Biol 303- Mod 4

Question 1

Cell-cell adhesions
Cell to cell adhesions are most clearly seen in?

Answer 1

Cell to cell adhesions are most clearly seen in mature epithelia - where there is strong direct anchorage of cell to cell.

Question 2

Transmembrane adhesion proteins span the plasma membrane - their intracellular region is usually indirectly linked to ?

Two fundamental types of transmembrane adhesion proteins?

Answer 2

Transmembrane adhesion proteins span the plasma membrane - their intracellular region is usually indirectly linked to the cytoskeleton.

Two fundamental types of transmembrane adhesion proteins:

the cadherins (generally cell to cell attachment)

the integrins (generally cell to ECM attachment)

Question 3

cadherins - are found in?

integrins - are found in?

read table 19-2

Answer 3

cadherins - are found in cell-cell
junctions of epithelial cells and are frequently anchored by catenins

integrins - are found in cell-matrix junctions and are anchored by diverse collection of proteins

these molecules bridge transmembrane adhesion molecules to a cytoskeletal filament

Question 4

Cadherins

Cadherins - present in all? )

The name cadherins derives from?

How were cadherins discovered?

Some types of cells (especially embryonic cells) can be readily dissociated by ?

It was found that reassociation could be prevented by ?

Answer 4

Cadherins - present in all multicellular animals, but absent from fungi and plants (not found in prokaryotes)

The name cadherins derives from calcium dependent adhesion.

How were cadherins discovered?

Some types of cells (especially embryonic cells) can be readily dissociated by stripping calcium out of the extracellular medium using a chelating agent such as EDTA. (sometimes you also need a protease such as trypsin).

If dissociated cells are placed back into normal tissue culture medium, they can reassociate.

It was found that reassociation could be prevented by addition of certain monoclonal antibodies - which, as it turned out, were specific for cell adhesion molecules. When bound to their targets, the antibodies blocked the ability of dissociated cells to reassociate.

Question 5

There are many types of cadherins - they are the main component of adhesion in embryonic tissues.

What happens in drosophila embryo for mutation in gene ?

Answer 5

There are many types of cadherins - they are the main component of adhesion in embryonic tissues.

Interestingly, in Drosophila embryos homozygous for a mutation in the gene encoding E-cadherin literally fall apart. The gene, named after the embryonic lethal mutant phenotype, is called shotgun.

In early mouse embryo development the blastula undergoes compaction at the 16-32 cell stage. Compaction is an E-cadherin dependent event. Mouse embryos lacking E-cadherin also fall to pieces.

Question 6

First found in epithelial cells?-

First found in nerve (also muscle)?-

First found in placenta (and epidermis) ?

These are the so-called ?

Cadherins, like many junctional proteins, are also important in?

Answer 6

First found in epithelial cells - so named E-cadherin

First found in nerve (also muscle) - named N-cadherin

First found in placenta (and epidermis) - named P-cadherin

These are the so-called “classical cadherins” - they are closely related throughout their sequence and perform well defined adhesive functions

Cadherins, like many junctional proteins, are also important in cell-signalling.

There are lots of non-classical cadherins - not so related in sequence and having a variety of functions - the cadherin superfamily in humans has about 180 members.

Question 7

The Cadherin - homophilic interaction

Cadherins form?

Dimeric cadherins from one cell can bind to cadherins in?
What happens in process?

Answer 7

Cadherins form homodimers. Dimeric cadherins from one cell can bind to cadherins in neighbouring cells through a homophilic interaction; the anchoring junction is symmetrical.
Binding occurs at the N-terminal tips of the cadherin molecules (furthest away from the plasma membrane) - each cadherin has a knob and complementary pocket. The knob of one cadherin binds in the pocket of an opposing cadherin molecule.

Question 8

The Cadherin domain
How many domains classical and non classical cadherines have?
Their characteristics?

Answer 8

Cadherin molecules also have a characteristic motif - the cadherin domain. Classical cadherins have 5 such domains, the non-classical cadherins may have as many as 30 domains.

Question 9

Cadherin domains form a rigid unit and adjacent cadherin domains are separated by a?

Answer 9

Cadherin domains form a rigid unit and adjacent cadherin domains are separated by a hinge region that is stabilized and made rigid by Ca+2 ions.

Removal of Ca+2
- hinges can flex and the structure becomes floppy.

Question 10

Cadherin-cadherin interactions are selective

There are many different cadherin molecules - and they tend to form associations with?

Disaggregated embryonic cells can be randomly?

Answer 10

There are many different cadherin molecules - and they tend to form associations with only the same type.

Disaggregated embryonic cells can be randomly reaggregated - remarkably, they tend to sort themselves out according to cell type, which relates to which cadherins are expressed.

Question 11

Cadherin-cadherin interaction promotes association of similar cell types

Sorting-out can also occur among cells that are?

Answer 11

Sorting-out can also occur among cells that are expressing different levels of the same cadherin molecule.

Question 12

Cadherin expression and tissue differentiation

The same sorting interaction is thought is also occur during?

The separation of the neural tube from the ectoderm, for example, is associated with?

Answer 12

The same sorting interaction is thought is also occur during normal animal embryogenesis and may drive tissue differentiation.

The separation of the neural tube from the ectoderm, for example, is associated with changing patterns of E-cadherin and N-cadherin expression.

Question 13

The expression of cadherin in dispersed?

During development the opposite process is also seen - where cells leave?

Answer 13

The expression of cadherin in dispersed unattached cells (mesenchymal cells) can cause them to come together and form an epithelium.

During development the opposite process is also seen - where cells leave an epithelium - this is called an epithelial to mesenchymal transition (EMT).

When epithelial cells undergo EMT, genes encoding proteins that are components of junctional complexes (adherens junction, tight junction, gap junction) are often down-regulated.

Question 14

Cadherin expression and tissue differentiation

A set of regulatory genes have been identified that regulate?

The product of the highly conserved gene twist (a transcription factor) has been found?

Turning on twist turns epithelial cells into?

Most cancers originate in ?

. Some types of cancer are associated with mutations in the?

Answer 14

A set of regulatory genes have been identified that regulate mesenchyme differentiation - (slug, snail, twist)

The product of the highly conserved gene twist (a transcription factor) has been found to negatively regulate E-cadherin gene expression.

Turning on twist turns epithelial cells into mesenchymal cells.

Most cancers originate in epithelia and the E-M transition is one aspect of spreading in malignant or metastatic tumours.

Blocking twist expression can stop cancer cells from spreading by forcing them back to their epidermal character. Some types of cancer are associated with mutations in the E-cadherin gene.

Question 15

Catenins link cadherins to cytoskeleton

Cadherins also have an intracellular domain which is necessary for?

Catenins are key accessory proteins in cadherin - filament interactions. Loss of p120-catenin leads to ?

p120 catenin and-catenin link cadherins to?

Answer 15

Cadherins also have an intracellular domain which is necessary for the linkage of cadherin to the actin cytoskeleton (in the case of adherens junctions)

This linkage, however, is indirect and requires accessory intracellular anchor proteins.

Catenins are key accessory proteins in cadherin - filament interactions. Loss of p120-catenin leads to loss of cell-cell adhesion. (Increases of p120-catenin lead to increased adhesion).

p120 catenin and-catenin link cadherins to the actin cytoskeleton.

-catenin is also a transcription factor!

Question 16

The Adherens Junction

Organized cadherin-actin assemblies are called?.

In epithelial cells these junctions are organized as a?

The adherens junction as a continuous belt is also known as the?

The adherens junctions of epithelia are tethered to bundles of?

Answer 16

Organized cadherin-actin assemblies are called adherens junctions.

In epithelial cells these junctions are organized as a continuous adhesion belt beneath the apical surface of cells.

The adherens junction as a continuous belt is also known as the zonula adherens.

The adherens junctions of epithelia are tethered to bundles of contractile actin - this form a transcellular network such that an entire sheet of epidermal cells can act as a co-ordinated unit. (important during embryogenesis - morphogenesis.)

Question 17

See slide 19

Question 18

The Occluding Junction (Tight or Septate)

60% of all tissues in a typical vertebrate body are?.

Epithelia are generally polarized and are anchored on the?

The environment (space and fluid) on the apical side of an epithelium is separate from?

The sealing together of epidermal cells to create this barrier (often a selectively permeable barrier) is achieved by?

Answer 18

60% of all tissues in a typical vertebrate body are epithelial.

Epithelia are generally polarized and are anchored on the basal side to the basal lamina but are free on the apical side.

The environment (space and fluid) on the apical side of an epithelium is separate from the space and fluid on the basal side (demonstrated by tracer labelling experiments as above).

The sealing together of epidermal cells to create this barrier (often a selectively permeable barrier) is achieved by occluding junctions - which in vertebrates are called tight junctions (in invertebrates they are different and are called septate junctions).

Question 19

The proteins that form the sealing strands are knowns as?

Different claudins members are found in different cell types - associated with different degrees of?

Answer 19

The proteins that form the sealing strands are knowns as claudins and occludins. A third protein known as tricellulin is also required to prevent leakage at the tight junction.

Different claudins members are found in different cell types - associated with different degrees of permeability and selectivity of permeability (eg. selective retention of Mg+2 ions in kidney).

Question 20

Invertebrates have a different type of occluding junction called?

Septate junctions also use?

Answer 20

Invertebrates have a different type of occluding junction called the septate junction (much nicer to look at by EM).

Septate junctions also use claudin-related proteins.

Question 21

Fibronectin: A very large (460 kDa) glycoprotein dimer synthesized by numerous cell types and secreted into the ?
Functions as a?

Integrins: A family of receptor proteins so named because they integrate ?
On the extracellular side, integrins bind to the ?
, found in ?
On the cytoplasmic side, integrins bind to ?

This dual binding enables the cell to move by ?

Answer 21

Fibronectin: A very large (460 kDa) glycoprotein dimer synthesized by numerous cell types and secreted into the extracellular matrix. Functions as a general adhesive molecule, linking cells to one another and to other substrates such as collagen and proteoglycans, and provides a substrate for cell migration.

Integrins: A family of receptor proteins so named because they integrate the extracellular and intracellular scaffolds, allowing them to work together. On the extracellular side, integrins bind to the sequence arginine-glycine-aspartate (RGD), found in several adhesive proteins in extracellular matrices, including fibronectin, vitronectin (found in the basal lamina of the eye), and laminin. On the cytoplasmic side, integrins bind to talin and α-actinin, two proteins that connect to actin microfilaments. This dual binding enables the cell to move by contracting the actin microfilaments against the fixed extracellular matrix.

Question 22

Laminin: A large glycoprotein and major component of the basal lamina, plays a role in ?

Cadherins: Calcium-dependent adhesion molecules. Transmembrane proteins that interact with other cadherins on adjacent cells (homotypic interaction) and are critical for ?

a mixture of cells expressing different cadherins (there are several different cadherins) cells tend to sort-out according to ?

Answer 22

Laminin: A large glycoprotein and major component of the basal lamina, plays a role in assembling the extracellular matrix, promoting cell adhesion and growth, changing cell shape, and permitting cell migration.

Cadherins: Calcium-dependent adhesion molecules. Transmembrane proteins that interact with other cadherins on adjacent cells (homotypic interaction) and are critical for establishing and maintaining intercellular connections, spatial segregation of cell types, and the organization of animal form.

a mixture of cells expressing different cadherins (there are several different cadherins) cells tend to sort-out according to which cadherin they express as well as the amount of that cadherin expressed

Question 23

4B

See answer slide for intro

Answer 23

Early development and gastrulation in sea urchins (echinoderms), snails (gastropods molluscs), ascidians (tunicates =sea squits), and C. elegans (nematode worm)

immediate activation of zygotic genes

rapid specification of blastomeres by products of zygotic genes and by maternally provided transcripts and proteins

relatively small number of cells at start of gastrulation

Question 24

Echinoderms

model system
Characteristics of echinoderms?

Answer 24

model system
-Cheap, free actually you go get them.
-Initially a model for cleavage and cell fate mapping. Came back as genomic model
-Large number of progeny. 200,000 to 1 million eggs.
-Short life cycle (4 days to pluteus larva).
-Really no genetic tools
-No stocks
-Disadvantage is body plan

Question 25

See slide 30 for sea urchin life cycle

Question 26

Early development and gastrulation in sea urchin

1st cleavage is ?

2nd cleavage is also?

3rd cleavage is?.

1st and 2nd cleavages produce?
, but the 3rd cleavage produces?

The 4th cleavage results in three cell size classes?

Answer 26

1st cleavage is meridional (N-S)

2nd cleavage is also meridional, but at right angles to the first cleavage plane.

3rd cleavage is equatorial.

1st and 2nd cleavages produce equal sized blastomeres, but the 3rd cleavage produces two size classes of cells.

The 4th cleavage results in three cell size classes, the mesomeres (from equivalent meridonial division), and the large macromeres and the tiny micromeres (from unequal equatorial divisions) .

Question 27

Early development and gastrulation in sea urchin

5th division
the 8 animal mesomeres divide?
4 macromeres divide?
later, micromeres divide?

6th division
small micromeres cease dividing until?
animal hemisphere cell divide?
whereas vegetal divide?

7th division
animal hemisphere cell divide ?
whereas vegetal divide?
now a blastula as blastocoel forms ?

Answer 27

5th division (16 cells  32 cells)
the 8 animal mesomeres divide equatorially to produce two tiers (an1 & an2)
4 macromeres divide meridionally to give 8 cells below an2 tier
later, micromeres divide unequally – 4 small micromeres & 4 large micromeres

6th division (32 cells  60 cells) ( = 4 + 2(28))
small micromeres cease dividing until larval stage
animal hemisphere cell divide meridionally whereas vegetal divide equatorially

7th division (60 cells  116 cells) ( = 4 + 2(56))
animal hemisphere cell divide equatorially whereas vegetal divide meridionally
now a blastula as blastocoel forms > further divisions are less regular

Question 28

rapid cell cleavage divisions – invariant – continue through ?

at blastula all cells are ?

blastomeres are now an?

outer cell surface (apical) becomes?

cells at animal pole produce and secrete an enzyme that breaks down?

Answer 28

rapid cell cleavage divisions – invariant – continue through 9th or 10th divisions

at blastula all cells are same size & contact blastocoel fluid on inside (Basal) and hyaline layer on outside (apical)

blastomeres are now an epithelium connected by tight junctions

outer cell surface (apical) becomes ciliated

cells at vegetal pole thicken – forming the vegetal plate

cells at animal pole produce and secrete an enzyme that breaks down the fertilization envelope – embryo becomes a free-swimming hatched blastula

Question 29

Sea Urchin Embryogenesis
Gastrulation

Gastrulation

Gastrulation initiated when?
Vegetal endoderm buckles (invagination) and extends across?
Endoderm fuses with?

Answer 29

Gastrulation

Gastrulation

Gastrulation initiated when micromeres ingress (EMT)
Vegetal endoderm buckles (invagination) and extends across blastocoel
Endoderm fuses with oral ectoderm mouth forms

Question 30

EMT

Epithelial to mesenchymal transition

Blastula cells are an epithelium?
Blastocoel lined with?
Mesenchyme cells detach ?

Answer 30

Epithelial to mesenchymal transition

Blastula cells are an epithelium with tight junctions, adherens junctions
Blastocoel lined with ECM (in sea urchins this turns over very quickly)
Mesenchyme cells detach (degrade basal lamina) and move into blastocoel and migrate on ECM

Question 31

Epithelial to mesenchymal transition

Epithelial cells held together with?
Cells eventually detach and?
EMT conserved and regulated by?

Answer 31

Epithelial to mesenchymal transition

Epithelial cells held together with cell junctions. These are altered (tight junctions dissolved), adherens junctions lighten up and cells can change shape.
Cells eventually detach and migrate as individuals
EMT conserved and regulated by snail and twist genes in all organisms

Question 32

Ingression of skeletogenic mesenchyme – an epithelial to mesenchyme transition

large micromere descendants lose their affinity for?
and develop a strong affinity for ?

Answer 32

large micromere descendants lose their affinity for neighbouring cells and for the hyaline layer and develop a strong affinity for proteins that line the blastocoel (process involves changes in proteins such as fibronectin, integrin, laminin, cadherin)

Question 33

Sea Urchin Embryogenesis

Gastrulation

Vegetal plate thickens and?
Invagination is the?
Vegetal plate buckling due to?
Vegetal opening of archenteron is the?

Answer 33

Gastrulation

Vegetal plate thickens and buckles (invagination)
Invagination is the archenteron lined with endoderm
Vegetal plate buckling due to apical contraction
Vegetal opening of archenteron is the blastopore, will become the anus

Question 34

Apical constriction

Apical Constriction

Common mechanism in?
Cells in epithelium are?
Vegetal plate buckling due to?

Actin belts in apical surface contract and?
Controlled by a gene called?

Answer 34

Apical Constriction

Common mechanism in epithelial sheet folding
Cells in epithelium are polarized
Vegetal plate buckling due to apical contraction
Basal surface on basal lamina (most cells need to be attached to survive)

Actin belts in apical surface contract and reduce surface area of cells (actin+myosin IIb)
Controlled by a gene called shroom
Form wedge shape cells

Question 35

Archenteron extends further into?

Answer 35

Archenteron extends further into blastocoel via convergent extension

Question 36

Convergent Extension

Gastrulation

convergent extension active process?

Answer 36

Gastrulation

convergent extension active process
Cells polarize, intercalate past each other
Direction of intercalation drives direction of tissue extension