Forming Embryonic Axes

Question 1

What is important in establishing the AP axis in avian embryos like chick embryos?

Answer 1

Gravity

Question 2

How many times does the egg spin in the hen?

Answer 2

10-15 times/hour for 20 hours

Question 3

What lies under one side of the blastoderm of a chick?

Answer 3

Lighter yolk components

Question 4

Where does the primitive streak in chick embryos form?

Answer 4

Posterior and extends anteriorly

Question 5

Can each wedge of the cut chick embryo form its own primitive streak?

Answer 5

Yes

Question 6

What molecule is important for primitive streak formation?

Answer 6

Vg1

Question 7

What experiment was done to observe the expression of cNodal in the primitive streak?

Answer 7

Transplant cells expressing Vg1 at the opposite side of the embryo from Koller’s sickle
Allow embryos to develop until the primitive streak is formed
Perform whole mount in situ hybridization experiment to monitor expression of cNodal

Question 8

If Vg1 pellet is placed at the anterior end, what happens?

Answer 8

Ectopic and endogenous primitive streaks form

Question 9

If Vg-1 pellet is placed on lateral margin, what happens?

Answer 9

Only ectopic primitive streak forms
Formation of endogenous primitive streak is inhibited

Question 10

What happens if 2 Vg-1 pellets are implanted?

Answer 10

Only one primitive streak forms

Question 11

What was suggested from the observation of one primitive streak forming in the presence of two Vg-1 pellets?

Answer 11

Vg-1 induces both the primitive streak and the expression of a molecule that inhibits induction of the other primitive streak

Question 12

What is the first definitive axis in the mouse embryo?

Answer 12

AP axis

Question 13

What are the signaling centers required to pattern the anterior end of the mouse embryo?

Answer 13

Node (organizer) and anterior visceral endoderm (AVE)

Question 14

Where is AVE derived from?

Answer 14

Distal visceral endoderm (DVE)

Question 15

The position of AVE is determined by what?

Answer 15

Physical constraints of uterus

Question 16

Primitive streak and node form on ___________ side of the embryo from AVE

Answer 16

Opposite

Question 17

There are (high/low) levels of Nodal in distal epiblast and (high/low) levels of Nodal in proximal epiblast of the mouse embryo

Answer 17

Low; high

Question 18

What is required for patterning the anterior end of the embryo?

Answer 18

AVE

Question 19

What is node responsible for?

Answer 19

Creating the body plan

Question 20

Where are 3’ and 5’ genes more expressed in Hox gene clusters?

Answer 20

3’ genes more anteriorly and 5’ genes more posteriorly

Question 21

What do mutations in Hox genes cause?

Answer 21

Homeotic transformations

Question 22

Loss-of-function mutations in Hox genes cause _____________ to ______________ transformations

Answer 22

Posterior; anterior

Question 23

Gain-of-function mutations in Hox genes cause _______________ to ________________ transformations

Answer 23

Anterior; posterior

Question 24

How many clusters of Hox genes do vertebrates have?

Answer 24

Four

Question 25

What left-right asymmetry is associated with the heart on the left, left lung bilobed and right lung trilobed, liver on the right, stomach and spleen on the left?

Answer 25

Situs solitus

Question 26

What kind of asymmetry is typically inherited?

Answer 26

Directional asymmetry

Question 27

What is the first step in LR patterning?

Answer 27

Initiation

Question 28

When does initiation occur?

Answer 28

Prior to node formation and at the level of the node

Question 29

What is another critical early step in establishing LR axis?

Answer 29

Asymmetric cell movement at Hensen's node

Question 30

Which molecules of Hensen's node drive asymmetric gene expression in chicks?

Answer 30

Shh on the left and Cldn10 on the right

Question 31

What is found at the node of mouse, rabbit, zebrafish and Xenopus?

Answer 31

Cilia

Question 32

What happens if Kif3B is knocked out in embryos?

Answer 32

LR patterning defects, stunted and immotile cilia

Question 33

True or false: Monociliary movement is important for left-right patterning

Answer 33

True

Question 34

What is the second step in LR patterning?

Answer 34

Stabilization of the signal

Question 35

What are the events of the second step?

Answer 35

Asymmetric expression of nodal in chick (at the node and/or in the perinodal region)

Question 36

What is the third step of LR patterning?

Answer 36

Propagation of signal

Question 37

What are the events of the third step?

Answer 37

Transfer and maintenance of information on left and right sides of the embryo Midline (Notochord) acts as a barrier Asymmetric gene expression turned on (Lateral plate mesoderm LPM)

Question 38

In chick, Nodal is expressed on which side of the perinodal region?

Answer 38

Left

Question 39

What is the purpose of Lefty?

Answer 39

Feedback inhibitor of Nodal signaling

Question 40

The diffusion model that hypothesizes that interactions between an activator and an inhibitor control signaling gradients within a field of cells and subsequently pattern them is referred to as what?

Answer 40

The Turing reaction

Question 41

What are the principles of the reaction-diffusion model?

Answer 41

Activator activates its own production Activator activates its inhibitor Inhibitor blocks autoactivation of the activator Inhibitor acts at a long range to restrict the effective range of the activator

Question 42

Asymmetric Pitx2 expression occurs on which side of the LPM?

Answer 42

Left side

Question 43

Asymmetric Pitx2 expression is induced by what signaling pathway?

Answer 43

Nodal

Question 44

Bilateral Pitx2 expression randomizes the direction of heart looping in which organisms?

Answer 44

Chick and Xenopus

Question 45

What is the fourth step of LR patterning?

Answer 45

Translation of signal

Question 46

Where does the translation of signal occur?

Answer 46

Along the entire AP axis and at the level of individual organs

Question 47

What event occurs during the fourth step?

Answer 47

Pitx2 is asymmetrically expressed in organs that exhibit asymmetry

Question 48

Which steps are species-specific or conserved in all species?

Answer 48

Steps 1 and 2 are species-specific and steps 3 and 4 are conserved in all species

Question 49

What is the cellular basis of asymmetric organogenesis?

Answer 49

Differential cell death, differential proliferation, differential cell elongation, differential migration, rearrangement of actin-cytoskeleton, intrinsic/extrinsic forces