Chapter 9 Morphogenesis

Question 1

Morphogenesis, three main ways through which it is achieved :

Answer 1

Cell migration: cell going epithelial to mesenchymal and heading out.
Changes in cell adhesion:
Coordinated changes in cell shape.

Question 2

cadherins are a :

Answer 2

Calcium dependent cell to cell cohesion molecule. A cadherin cannot adhere without the c, for calcium.

Question 3

Multiple receptor types use cadherins :

Answer 3

Adherins: which utilize actin attached to the cadherins through catenins in order to mediate attachment.
An adherin since it is attached to a dynamic molecule is dynamic… ok, that was likely garbage…

Question 4

The other cell to cell type utilizing cadherins was a desmosome. A desmosome :

Answer 4

Mediates cell to cell adhesion between molecules using cadherins (calcium dependent) but does desmosomes anchor on microtubules within the cell.

Question 5

Ig superfamily Ig CAM

Answer 5

An Ig cam is an immunoglobulin cell adhesion molecule. Each Ig CAM will use at least one ig-like domain, they will generally have multiple. This is a calcium independent system, igCAM is generally, but does not have to be a homophillic system.

Question 6

Integrins:

Answer 6

integrins interconnect to the the extracellular matrix, and to actin on the inside of the cell. Integrins complex and allow the to detect the ECM and ‘talk’ with it.

Question 7

actin = microfilaments

Answer 7

actin = microfilaments

Question 8

What is the predominant linkage molecule for cell to cell adhesion?

Answer 8

Cell to cell adhesion predominately regulated by cahderins.

Question 9

What mediates the majority of adhesion between cells?

Answer 9

Cadherins are the predominate mediator of adhesion between cells.

Question 10

What molecule interlinks cadherins to actin in adherens?

Answer 10

catenins, including our friend beta catenin.

So beta catenin is both a cadherin to actin mediator of binding, and a transcriptional regulator! o.O

Question 11

Integrins a heterodymeric, proteins responsible for mediating cell to cell interactions.

Answer 11

This means that the there will be two (di) different (hetero) protein subunits involved in actin. Of course, integrins complex with the ECM.

Question 12

Both cadherins and integrins are associated with the signalling pathways for cancer…

Answer 12

The fact the integrins and cadherins are also both involved in cancer signaling pathways are not surprising, as we know that these cells are associated with mediating cell to cell interactions including growth differentials between

Question 13

Cells have complex ECMs, which can very and intercommunicate with the cells within that matrix.

Answer 13

We see that many supportive and instructive roles are played by the ECM. Important signaling molecules can be housed in the intracellular matrix. These signals can become placed in the ECM by surface proteins or by diffusion then attachment.

Question 14

How does differential adhesion affect molecules.

Answer 14

Molecules which adhere more strongly will make a circle if clumped with cells with weaker adhesion. ( you can see with presumptive neural and presumptive epidermal cells (neural will go inwards), this makes sense, because neurons are indeed under the skin… but I do not believe this is how they place themselves under the skin.

Question 15

Like sticks to like…

Answer 15

This is the way of cells.

Question 16

So there is two ways to sort cells through differential adhesion. Name them.

Answer 16

Ok, watch me.
One way is that you could have cells with two different types of cadherin (or cell adhesion molecule), the one with the greater adhesion will go to the center (assuming they are producing roughly equal amounts of the molecule.
Another way is to have both cell types producing the same molecule, let us say E-cadherin, but they produce it in significantly different proportions, this would also cause the cells with the highest production of cadherins will become centralized.

Question 17

Nanog and gata6 in the early embryo (blastocyst) are an example of sorting via use of different cell adhesion molecules

Answer 17

Where nanog and gata6 is dictated by a stochastic arms race

Question 18

What causes compaction of the embryo at around the 16 cell level.

Answer 18

This causes compactions because a spike in E-cadherin will allow the cells to associate more strongly/tightly

Question 19

Apical constriction. Let’s talk about it.

Answer 19

Apical constriction is when cell constrict the size of on side of their cell (a portion of the cell facing the apical portion), apical constriction causes an invagination of the cell

Question 20

intercalation:

Answer 20

intercalation is the process of cells sliding between layers of other cells (or a between cells which where formally associated with each other), generally these cells stay there after intercalation but they do not have to.

Question 21

invagination:

Answer 21

Invagination is the most simple result which can come from apical constriction, in invagination we see apical constriction, and cells, either in a tube, or single point, are ‘pushed’ towards the center of the structure.

Question 22

Ingression:

Answer 22

Ingression involves a epithelial to mesenchymal (and often back to epithelial) shift, it is the migration of cells into a structure.

Question 23

Involution:

Answer 23

Involution starts in a similar manner to a invagination, where the cells begin to poke towards the center, then however they are sucked inside, and travel parallel to the walls of the sphere, it is as if we had a predominately deflated beach ball and began to try to stuff the beach ball inside itself so that it would end as a half circle, cells are more dynamic and do not have to end as a half circle, but this mechanism is used by xenopus

Question 24

Epiboly:

Answer 24

Epiboly is the spread of sheet of cells over a surface, we see this in mouse development when the hypoblast spreads over the trophoblast.

Question 25

Convergent extension:

Answer 25

This mechanism is fully based on intercalation. Cell layers slide together, this makes it so while they where previously fat and short, they are now tall and skinny, or visa versa.

Question 26

Sea urchin begins with what from its blastula state?

Answer 26

It will start with apical constriction, leading to the formation of the an invagination.

Question 27

The mesoderm which was the most apical at the point of apical constriction, and has now been greatly internalized undergoes an epithelial to mesenchymal shift.

Answer 27

This means that this tissue is likely prospective mesoderm. (indeed it is).

Question 28

How are cells which ingress guided in the sea urchin embryo?

Answer 28

They are guided using filopodia and blastocoel extracellular matrix.

Question 29

What allows the extension of the initial invagination into a full archenteron?

Answer 29

In general, extension will be performed via intercalation. This is not an exception, intercalation (convergent extension) causes the extension of the archenteron.

Question 30

What allows the cells to perform apical invagination in a sea urchin?

Answer 30

Invagination is mediated of course by apical constriction, and apical constriction requires a transcellular cytoskeleton network (essentially the cells must be able to pull on something or constrict something), they do this to the ECM.

Question 31

How does invagination of the neural fold occur?

Answer 31

It also relies on apical constriction. It also involves utilization of the of to more points of apical constriction, this makes allows the neural furrow to form an actual tub. actin mediated adhesion is often seen in apical constriction as it is so dynamic of a system.

Question 32

What is involved in a epithelial to mesenchymal shift? (at least in the sea urchin?)

Answer 32

These cells will endocytose their cadherin molecules, this allows them to no longer strictly adhere to the each other. They down catenin expression (which further destabilizes adherins). The cells will then actively extend cell processes towards the blastocoel (filopodia)

Question 33

Which to mechanism are decreasing adhesion

Answer 33

Endocytosis of cadherins.

Down regulation of catenins

Question 34

Slug, Snail and Twist upregulation is assocaited with what?

Answer 34

Slug, Snail, and Twist, everything awful in this world are assocaited with an epithelial to mesenchymal shift. This is because transcription factors like snail, slug, and twist are so ugly, you want to hide in the center of whatever body cavity you happen to be apart of.

Question 35

Snail, Slug, and Twist are the transcription factors which initiate the majority of mesenchymal to epithelial shifts.

Answer 35

This is dang true.

Question 36

Note, that when we see ingression of the primitive streak, what do we see fading away? Correlate this with what you know about apical constriction?

Answer 36

We see the degredation of the basal layer (an transcellular ECM at the bottom of the cell), we see the same things in upper cells, though this may be correlated to gap junction in the upper cells.

Question 37

What is another time we see ingression of cells? Hint: it is when we see the neural crest ingress after formation of the neural tube. Give it some significance John.

Answer 37

Two tings, well things…
One this shows another time where ingression and invagination are working in conjunction. Two It shows taht this is an important process as the neural crest gives rise to many significant tissue types.

Question 38

We discussed mesenchymal filopodia, what are they up to?

Answer 38

They are locating concentration gradients, and being guided towards or away from the source of the gradient. This allows them to have specific targets when they migrate.

Question 39

What is pathway guidance?

Answer 39

Pathway guidance involves a migrating mesenchymal cell following fixed markers in a path (Perhaps signals in the ECM) in order to find a location.

Question 40

In addition to guiding mesoderm in the first m->e transition. What other purpose will filopodia have to play?

Answer 40

Filopodia will use pathway guidance to guide the archenteron to its target, the future mouth.

Question 41

In the case of pathway guidance as used by the archenteron as it tries to find the site of the prospective mouth…

Answer 41

The archenteron utilizing pathway guidance will send out filopodia. These filopodia will attach to sites around the blastocoel, they will attach the longest to sites where the prospective mouth will form. The archenteron can be pulled towards this source, it may even be a gradient in the blastocoel wall. We will see longer attachment where sites have stronger adhesion, which will pull us differentially towards said sites, this in turn will result in more attachments being made to this site, as it is closer to the source of the filopodia, which will cause it to be pulled more strongly towards it, and we continue this positive feedback loop until we have attachment. Pathway guidance.

Question 42

Pathway guidance defines two possible routes for the neural crest to travel, this type of guidance involves both inhibitory signaling, and attractive signaling.

Answer 42

This is true.

Question 43

Convergent extension works by means of

Answer 43

Intercalation.

Question 44

What will be the result of medio-lateral intercalation?

Answer 44

Medial lateral intercalation will result in the elongation of a structure.

Question 45

Germ band extension is also driven by a medio-lateral extension. The germ-band is the region which in drosophilia surges upwards, and then relaxes, this is what we see prior to segmentation.

Answer 45

I may be wrong about this, regardless, the germ band and the archenteron are two examples of intercalation driving convergent extension (they converge, and therefore extend)

Question 46

Intercalation will require remodeling of junctions, how is this achieved.

Answer 46

Old existing junction will be dismantled and new junctions will be made.

Question 47

Cells will also use hydrostatic pressure to extend and stiffen a structure. Give an example

Answer 47

We see this in the stiffening of the notochord. For this to work as means of extension a structure must be strong across its circumference but week across its length.

Question 48

How can you create hydrostatic pressure in a cavity?

Answer 48

You can create hydrostatic pressure by pumping the cavity full of na+ (or any electrolyte and letting water follow by passive movement), this will result in an increase of water pressure, and expansion of yours structure (if it is much strong in the circumference then on the two ends (weak longitudinally)

Question 49

What is directed dilation?

Answer 49

Directed dilation is the wrapping cords of microtubules, which (in plants) will correspond to cords of cellulose microfibrils, which cause there to be only one direction in which hydrostatic pressure can expand the now tube only one direction. Therefore we see specific growth patterns.