week 2 - cell adhesion

many animal cells are either _________ or __________ tissue

connective or epithelial tissue

what is epithelial tissue

cells directly connected to each other with minimal extracellular matrix

what is connective tissue

cells dispersed through extracellular matrix

epithelial cells line what?

surfaces, cavities, organs

examples of epithelial cells

1. protective epithelial cell layers on the surface of organism (SKIN)

2. absorptive epithelial cells lining a cavity of the organism (digestive tract)

3. epiithelial cells surrounding and defining organs

epithelial cells are _________

POLARIZED. (they define inside vs outside of the organism or tissue)

epithelial structure and function requires

junctional complexes:

• tight junctions

• cell-cell anchoring junctions

  • adherens junction (actin)

  • desmosome (intermediate)

• chanel-forming junction

  • gap junction

• cell-matrix anchoring junctions

  • actin-linked cell-matrix junction

  • hemidesmosome (intermediate)

cell-cell junctions are usually mediated by

cadherins

cell-extracellular matrix junctions are usually mediated by

integrins

cadherins are what type of proteins?

TRANSMEMBRANE proteins expressed by both cells

cadherins interact in ___________ interactions of their ____________ domains

homophilic interactions

extracellular domain

what do cadherin interactions REQUIRE

Ca2+ (to make it rigid/stiff)

cells can sort into groups based on _______ cadherin interactions

homophilic

cadherins for homophilic interactions with thei extracellular domains to _______________ link adjacent cells and __________ interact with _______ filaments

directly

indirectly interact with actin filaments

cadherins interact in patches to form a strong

adhesion belt

adhesion belts can mediate _____

morphogenesis

role of cadherins in morphogenesis (ex: Drosophila)

cells express different cadherins to establish new interactions and ensure nueral tube closure (due to homophilic binding)

domains like basal domain, apical domain, basolateral domain are defined and maintained by

tight junctions

tight junctions are formed by

occludins and claudins

do occludins and claudins directly or indirectly link adjacent cells?

directly! (homophilic interactions)

tight junctions limit _______ of membrane proteins

diffusion

path that glucose takes to get into the blood

1. active transporters must move glucose into the epithelial cells on apical domain

2. passive carriers in the basolateral domain allow glucose to diffuse out of the epithelial cell into the connective tissue/blood

3. tight junctions keep the correct transporters in their correct domains

Integrin heterodimers mediate

cell-to-cell-matrix junctions

integrins anchor actin filaments to the

extracellular matrix

integrins ______ interact with actin filaments

INDIRECTLY

cell-matrix junctions play roles in both

epithelial and connective tissue

role of cell-matrix junctions in epithelial tissue

adhesion to the basal lamina and extracellular matrix

cell-matrix junctions role in connective tissue

cell interaction with the extracellular matrix and cell movement

what junction forms first and why?

• adherens junctions form first

• they provide polarity cues to define apical from basolateral domain

where do tight junctions form relative to the adherens junctions

APICAL to adherens junctions

cell polarity can be established by

extrernal or internal signals

1. sperm entry

2. chemoattractant by bacteria

an initial landmark can generate

subsequent elaboration

3 key components of cell polarity define a functional eputhelium

1. intracellular trafficking

2. cytoskeletal organization

3. cell cohesion

multicellular development; does it occur in adults?

yes (eg- skin flaking off)

when does embrogenesis start and end

starts after fertilization, ends just before birth

what does morphogenesis mean? what are the three processes involved

generation of shape

1. cell internalization

2. elongation

3. fine repositioning of cells

what is gastrulation?

change from ball of cells to embryo with a gut and 3 germ layers

morphogenesis during gastrulation forms 3 key tissue layers

ectoderm, mesoderm and endoderm

ectoderm forms the

epidermis and nervous system

mesoderm forms the

muscles, connective tissue, bones, blood, kindeys, etc

endoderm forms the

gut, lungs, pancreas, liver etc.

what is ingression

when individual cells detach from the outer cell layer and migrate (this is an epithelial-to-mesenchymal transition that forms loose, undifferentiated connective tissue)

what is delamination

these cells form a new cell layer, the mesoderm

cell internalization by ingression/delamination forms the

mesoderm

why must epithelial to mesenchymal transitions be carefully controlled

uncontrolled can cause cancer

what is invagination?

attached cells in an epithelial cell sheet are pulled into the middle of the embryo while remaining attached

what is involution

cells curl in and grow to form the endoderm

cell internalization by invagination/involution forms the

endoderm

___________ is essential for invagination/involution

cell adhesion

cells from what part of the 3 key tissue layers form nueral plate cells? and by what process?

ectoderm

invagination/involution

so formation of what two things uses invagination/involution?

1. gut tube (endoderm formed)

2. nueral tube

what is convergent extension

cells can move as individuals or as a group to form different shapes, called

collective cell migration

2 types of cell migration

chain-type migration involves less adherent cells

sheet-type migration involves more adherent cells

elongation can occur via

1. convergent extension

2. mass cell migration

3. cell growth (only if asymmetric)

4. cell division (only if asymmetric)

5. matrix desposition (only if asymmetric)

plant cells often grow by

directional expansion

due to (asymmetrically distributed) cellulose constricting plant cell expansion, forcing expansion in one direction

plant cell wall deposition is guided by

microtubules

disorganised microtubules will disrupt

plant cell elongation

what types of cell are repositioned by whole-cell migrations

cerebral cortex cells

axons are positioned by

migration of cell extension (attractants direct the extensions of the growth cone in a particular direction)