Alejo Rodriguez-Fraticelli, from Dr Fernando Martin-Belmonte’s laboratory in the CBMSO in Spain, has recently published with co-workers a paper in the Journal of Cell Biology in which they describe their approach to epithelial cells morphogenesis and uncover the role of cell confinement on epithelial polarity via peripheral actin contractility. The team sheds light on a phenomenon that is crucial to understand the physiology of the organs, but also the mechanisms underlying the development and progression of agressive epithelial cancers.

1. Epithelial morphogenesis:
Let there be a lumen
Figure 1: Caco-2 cells at 5 days post
seeding. Scale bar: 10 µm. Red:
F-actin, green: α-catenin, blue: nuclei.
Courtesy of Alejo Rodriguez-Fraticelli
and Minerva Bosch.
“We conclude that cell confinement controls
nuclear-centrosomal orientation and lumen
initiation during 3D epithelial morphogenesis”
Alejo Rodriguez-Fraticelli, Centro de Biologia
Molecular Severo Ochoa (CBMSO), CSIC-UAM,
Madrid, Spain
Alejo Rodriguez-Fraticelli, from Dr Fernando Martin-Belmonte’s
laboratory in the CBMSO in Spain, has recently published with co-
workers a paper in the Journal of Cell Biology in which they describe
their approach to epithelial cells morphogenesis and uncover the role of cell
confinement on epithelial polarity via peripheral actin contractility. The team sheds
light on a phenomenon that is crucial to understand the physiology of the organs, but
also the mechanisms underlying the development and progression of agressive epithelial
cancers.
Epithelial organs, such as lungs, intestines or kidneys, are involved in the majority of vital functions
in life. They are essentially formed by a monolayer of epithelial cells surrounding a central lumen
(Figure 1). The formation of this space into a cellular structure results from the differentiation of
individually polarized cells, that acquire collective polarity. Alejo’s work was inspired by the effect of
cell confinement on ciliogenesis.In his ground breaking paper,Alejo used micropatterns to investigate
the role of cell confinement in the acquisition of 3D cell polarity and lumen formation.
Alejo used disc-shaped micropatterns coated with collagen or
laminin to study the role of cell confinement on cell spreading,
and to induce 3D lumen formation from single MDCK cells. His
observations led to the conclusion that physical cell confinement
was sufficient to promote lumen formation regardless of the
substrate to which the cells are attached. In conditions
promoting cell spreading, such as seen on large collagen
discs, lumen formation was impaired.

2. Further reading:
1. Rodríguez-Fraticelli AE, Martín-Belmonte F. Mechanical control of epithelial lumen formation. Small GTPases. 2013;4(2).
2. Rodríguez-Fraticelli AE,Auzan M,Alonso MA, Bornens M, Martín-Belmonte F. Cell confinement controls centrosome positioning and lumen
initiation during epithelial morphogenesis. J. Cell Biol. 2012;198(6):1011–1023.
3. Pitaval A,Tseng Q, Bornens M,Théry M. Cell shape and contractility regulate ciliogenesis in cell cycle-arrested cells. J Cell Biol.
2010;191(2):303–312.
The actin cytoskeleton is a
mechanical sensor that detects
modifications in the microenvironment and
modifies cell behavior and shape to control
cellular processes. Alejo finely analyzed the effect of
cell confinement on lumen formation and on the actin
cytoskeleton with different sizes of disc-micropatterns. In high
confinement conditions and after cell division, most centrosomes
were oriented toward the lumen initiation site at the center of the
micropattern,andtheGolgiapparatuswaspolarizedtowardsthejunctions.
In low confinement conditions, cell spreading impaired nuclear-centrosomal
positioning and lumen initiation.
Alejo also analyzed myosin II which regulates actin contractility, the main cellular
response to changes in cell confinement and consequent cell spreading. He observed that
in low confinement conditions, myosin II inhibition suppresses peripheral actin contractility and
rescues centrosomal reorientation and lumen morphogenesis.
His investigation of aPKC, which is required for lumen formation, led to
the conclusion that its activity is necessary to keep the centrosome in the
proper position for lumen initiation.
Dr Michel Bornens, CSO of CYTOO, commented this paper: «Alejo’s
work is remarkable, since he succeeded in addressing the role of
cell confinement in the acquisition of 3D epithelial cell polarity
and lumen formation. In this paper, he also shows that tumor
suppressor kinase LKB1 and the RhoA signaling pathways
regulate peripheral actomyosin II-mediated contractility and
lumen initiation. Further studies will be needed to clarify the
loss of polarity in the mechanism of cancer initiation and
spreading.»
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Investigating peripheral
actin contractility
Figure 2: MDCK cell division on a disc
micropattern. Green: F-actin, Red:
ß-catenin, Blue: nuclei.