module 4ab

Question 1

Cell-Cell adhesions

Answer 1

-seen in mature epithelia where strong anchorage of cell to cell exists
-transmembrane adhesion proteins span the plasma membrane, intracellular region is indirectly linked to cytoskeleton

Question 2

What are the two types of transmembrane adhesion proteins

Answer 2

1) cadherins (cell to cell attachment)
-found in cell-cell junctions
-anchored by catenins
-not found in fungi/plants
-stands for calcium dependent adhesion
-main component of adhesion in embryonic tissue
-3 types of classic cadherins:
a) E cadherin (epithelial cells)
b) N-Cadherin (nerve cells)
c) P-cadherin (placenta cells)
-invovled in homophillic interaction: each one has a knob and complementary pocket, knob of one cadherin binds to the pocket of the other
-have a domain: classical have 5 (rigid unit and each domain is are seperated by hinge region that is stabilizd by ca ions, if removed it becomes unrigid and floppy)
-interactions are selective (only form associations withsame type)
-twist gene
-intrcellular domain needed to link cadherin to actin cytoskeleton, need accessory proteins to do this since its indirect (the attachment of cadherin and actin is indirect so there are proteins called CATENINS between here)
2) Integrins (cell to ecm attachment)
-found in cell-matrix junctions
-achnored by diverse proteins
-named bc they integrate the extracellular and intracellular scaffolds
-on extracellular side: bind, found in adhesive proteins like fibronectin and laminin
-on icytoplasm side: bind to proteins that connect to actin filaments; dual binding allows cell to move by contracting actin filaments against fixed ecm

Question 3

What is shotgun

Answer 3

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.

Question 4

Cadherin homophillic

Answer 4

-form homodimers
-cadherins from one cell can bind to cadherins in neighbouring cell through HOMOPHILLIC INTETACTION; adjacent anchoring junction is symmetrical

Question 5

What happens if the ca ions of domain are removed

Answer 5

the ca ions are what seperate each domain from eachothe on a single cadherin
-if removed the hinges can flex and become floppy since ca gives it structure

Question 6

What is cadherin sorting out

Answer 6

refrs to association of similar cell types with eachother as long as hey are expressing same cadherin molecule (doesnt have to be same level of it) they can still be attached together

-this sorting out is also thought to occur during animal embryogensis 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 7

cadherins and tissue differntiation

Answer 7

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).

Some genes found to regulate mesenchymal differentiation
:twist gene negatively regulated E-Cadherin so this turned on turns epithelial cells into mesenchymal

Question 8

Cancer and twist gene

Answer 8

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

since turnign twist on changes epithelial cells to mesenchymal
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 9

What does turning on twist gene do

Answer 9

turn epi into mesenchymal so decreases epi

Question 10

what are catenins

Answer 10

-accessory proteins needed to attach cadherin to actin filament
increase in p120-catenin leads to increased cell-cell adhesion
p-catenin and beta-catenin link cadherins to actin cytoskeleton

Question 11

is beta catenin a transcription factor

Answer 11

yes

Question 12

Adherins junction

Answer 12

-organized cadherin-actin interactions are called this

in epi cells:
organized as continous adhesion belt (aka zonula adherens) beneath apical surface of cells
-tethered to bundles of contractile actin, forms a transcellular network so that an entire sheet of epidermal cells can act as a coodinated unit
-important during morphogensis
“epithelial sheet morphofgenisis”
-transcelluar adhesion allows: coordinated movement pf epidermal sheets
-allows for tightening or loosening of sections to result in different formation (look at slide 19)

Question 13

What is zonula adherns

Answer 13

anither name for continous adhesion belt of epithelial cell cadherin-actin interactions

Question 14

Occuluding junctions

Answer 14

AKA tight junctions or septate junction (invertebrates)
-sealing together of epdiermal cells to create barrier
-proteins for tight: claudulins and occludins and tricellulin
all needed to prevent leakage
different ones are associated with different degrees of permeability
-proetins for septate: claudulin

Question 15

Laminin

Answer 15

large glycoprotein and major component of basal lamina
-integrins are found within this

Question 16

4b sea urchin

Answer 16

just a card to sepearte the sections

Question 17

early development and gastrulation in sea urchins

Answer 17

-rapid specificity in blastomeres by products of zygotic genes
-small number of cells at start of gastrulation

1st and second cleavage is meridonial (top to bottom but they are right angles to eachother (making a cross if looking from above)
-produce equal sized blastomere
3rd: equitorial: produces two size classes of cells bc it is slightly unequal
4th cleavbage: results in three size classse since it makes an equal meridonial cut on top and uneual equitoral cut on bottom
;mesomeres (from meridonial division)
;macromeres: large
;micromeres: small (from unequal equitoral division)
5th division: 16-32 cells
meso divides equitorially (makes an1 and an2)
macro: divides meridonally to just double the number in that layer
micro: divides equitorally (makes small micromers and large micromeres)
6th: 32->60 an divide meridonally vegetal cells (macro and large micro) divide equitorally (small micro doesnt devide)
7th: 60-> 116
-blastocoel forms
9 and 10 occurs

at blastula all are same size and contact blastocoel fluid on inside
-blastomeres are now an epithelim connected by tight junctions

Question 18

meridonial cleavage vs equatorial

Answer 18

meridonial: splits it following north south line

equatorial: splits it following equatorial line from left to right

Question 19

why doesnt the small microneres divide at stage 6 and beyond

Answer 19

they express germline determinant VASA and some give rise to germ cells, retained in left coelomic pouch

Question 20

at the blastomere stage what do each type of cell do

Answer 20

after 9 and 10 divisions

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 21

Gastrulation overview; epithelial to mesenchym transition

Answer 21

endoderm invaginates, starts where micromeres are
-invaginations goes across blastocoel
-endoderm fuses with oral ectoderm mouth forms

1. vegetal pole flat
2. cells move inward forming archantron (due to actin contraction)
3. cells break free becoming primary mesenchym (convergent extension, cells polarize becomes narrower tissue and moves it forward)
4. keeps moving up, extension of cells form filopodia attach to ectoderm, secondary mesechyme now
5. archantron elongated by contraction of filopodia
6. mouth forms where archantron and ectroderm meet, now a continous digestive tract is made

epithelial cels alter junctions in order to do this so that they can move individually

Question 22

what is the archentron vs blastopore vs vegetal plate

Answer 22

Vegetal plate: vegetal pole region cells that flatten into this

archentron: vegetal plate invaginated 1/4 to 1/2 the way (invaginated region is archendtro)

blastopore: opening at vegetal pole

invagination occurs due to cell change shape (actin contraction causes it to invaginate, controlled by shroom gene) , changes in ecm

Question 23

what do non skeletogenicmesenchym cells for m

Answer 23

disperse when archaentoron meets blastocoel wall and form mesodermal organs,

Question 24

what do the large micromeres do

Answer 24

-become skeletal mesenchym (non skeletal mesenchym go on top of archentron and are where filopidia emanate from)
-extend filopidia
-settle in ventrolateral region (inside wall of blastocoel)
-fuse to form SYNCTICIAL CABLE (form axis of calcium carbonate spicules of larvalsksletal rods)

Question 25

are large micromeres following autonomous specification

Answer 25

yes
-they have the maternal determinant swhich determine what they are, they dont need other signalsto beome what the will (which is skeletal spicules)

small microperes do: the large micromeres produce paracrine and juxtacrine factors which specify their fate as non-skeletogenic mesechyme and endoderm), this is conditional specification

Question 26

if u isolate animal hemisphere alone what will happen

Answer 26

will not gastrulate, will all be ectoderm, u need the micromeres to be able to do this since micromeres are autonomous specification so they dont need other cells to tell them what to do they know that they are just skeletal spinucules and these cells will influence / induce ectoderm (so all tissue and nervous system) to become endoderm (inner gut and internal organs)

Question 27

What is the determinant specifies micromeres

Answer 27

transcriptional regulators: Disheveled protein and B catenin (wnt pathway: wingless signalling pathway, integrated idk read slide)

Dishevled protein : found local to vegetal pole and inherited by micromeres in 4th division, prevents degredation of Beta-catenin which enters nucleus to activate gene expression w Trancscriptoon factor

Question 28

What is WNT pathway

Answer 28

1. wnt binds to frizzled receptor
2. frizzled activated disheveled
3. activated disheveled inactivates glycogen synthase kinase 3 (this usualy prevent beta catenin from dissociating and targets it for degredation )
4. so now B catenin is free to associate with transcription factors and become actine in nucleus

so allows target genes to be activated (slide 63)

Question 29

How does beta catenin involved in micromere specification

Answer 29

increased Beta catenin (litium chloride inhibits B catenin degredation) means that all cells that have it will be transformed into endoderm and mesoderm since it accumulates in cells that will becomethis
overall, β-catenin induces fate of vegetal cells – and these, for the most part, become mesoderm and endoderm

inhibition of beta catenin causes all embryo to be ectoderm

Question 30

What is the determinant that autonomously specifies large micromere fate

Answer 30

This fate depends on activation of the wnt pathway, leading to increased activity of nuclear β-catenin as a transcription factor.

This increased activity is due to the maternally loaded protein Disheveled (Dsh) which was localized to the vegetal cortex prior to fertilization. Cells which acquired Dsh will become the progenitors of the skeletogenic mesenchyme.
So…ultimately – I would say the maternal determinant here is Disheveled.

Question 31

once oral ectoderm specified, what type of symmetry do we have

Answer 31

before radial now bilateral symmetry

Question 32

Nodal gene

Answer 32

the specification of the oral ectoderm breaks the pattern of radial symmetry during gastrulation – producing bilateral symmetry

after gastrulation the coelomic pouch of the left side develops into the imaginal rudiment, which will eventually emerge from the larval body as an animal that has radial symmetry.

BOTH processes involve expression of a gene called Nodal