41
19
02
45
nt
6
(kPa)
elasticity
cross section DAPI
100 μm
force balance
∇ σviscous + σelastic + σtraction = 0
after Shyer et al. Science 357, 811-815 (2017)
Wave of tissue folding (Drosophila embryo)
Bailles and Collinet et al. Nature 572, 467-473 (2019)
Thomas LECUIT 2020-2021
13Origin of tissue and organism shape diversity
• Developmental Modularity: metamers (segments) and tagma
• Modular control of size and shape in each segment: morphological diversification
head
thorax
abdomen
Pycnogonida
Drosophila melanogaster
Marrella (Burgess Shale) Buthus occitanus Scutigera forceps Crayfish
500 Mya
https://www.alamy.fr/
Thomas LECUIT 2020-2021 https://www.gutenberg.org/
14Origin of tissue and organism shape diversity
• Modularity: metamers (segments) and tagma
• Modular genetic control of shape
Bcd,
Lab Pb Zen Dfd Scr (Ftz) Antp Ubx AbdA AbdB
Drosophila
Hox complex
anterior posterior
Hox1 Hox2 Hox3 Hox4 Hox5 Hox6 (central) Hox7 (posterior)
ancestral
Hox complex
spinal cord mammalian
hindbrain Hox complex A1 A2 A3 A4 A5 A6 A7 A9 A10 A11 A13
HoxA
anterior posterior B1 B2 B3 B4 B5 B6 B7 B8 B9 B13
HoxB
C4 C5 C6 C8 C9 C10 C11 C12 C13
HoxC
D1 D3 D4 D8 D9 D10 D11 D12 D13
mesoderm HoxD
Ed Lewis, C. Nüsslein-Volhard and E. Wieschaus (Nobel 1995)
Denis Duboule and many other groups
Rob Philipps, Jane Kondev, Julie Theriot, Hernan G. Garcia.
Thomas LECUIT 2020-2021 Physical Biological of the Cell (Garland Science)
15Plan
Course 1: From tissues to cells: size and complexity
1. Universal classes of tissue shapes
2. Impact of multicellularity in shape space
—Is multicellularity required for tissue shape?
3. Complexity of unicellular organisms
—Large single cells can «behave» like
multicellular organisms
—From the most complex unicellulars to the
most simple multicellulars
Thomas LECUIT 2020-2021
16Impact of multicellularity on the morphospace
• Multicellularity occurred in at least 16
independent eukaryotic lineages
• Multicellularity allowed:
1) escape from predation
2) solution to motility/division
antagonism (centriole
required for both
ciliogenesis and formation
of mitotic spindle)
3) exploration of new
differentiated cell functions
• Molecular data support monophyletic
origin of all Metazoa, including Porifera
(sponges)
Thomas LECUIT 2020-2021
17Impact of multicellularity on the morphospace
• Choanoflagelates are aquatic protozoans that share many features with
animals, and thus are considered the closest unicellular relatives of animals
• Facultative multicellular (colonial) states in Choanoflagelates
(A) (B)
cell
ECM
5 m
Salpingoeca rosetta
(C)
King N. Developmental Cell 2004
Thomas LECUIT 2020-2021
18Impact of multicellularity on the morphospace
Saville-Kent explored the great diversity of Infusoria (Choanoflagelates)
William Saville-Kent
(1865-1908)
Manual of the Infusoria 1880-1882
Thomas LECUIT 2020-2021
19Impact of multicellularity on the morphospace
(A)
1.0
scaled ECM stiffness
d1 t1
0.8 rosettes
•
r1
Morphogenesis of cell aggregates
0.6 disks
(ı)
0.4 cups and cones
•
c2
Mechanical model of self-assembly 0.2 d
0.9
2 c3
trees
of cell aggregates.
c1 0.14
0.8
cell 0.7
0.6 0.06 0.10 e
asp 0.02 volum
•
ect 0.5
3 effective parameters can change (Į ) ratio e ECM
relativ (ĭ)
outcome of cell interactions and 0.9
ı= 0.6
1.0
Į= 0.8
1.0
ĭ= 0.04
shape 0.8 0.8 0.8
• Adhesion/cell coupling via the ECM 0.6 0.6
ı
ı
0.7
Į
•
0.4 0.4
Geometric parameter: aspect ratio
0.6
0.2 0.2
0.5
0.02 0.06 0.10 0.14 0.02 0.06 0.10 0.14 0.5 0.6 0.7 0.8 0.9
ĭ ĭ Į
(B)
rosette disk disk cup cone cup tree
r1 d1 d2 c1 c2 c3 t1
cell
Cell ECM
90° 90° 90° 90° 90° 90° 90°
ECM
• Cell aggregates can (model) and rosettes disks cups and cones trees
do (experiments) form rosettes, r2 d3 c4 t2
disks, cups, cones or trees
r3 d4 c5 t3
Thomas LECUIT 2020-2021 10 m 10 m 10 m 10 m
20 Ben Larson et al, L Mahadevan and N. King (2019) www.pnas.org/cgi/doi/10.1073/pnas.1909447117Impact of multicellularity on the morphospace
• Ligth induced morphological change in colony of Choanoflagelate (Choanoeca flexa)
(A) (C) LIGHT
apical relaxed form (flagella in) 0s
flagellum
feeding
collar
cell body
basal bacteria 3s
4 m
(B) darkness
light
rhodopsin
6s
flow
N retinal
PDE DARK Choanoeca flexa
inverted form (flagella out) 10 m
cGMP
swimming
C
5ƍ GMP
inversion
T. Brunet et al., and N. King. Science 366, 326–334 (2019)
Thomas LECUIT 2020-2021
21Impact of multicellularity on the morphospace
• Collective contractility drives colony shape changes
(A) (B) (C)
collar
myosin II light on light off closure
F-actin ring
1.0
normalized sheet area
ring 0.8
ring contraction ring relaxation
collar opening
0.1% DMSO
0.6 (negative control)
ring 2 M latrunculin B
2 M blebbistatin
2.2 M ML-7
0.4
–20 –15 –5 5 15 25
5 m 2 m time (s)
Thomas LECUIT 2020-2021 T. Brunet et al., and N. King. Science 366, 326–334 (2019)
22Impact of multicellularity on the morphospace
• Suggests that collective cell dynamics is required for emergence of complex
shapes such as invagination.
• Such collective cell dynamics rests on a limited set of cellular processes such
as contractility and cell-cell coupling
T. Brunet et al., and N. King. Science 366, 326–334 (2019)
Thomas LECUIT 2020-2021Tissue shape: is multicellularity required?
— Drosophila embryo gastrulation without cells
Syncytial divisions
1 cell : 1 nucleus
1 cell : 5000 nuclei
Cellularisation: 5000 cells
Membrane invagination leads to the Patrick Keller — Janelia Farm
formation of many cells at once
Thomas LECUIT 2020-2021
24Tissue shape: is multicellularity required?
— Drosophila embryo gastrulation without cells
• Bulk cytoplasmic flow in the ventral mesoderm is associated with
tissue invagination
• Bulk flow is similar to predicted Stokes flow given known boundary
conditions (active cortical flow driven by actomyosin contractility)
• Suggests that tissue behaves as a homogenous fluid (cytoplasm)
active cortical flow bulk cytoplasmic flow
apical wild type
0
20
AB (μm)
basal
40
yolk
60
3μm min–1
80
–80 –40 0 40 80
measurements μm μm
minML
–1 (μm) min–1
0 4 0 4
Vx 3
Vy
3
20 2 20
1 2
40 0 40 1
–1 0
–2
60 –3
60 –1
–4 –2
80 80
–80 –40 0 40 80 –80 –40 0 40 80
predicted Stokes flow μm μm
min–1 min–1
10 V 4 10 V 4
x 2 y
2
30 0 30 0
–2
50 –4 50 –2
–80 –40 0 40 80 –80 –40 0 40 80
Thomas LECUIT 2020-2021
25 He et al. and E. Wieschaus. Nature (2014) 508:392-396Tissue shape: is multicellularity required?
— Drosophila embryo gastrulation without cells
d Wild type
Acellular
• In an acellular embryo (syncytium)
Junction Membrane
bulk cytoplasmic flow still occurs
• Acellular flow is similar to
predicted Stokes flow, and also wild type acellular
similar to flow in cellularized tissue 0 0
20 20
AB (μm)
AB (μm)
40 40
60 60
3μm min–1 2μm min–1
80 80
–80 –40 0 40 80 –80 –40 0 40 80
•
ML (μm) ML (μm)
«tissue» furrowing occurs (albeit
more slowly) in acellular embryo.
angle of furrow (degrees)
60 Measurement versus theory
wild type
acellular 10
40
30
20
θ 50
0 –80 –40 0 40 80
–20
0 2.5 5 7.5 10 12.5
0 4 8 12 16 20
time (min)
He et al. and E. Wieschaus. Nature (2014) 508:392-396
Thomas LECUIT 2020-2021
26Tissue shape: is multicellularity required?
— Drosophila embryo gastrulation without cells
• Cortical flow can be predicted from pattern of MyosinII and geometry.
• Flow still occurs in acellular embryo
Lye CM, et al , and B. Sanson. (2015) PLoS Biol 13(11): e1002292. doi:10.1371/journal. pbio.1002292
See also:
Dicko M, Saramito P, Blanchard GB, Lye CM, Sanson B, Étienne J. PLoS Comput Biol. 2017 Mar 27;13(3):e1005443.
Streichan S. et al eLife. 2017
Thomas LECUIT 2020-2021
27Tissue shape: is multicellularity required?
— Tubulogenesis in Salamanders:
Morphogenesis is independent of cell size and cell number.
• Cell size compensates for change in cell number
• A single cell forms a lumen
(A) (C) larvae
haploid (n) diploid (2n) pentaploid (5n)
(B)
diploid (2n) pentaploid (5n)
pronephric tubules
Fankhauser G. 1945. J Exp Zool 100: 445–455.
Thomas LECUIT 2020-2021
28Tissue shape: is multicellularity required?
— Mouse embryo lumenisation without cells?
• Formation of the blastocoel in mouse embryos occurs in non-muscle
Myosin-II heavy chain mutants that block cytokinesis
• This leads to the formation of intracellular lumenisation and growth of a
vacuole
M.F. Schliffka et al, and J-L. Maître.
bioRxiv https://doi.org/10.1101/2020.09.10.291997
mzMyh9+/-;mzMyh10+/- embryo
Thomas LECUIT 2020-2021
29Tissue shape: is multicellularity required?
— Physarum polycephalum: an acellular self-organised optimal transport system
• A plasmodial myxomycete (Protist, Amoebozoa)
• Contains 1000s to millions of nuclei in a syncytium called plasmodium
• Grows towards food source
• Self-organizes a hydrodynamic network to distribute food to the entire cell/organism
1 cm/hr
Heather Barnett
Life cycle
Thomas LECUIT 2020-2021
30Tissue shape: is multicellularity required?
— Physarum polycephalum: an acellular self-organised optimal transport system
• Self-organisation of network morphology
• Phase gradient of contraction across network
• Peristaltic wave drives long-range cytoplasmic flow in the plasmodium
(b) (c) 2p
3p/2
p
p/2
500 μm 0
2000 μm
Alim K. 2018 Fluid flows shaping organism morphology.
Phil. Trans. R. Soc. B 373: 20170112. http://dx.doi.org/10.1098/rstb.2017.0112
100 μm
Thomas LECUIT 2020-2021
31Tissue shape: is multicellularity required?
• Obviously yes, But:
• No, to a certain extent:
• It reflects the amazing self-organising properties of intracellular material
(non genetic, non deterministic information).
—Compartmentation in absence of
membranes
—Cell-like units can divide
(a sperm-supplemented cycling X. laevis egg extract)
Spontaneous emergence of cell-like organization in
Xenopus egg extracts
Xianrui Cheng1* and James E. Ferrell Jr.1,2*
Thomas LECUIT 2020-2021 Cheng et al., Science 366, 631–637 (2019)
32Tissue shape: is multicellularity required?
• Obviously yes, But:
• No, to a certain extent:
• It reflects the self-organising properties of intracellular material
(non genetic, non deterministic information).
• The efficacy of continuum physical models is a consistent with this:
In such coarsed-grained descriptions, cell individuality is lost and tissues are
described as a continuous medium driven by active mechano-chemical
processes.
Elasticity theory, Active matter theory etc.
• Especially in large cells (or acellular tissues).
• Large single cells can behave like multicellular organisms
Thomas LECUIT 2020-2021
33Plan
Course 1: From tissues to cells: size and complexity
1. Universal classes of tissue shapes
2. Impact of multicellularity in shape space
—Is multicellularity required for tissue shape?
3. Complexity of unicellular organisms
—Large single cells can «behave» like
multicellular organisms
—From the most complex unicellulars to the
most simple multicellulars
Thomas LECUIT 2020-2021
34Size and complexity
• Large single cells can behave like multicellular organisms
Paramecium caudatum
Megaphragma mymaripenne
7500 cells in brain
Motility
Feeding
Amoeba proteus
Environment sensing
200 μm
Alexey Polilov. Arthropod Structure & Development 41 (2012) 29e34
Thomas LECUIT 2019-2020
35Size and complexity: « single cell organisms »
• Pure self-organisation of single cell • Genetic determination of 5000 cells
https://sguenther.eu/data/life-in-perspective/fruit-fly-embryo/
5000 cells
10-100 fates
1 cell 1 fate
Thomas LECUIT 2020-2021
36Size and complexity: single cell organisms
• Multicellular tissue dynamics • Giant cell dynamics
Trichoplax adhaerens motility Amoeba proteus motility
200μm
Several 1000 cells 1 cell
(from Manu Prakash, Stanford Univ.)
Thomas LECUIT 2020-2021
37Size and complexity: « single cell organisms »
rosophila ggastrulation
Drosophila
D astrulation
• Multicellular tissue dynamics
Drosophila melanogaster embryo
• Giant cell dynamics
Megaphragma mymaripenne
Spirostomum ambiguum
Ciliate
Thomas LECUIT 2020-2021
38Unicellulars versus Multicellulars
• Unicellular organisms contribute approximately ⅔
of the total biomass of marine organisms
(protists and bacteria) and 10% of land organisms.
• Protists (non animals/plants/fungi, 30% of
biomass), are mostly unicellular non-
photosynthetic eukaryotes, and photosynthetic
algae.
• Biomass of marine and land protists is 3 times the
biomass of all land animals!
A B
Y. Bar-On and Ron Milo Cell 179:1451
Y Bar-On, Rob Phillips and Ron Milo PNAS 115: 6506–6511
Thomas LECUIT 2020-2021
39Unicellulars versus Multicellulars
• Complex Organisation
(ie. differentiated cell)
• Division
• Regeneration
• Motility
• Behaviour: food uptake, attack/killing
• Cooperative behaviours
(in some cases)
Thomas LECUIT 2020-2021
40Complexity of unicellulars
• Division of cells in spite of complex organisation
• In multicellular organisms, complex cells (ie. differenciated cells) are non mitotic
(the absence of cell division relaxed a contraint on cell complexity and allowed
increase in cell size with complex shapes)
100μm
Green alga — Micrasterias rotata
10 μm
https://www.pinterest.fr/pin/174373816795440020/
Thomas LECUIT 2020-2021 Podocyte
41Complexity of unicellulars
• Stentor coeruleus: Complex organisation of a Ciliate
Vance Tartar 1911-1991
Thomas LECUIT 2020-2021
42Complexity of unicellulars
• Regeneration: Stentor coeruleus (Ciliate)
1960
1901
Thomas H. Morgan
1866-1945
Biological Bulletin , Jun., 1901, Vol. 2, No. 6 (Jun., 1901), pp. 311-328
Thomas LECUIT 2020-2021
43Complexity of unicellulars
• Behaviour - Predation: Stentor coeruleus (Ciliate)
direction of metachronal wave
cilium
membranelle
membranellar
band
moniliform
macronucleus
oral pouch/ intermembranellar
gullet region connections
basal
bodies
locus of stripe
contrast
holdfast ciliary roots
basal fibre
0 mm s–1 50 100 150
(b)
control
K. Wan et al, and W. Marshall
https://www.youtube.com/watch?v=PZoaKzEXzi8&t=86s
Philos Trans R Soc Lond B Biol Sci
. 2020 Feb 17;375(1792):20190167.
Thomas LECUIT 2020-2021
44Complexity of unicellulars
• Behaviour - Predation: Lacrymaria olor (Ciliate)
helical
• Lacrymaria is a unicellular cytoskeleton
predator that hunts using
extreme morphology retracted
dynamics !!!!
captured
50μm
•
prey
Morphology dynamics result in
dense stochastic sampling of extended
the local environment
• Behavior emerges from fast
prey
and slow response of helical
cytoskeleton to cyclic stress
fast slow emergent cellular
dynamics + plasma microtubules
dynamics hunting behavior membrane
seconds minutes
cytoplasm
centrin
probability
low high
Coyle et al., 2019, Current Biology 29, 3838–3850 November 18, 2019
https://doi.org/10.1016/j.cub.2019.09.034
Thomas LECUIT 2020-2021
45Complexity of unicellulars
• Behaviour - Collective protection: Spirostomum
• One of the largest Ciliates (up to 2 mm long) undergoes ultra fast contraction
Mi Ma Fv Ex Ci Cs Sg
1 mm
Rapid Slow
contraction relaxation 200
Acceleration (m s–2)
100
0
–100
100 μm
Start –200
–2.5 0 2.5 5 20 250 350 600 ms –10 0 10 20
Time (ms)
Spirostomum ambiguum
Ca2+ channels Ca2+ pumps
Myonemes Microtubules
Fluid dissipation
A. JTM. Mathijssen et al. and M. Prakash. Nature. 2019 Jul;571(7766):560-564.
doi: 10.1038/s41586-019-1387-9
Thomas LECUIT 2020-2021
46Complexity of unicellulars
• Behaviour - Collective protection: Spirostomum
— At rest, metachronal waves of cilia cause fluid flow
— Ultrafast contraction causes inertial flow
Spirostomum ambiguum
c PIV experiment d PTV experiment
LNS theory Simulated tracers
0 6 mm s–1 ||v|| 0 20 ms
200 200
e 1.0
Fluid inertia f
1.0 0.8 High viscosity
0.6
v/vmax
0.8
0.4
0.2
0.6
v/vmax
0
–5 0 5 10 15 20 25 30
0.4 Time (ms)
0.2 Low viscosity
0
–5 0 5 10 15 20 25 30
Time (ms)
Organism Water 3% MC
A. JTM. Mathijssen et al. and M. Prakash. Nature. 2019 Jul;571(7766):560-564.
doi: 10.1038/s41586-019-1387-9
Thomas LECUIT 2020-2021
47Complexity of unicellulars
• Behaviour - Collective protection: Spirostomum
a
b 2 mm
— A gradient of flow causes a
Flow strength vf ( U)
gradient of membrane tension U
at the cell surface
—This elicits opening of gated c mN m–1
0 0.3
mechanosensitive calcium 2×
channels and cell contraction
—The critical strain rate
decreases with cell size: large mN m–1
cells are more d 1.0
e 0.07 0.34
mechanosensitive
Cumulative probability
Critical strain rate (1/s)
0.8
0.6
mN m–1
200
Critical strain rate (1/s)
0.4 0.07 0.34
150
0.2
100
0
0 0.1 0.2 0.3 0.4
50
Membrane tension (mN m–1) P = 1.9 × 10–12
r = –0.950
0
0.4 0.6 0.8 1.0
Organism length (mm)
A. JTM. Mathijssen et al. and M. Prakash. Nature. 2019 Jul;571(7766):560-564.
doi: 10.1038/s41586-019-1387-9
Thomas LECUIT 2020-2021
48Complexity of unicellulars
• Behaviour - Collective protection: Spirostomum
— A hydrodynamic «trigger wave» propagate cell
contraction in a population of Spirostomum.
—The percolation probability depends on cell density.
c Pairwise
Pair
airwis
wise
w is
s interactions
int
n errac
ction
on
ns
a 1
M
S
1
U
T
y
1 0
–1 00 s–1
100
1
–1
–1 x (mm)
(mm
mm
m m) 1
1 mm
t=0 64 ms
f Below transition: n = 1 per
p mm2 g Near
N ear tran on: n = 2 p
transition:
an
nsit
s ion
ion:
io per m 2
er mm
er h Abo
Above
ove on: n = 3 p
e transition:
tra
ttr
rra
ansi
n tio
ns per m 2
e mm
er
b Organism density, n (no. per mm2)
0.5 1.0
Signal velocity (m s–1)
Percolation probability
0.4 0.8
I II III
0.3 0.6
0.2 0.4
0.1 0.2
F G H
0 0
5 ms
ms 4 mm 24
243
2 3 ms
s 4 mm
m 10
105
05 ms
s 4 mm
0 1 2 3 4 5
A. JTM. Mathijssen et al. and M. Prakash. Nature. 2019 Jul;571(7766):560-564.
Thomas LECUIT 2020-2021 doi: 10.1038/s41586-019-1387-9
49The most simple multicellular
Plachozoa: Trichoplax adheraens
(A) (B) (C)
— The most simple animal, a marine
organism without distinct shape 3–5 mm
—Forms a thin sheet, contains 6 cell
types only, without muscle and nerve dorsal
cell.
dorsal epithelial cell
—Trichoplax move and change shape
constantly and split.—What is the nucleus
sac
difference between large single cell ventral
and small sheet of cell?
?? μm
S. Amon et al. and M. Prakash. PNAS 115: E10333–E10341 (2018) www.pnas.org/cgi/doi/10.1073/pnas.1802934115
Thomas LECUIT 2020-2021
50The most simple multicellular
Plachozoa: Trichoplax adheraens mean
mean
intensity
[a.u.]
intensity
[a.u.]
x[mm] Tplax epithel. Embryo epithel. Cells in vitro
Area reduction rate [1/sec]
C 0s 5s D 0s 4s Sponge epithel. Molecular assays
102
order of
101 magnitude
—Ultrafast cell contraction 100
depends on MyosinII contractility 100um 35um −1
10
E 0s 3s F 3s 4.5s
−2
—Active cohesion mechanism 2 2 10
Dorsal Closure
Embryogenesis
Spontanous
Invaginaon
Axis elongaon
Osmoc shock
Gastrulaon
Gastrulaon
+ATP
Rythmic
Gohst cytokin.
MDCK monolayer
1D bundles-max
Twitch
RVD
2D bath
1D rings
1D bundles
8 8
6 6 7
ensures tissue integrity 1
7
3 11 3
5 5 4
4
20um 2um
t.
an
ge
n
M ast
Hu use
og
As lax
Fly
ns
ia
m
on
Fr
Tp
Ye
id
co
o
(A)
Sp
Re
0200 sec 0300 0350
area change rate (sec–1) 100 m
–0.5 0 0.5
(B) external forces (C) tissue under tension
locomotion
(i) simultanous softening
100μm (ii) simultanous contractions
(iii) active cohesion
contraction softening
S. Amon et al. and M. Prakash. PNAS 115: E10333–E10341 (2018) www.pnas.org/cgi/doi/10.1073/pnas.1802934115
Thomas LECUIT 2020-2021
51Size and complexity: comparing cells and tissues
— Metazoan cells during development: simple shapes and small size
• Are cells simple building blocks with a limited diversity of shapes and size?
• In animals and plants, most cells exhibit simple morphology.
• Simple cell shapes underly complex tissue shapes: epithelial cells,
mesenchymal cells.
• Tissue multicellular complexity requires collective properties of large
number of simply shaped cells
• Single cell complexity emerges from self-organising properties of
cellular material
Elsev
Thomas LECUIT 2020-2021
52Summary
Complexity tends to increase with size
—Many small cells in large tissue
—Or single large cells
Stems from self-organising properties of living matter:
—Emergence of macroscopic order from homogenous
disordered/stochastic lower scale state
—Fluctuations amplified through feedbacks
Thomas LECUIT 2020-2021
53The cell as a complex organism
Thomas LECUIT 2020-2021
54The cell in 1665: simple and static
Robert Hooke
(1635-1703)
Micrographia (1665)
Thomas LECUIT 2020-2021
55The cell in 2020: complex and dynamic
T. Falk et al. Nature Methods volume 16, 67–70 (2019) Dong Li et al. and E. Betzig; Science 28 Aug 2015:
Vol. 349, Issue 6251, aab3500
DOI: 10.1126/science.aab3500
Thomas LECUIT 2020-2021
56The cell in 2020: numbers!
Model bacterium (E. coli) vs. Mammalian cell line (HeLa)
Diffusion limited
on-rate Clathrin-mediated
d
endocytosis
107-109 M–1 s-1 Passage across 1 min
membrane Diffusion over 10 μm
Ligand-induced 1-10 s
conformational change Channel Transporter
1 ms 0.1 μs 1-10 ms
Molecular motor
1 μm/s
DNA replication DNA replication
Diffusion over
ver 1 μm 103 nt/s 103 nt/min
10-100 ms
Cell movement - 10 μm/s Cell movement - 1 μm/min
Transcription
10-100 nt/s 10-100 nt/s
1 min/gene [1 kbp] 10 min/gene [10 kbp]
Cell cycle Cell cycle
1 hr 1 day
Translation
10 aa/s 10 aa/s
1 min/protein [300 aa] 1 min/protein [300 aa]
Flagellar rotation
100 Hz Protein folding
1 ms - 1 min
Cellular pool half-life (dominated by)
1s Metabolite (turnover) 1 min
10 min mRNA (degradation) 10 hr Sizes not to scale
1 hr Protein (dilution) 1 day Vbacteria : Vcell line
~1 : 1,000
Maya Shamir,1 Yinon Bar-On,1 Rob Phillips,2 and Ron Milo1
Cell 164, 2016 DOI http://dx.doi.org/10.1016/j.cell.2016.02.058
Thomas LECUIT 2020-2021
57The shape space of single cells
(A) (B) (C)
2 μm 10 μm 20 μm
(D) (E) (F)
• Extensive variety of shapes
• Extensive variety of size
20 μm 40 μm 50 μm
(G) (H) (I) (J)
80 μm 100 μm 200 μm
Thomas LECUIT 2020-2021
5 mm
58Equilibrium cell shapes
• surface tension: minimal surfaces
Gtot = γ •A γ = ƒ(cortical tension, adhesion)
(A) (B)
(C) (D)
Thomas LECUIT 2020-2021
59Cell shape as a dynamical steady-state
• Cell shape is dynamically but not genetically encoded. It is self-organised
(A)
(A)
area aspect y
ratio
n = 695 cells m2 x x/y
1,000
800
3
population 600
mean±s.d. 400 2
individual 200
1
100 75 50 25 100 300 500 700 100 75 50 25 100 300 500 700
cell count time (s) cell count cell count
10 m front
(B) radius speed
m m s–1
shape mode 1 area 90
0.3
70
mean
–2ı –1ı n = 710 +1ı +2ı 50 0.2
30
0.1
81.8% of
10
total variance
shape mode 2 aspect ratio 120 80 40 60 40 20
(B)
20 s 610 s 830 s 1,230 s
11.7% of
total variance
shape mode 3 angle
10 m
(C)
m 2 area aspect ratio µm s–1 speed
600 610s 830s 1,230s 4 0.4
2.5% of 3 0.3
400
total variance 0.2
2
shape mode 4 L/R asymmetry 200 0.1
1
400 800 1,200 1,600
time (s)
0.9% of
total variance
K. Keren et al and J. Thériot. Nature, Vol 453|475 2008|doi:10.1038/nature06952
Thomas LECUIT 2020-2021
60The cell as a complex organism
4 big problems
• Cell internal heterogeneity: compartmentation of activities
• Cell polarity: vectorial organisation
• Cell motility
• Cell size: 2020
Thomas LECUIT 2020-2021
61Cell size — volume
Statement of the problem:
• Cell size varies between cell types in Animals but within a given cell
type there is very little size variation (ex. epithelial cell). So cells control
their volume tightly.
—Why is cell size regulated?
• Cell size is tightly coupled to cell function, for example, neuron, oocyte,
red blood cells, Ciliates etc.
• Cell size is physically constrained, e.g.:
—diffusion of metabolites limits cell size.
—surface to volume ratio for exchange with environment
—diffusion of signalling molecules limits communication within cells
(unless other transport mechanisms operate such as motor driven
or by trigger waves)
—energetically: synthesis of ribosomes and translational capacity
limits cell growth. Given maximal rate of rRNA transcription, there
is a limit to cell growth, unless polyploidy or multinucleation (ex.
muscle cells, ciliates etc).
• Cell size is governed by protein synthesis, osmotic flow and cell cycle
which operate at different time scales: how is this integrated?
Thomas LECUIT 2020-2021
62Cell size — scaling
Statement of the problem:
• Cell size is tightly regulated
N
but varies strongly during embryonic
cleavage (by a factor of 2 for N divisions)
• Cells grow 2-fold before they divide or may grow while they increase
their ploidy
• As cells change their volume do internal organelles scale? What are the
mechanisms of scaling?
• When cells display symmetric structures (eg. flagella or cilia) how is the
size of these structures controled
Thomas LECUIT 2020-2021
63• Lectures
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