Apical polarity in three-dimensional culture systems: where to now? Page: 5 of 10
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the cells behave (for a detailed discussion see ). S1 cells are grown in a defined media with
only a few essential additives  whereas MCF10A cells are grown in 5% horse serum plus
additional additives . Serum has been a boon for cell biologists as it can support the growth
of most cells, but the plethora of components in serum are still poorly defined and the product is
subject to considerable batch-to-batch variation. Therefore, experiments using serum cannot be
As a proof of the above principle, Plachot et al.  find that the standard medium used for
MCF10A cells nearly abolished apical polarity when used to grow S1 cells in lrECM.
Conversely, when MCF10A cells were cultured in S1 medium, some of the acini (about 5%)
organized apical polarity. There are clearly cell-intrinsic differences between the two cell lines
because under these conditions 65% of Si acini contained apical polarity. Nevertheless, it is
clear that MCF10A cells went from 0% to 5% and S1 from 5% to 65% apical polarity with the
change of medium .
The importance of the extracellular matrix
It took decades from the classical studies of Michalopoulos and Pitot  and Emerman and
Pitelka  on floating collagen gels before other laboratories started to pay serious attention to
the importance of ECM in tissue specific gene expression in cultured cells. The presence of
a basement membrane (BM) in floating collagen gels was shown initially by electron microscopy
. Studies from the Bissell laboratory established that cells on floating collagen gels 
produce an endogenous BM and that the BM molecules are crucial for formation of tissue
specific form and function [15-17]. The BM is a form of ECM rich in collagen IV and tissue-
specific laminins that underlies epithelia and is in direct contact with the epithelial cells as well
as with other cell types (for example, endothelial and fat cells). In vivo, epithelial polarity is
established along with the formation of a BM as organs are formed. Laminin-111 is an important
component of both the embryonic and mammary gland BM as well as a major component of
lrECM; it usually polymerizes into a multivalent signaling scaffold at the surface of cells and
tissues. Studies on embryonic development previously reported that type IV collagen likely
stabilizes BMs  and is necessary for embryonic development. The assembled BM serves
multiple functions as a scaffold, a barrier and a signaling entity necessary for organization of the
tissues and organs.
Petersen et al.  showed formation of a human derived BM when human breast cells were
grown in mouse-derived lrECM gels. Plachot et al.  also find a continuous BM in their 3D
cultures. What is important here is their finding - reminiscent of the embryonic BM - that type IV
collagen most likely stabilizes the laminin-111 polymer in 3D cultures of mammary cells,
and that this may be directly related to the capacity of S1 acini to establish apical polarity (Figure
Plachot et al.  selected the S1 cell line for further study because of its ability to form apical
polarity, and compared the behavior of cultured S1 cells on multiple substrata. A number of
biological matrices, such as those isolated from the EHS tumor  (MatrigelTM or Cultrex
BM) and synthetic substrata (for example, PuraMatrixTM), were tested. Th e only substrata that
allowed formation of acini with basal as well as apical polarity were those that gelled and
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Inman, J. L. & Bissell, Mina. Apical polarity in three-dimensional culture systems: where to now?, article, January 21, 2010; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc830118/m1/5/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.