Download Lecture 12 BSE 652 21-2-2017 Maintenance of differentiated state

Lecture 12
Morphogenesis
Differentiation – 4
Cell-cell communication
BSE 652
21-2-2017
Maintenance of differentiated state
Extracellular matrices in the developing embryos
Fibronectin in the
developing frog
embryo. (A)
Fluorescent
antibodies to
fibronectin show
fibronectin
deposition as a
green band in the
Xenopus embryo
during gastrulation.
The fibronectin will
orient the
mesoderm
movements of the
cells.
Laminin
synthesizing
Collagen
synthesizing
mesenchyme
 Collagens are the most abundant ECM molecules, in fact they
constitute 25% of ALL proteins made in our body!
 Proteoglycans play major role in delivery of paracrine factors
 Fibronectin acts as a general adhesive molecule
 Fibronectin interacts with migrating cells through specific
molecules which aides in alignment of migrating cells to the ECM
 Laminins are major components basal lamina, secreted by
epithelial cells. The laminin-epithelial cell interaction is much
stronger than fibronectin-mesenchyme interaction
Location and formation of extracellular matrices
in the chick embryo. The scanning electron
micrograph shows the extracellular matrix at
the junction of the epithelial cells (above) and
mesenchymal cells (below). The epithelial cells
synthesize a tight, glycoprotein-based basal
lamina, while the mesenchymal cells secrete a
loose reticular lamina made primarily of
collagen.
Integrins
 Integrates ECM and
cellular cytoskeleton.
 ECM attachment
seems to be a major
survival signal
Speculative diagram
relating the binding of
cytoskeleton to the
extracellular matrix
through the integrin
molecule
ECM directed gene expression
ECM directed gene expression
Basement membrane-directed gene
expression in mammary gland tissue.
(A) Mouse mammary gland tissue
divides when placed on tissue culture
plastic. Cell division genes are on, and
the genes capable of synthesizing the
differentiated products of the
mammary gland (lactoferrin, casein,
whey acidic protein) are off. (B) When
presented with basement membrane
that contains laminin, the genes for
cell division proteins are turned off,
while the gene inhibiting cell division
(p21) and the gene for lactoferrin are
turned on. (C, D) Mammary gland
cells wrap the basement membrane
about them, forming a secretory
epithelium. The genes for casein and
whey protein are sequentially
activated.
Epithelial mesenchymal transition
Outline of EMT
Formation of mesoderm –
Mesenchymal cells delaminate
from the epiblast