Vetebrate Pattern Development (L28, 29, 30)

Question 1

Blastomere

Answer 1

Cell produced by cleavage

Question 2

Blastoderm

Answer 2

Forms at animal pole.
Yolk prevents blastoderm formation.
Eventually engulfs yolk and forms embryo.

Question 3

Blastocyst

Answer 3

Formed in development of mammals.
ICM (inner cell mass) becomes embryo.
Trophectoderm becomes placenta.

Question 4

Inner Cell Mass

Answer 4

Becomes embryo, part of blastocyst

Question 5

Trophectoderm

Answer 5

Becomes placenta, part of blastocyst

Question 6

Ectoderm

Answer 6

Animal cap region.

Question 7

Mesoderm

Answer 7

Between animal cap and vegetal regions.

Question 8

Endoderm

Answer 8

Vegetal region.

Question 9

Animal-Vegetal Axis

Answer 9

Different concentration of maternal determinants along axis.

Question 10

Vg1

Answer 10

TGF-beta family of growth factors.

Vegetal mRNA.

Question 11

Veg-T

Answer 11

transcription factor.
Vegetal mRNA.
Induce mesoderm via Xnr5, Xnr6, Derrière.
Induces nodal (dorsal mesoderm induction)

Question 12

XWnt11

Answer 12

Vegetal mRNA.

Moves dorsal due to cortical rotation.

Question 13

Grey Crescent

Answer 13

D-V axis formation.
Mixing of vegetal and animal cytoplasm.
Dorsal, opposite sperm entry point.

Question 14

Wnt/B-catenin Signalling

Answer 14

Components move dorsally due to cortical rotation.
Activation: B-catenin in nuclei of dorsal blastomeres.
B-catenin injection can induce ventral to dorsal and induce new body axis/nervous system (like organiser)

Question 15

Cortical Rotation

Answer 15

Movement of maternal determinants signals zygotic gene expression via wnt/B-catenin signaling.

Question 16

Nieuwkoop Centre

Answer 16

B catenin in vegetal cells (xenopus).

Lots of nodal.

Question 17

Chick D-V axis

Answer 17

Due to gravity.
Asymmetric distribution of maternal determinants due to rotation.
Posterior marginal zone cells form at highest point of tilted blastoderm (Wnt8c and Vg1)- dorsal
PMZ leads to formation of primitive streak – gastrulation and anterior-posterior axis

Question 18

Dorsal Mesoderm

Answer 18

Notochord, Neural tube, Muscle

Question 19

Ventral Mesoderm

Answer 19

Epidermis, Blood, Mesenchyme

Question 20

Xnr5, Xnr6, Derrière

Answer 20

Nodal-related proteins.
TGF family.
Induce mesoderm.
Earliest zygotic genes expressed in vegetal cells. 
Rely on VegT.

Question 21

BMP Signals (TGF)

Answer 21

Smad 1, 5, 8.
Ventralise mesoderm.
Only work after mesoderm induction.
Low BMP in trunk.
Notochord-derived BMP antagonists induce neural tube (neurulation)
Deplete BMP, all ectoderm is neural tissue (neural tissue is default)

Question 22

Nodal/Activin Signals (TGF)

Answer 22

Smad 2, 3.

Induce dorsal mesoderm.

Question 23

Nodal

Answer 23

Induce dorsal mesoderm.
Inhibit Fox1e.
Induce spemann organiser.

Question 24

Ectodermin

Answer 24

Maternal.
Gradient inhibits mesoderm induction.
Ubiquitin ligase –targets Smad4.
Animal cap cells.

Question 25

Foxl1e

Answer 25

Zygotic. Specifies ectoderm –epidermis and stops ‘mixing’. Inhibited by nodals.

Question 26

Spemann Organiser

Answer 26

Graft of dorsal blastopore lip induce a new body axis including nervous system. Induced by high Nodal from Nieuwkoop Centre. Differentiates into dorsal mesoderm (eg. notochord) Dorsalizes surrounding mesoderm to from paraxialmesoderm (somites) Dorsalizes ectoderm → neural tube formation (Neurulation) Initiates gastrulation movements (A-P axis)

Question 27

Involution

Answer 27

* Rolling in mesoderm, endoderm * Apical cell constriction (bottle cells) * Involution of migratory cells (subsurface) and pulling in of superficial cells (bottle) * Cell migration along roof of blastocoel, form archenteron (archenteron forms GIT) * Roof of archenteron is bottle cells * Endomesoderm migrates, convergent extension

Question 28

Convergent Extension

Answer 28

* Mesoderm * Medio lateral intercalation * Directional, narrow along one axis, extend along another * Cells converge on primitive streak

Question 29

Epiboly

Answer 29

* Ectoderm * Radial intercalation (multilayered epithelium to single layer, more SA) * Cell proliferation * Multidirectional cell movement

Question 30

Blastocoel

Answer 30

Blastocyst cavity. First cell cavity.

Question 31

Archentron

Answer 31

Forms during involution. | Primitive gut.

Question 32

Blastopore

Answer 32

Opening in archentron. | Forms mouth or anus.

Question 33

Wnt/PCP (planer cell polarity) Signalling

Answer 33

Convergent extension. (not B-catenin) Via DEP and PDZ domains of disheveled. RhoA (GTPase) acts on Jnk cascade and Actin cytoskeleton to cause PCP. Mutations disrupt convergent extension and epiboly, can't extend A-P axis. Antagonistic to Wnt/B-catenin

Question 34

Silberblick (slb)

Answer 34

``` wnt11 mutant (wnt/PCP signaling) def6 knockdown worsens phenotype. ```

Question 35

Pipetail (ppt)

Answer 35

``` wnt5 mutant (wnt/PCP signaling) Rescued by def6 injection. ```

Question 36

def6

Answer 36

Expressed during epiboly. Injection can rescue wnt5 mutants (functions downstream of wnt) Knockdown worsens wnt11 mutant phenotype. Activates RhoA. (Wnt/PCP) by acting as RhoGEF

Question 37

Early organiser

Answer 37

``` Induce head structures. Mesendoderm. Expresses Frzb (Wnt antagonist) Low Wnt in head. ```

Question 38

Late Organiser

Answer 38

Induce tail structures. Notochord. Express chordin (BMP antagonist) High Wnt in tail.

Question 39

Wnt/BMP antagonists

Answer 39

XWnt8 and BMPs ventralise mesoderm Chordin: antagonise BMP, expressed by late/trunk organiser. Frzb: antagonise Wnt, expressed by early/head organiser.

Question 40

Hox Genes

Answer 40

Acitvated by posterior-anterior gradients of Wnt, BMP, FGF, retinoic acid. Activated via CDX.

Question 41

PitX2

Answer 41

Transcription Factor. | Heart looping, expressed on LHS.

Question 42

LHS Patterning

Answer 42

Notch signalling and nodal expression. (Ca2+ release) shh/Nodal signalling. Shh/BMP → Nodal→Pitx2

Question 43

RHS Patterning

Answer 43

Activin signalling. BMP/Activin → FGF Antagonizes Shh

Question 44

Lefty

Answer 44

Maintains L-R boundary