Lecture 6: building embryos

Question 1

Building embryos pathway:

Answer 1

-Zygote
-Blastocyst
–>PSCs –> different cell types
OR –> post-implantation epiblast –> Gastrulations etc

Question 2

Central problem with building embryos

Answer 2

transition from single cell zygote to a complex organism is complex

Question 3

what processed does building an embryo involve?

Answer 3

• cleavage
• pattern formation
• morphogenesis
• Growth
• cell differentiation

These processed are not ness. sequential and not independent

Question 4

cleavage:

Answer 4

cell division without increase in cell mass

Question 5

Pattern formation:

Answer 5

laying down the spatio-temporal pattern in an embryo

Question 6

morphogenesis

Answer 6

major changes in 3d for of an embryo

Question 7

cell differentiation

Answer 7

process whereby cells become structurally and functionally different

Question 8

primordial germ cells are from

Answer 8

the proximal epiblast

Question 9

early mouse development:

Answer 9

• one cell
• two cell
• eight cell (non-compacted)
• Early morula. (eight cell, compacted)
• Morula is where the first changes become apparent. Cells on the outside become different to those on the inside
• Embryonic stem cells come from the epiblast
• Cells taken from an early blastocyst are manipulated to try and make them mimic what happens in an epiblast
• Mouse development different to primates

Question 10

early mouse development: inner cells –>

Answer 10

inner cells –> epiblast ( a subset) –> Embryo

Question 11

early mouse development: outer cells –>

Answer 11

extra-embryonic (placenta)

Question 12

early mouse development gastrulation:

Answer 12

produces 3 germ layers.

• ectoderm: skin, nervous system
• mesoderm: muscle, heart, blood
• endoderm: gut lining, liver, pancreas

Question 13

early mouse development: the node gets ___ anterior as the primitive streak extends anteriorly

Answer 13

more

-the head form anterior to the node and notochord

Question 14

early mouse development: epiblast cells migrate through

Answer 14

the primitive streak.

-emerge as mesoderm and endoderm

Question 15

gastrulation from a flat bilaminar disc -chicken

Answer 15

• Cells involute through primitive streak
• Cells laminate out and displace hyperblasts to the sides
• Neural tube, somites and notochord are formed from above Henson’s node
• Primitive streak forms the mesoderm and endoderm

Question 16

what is the key to patterning the germ layers

Answer 16

signalling

Question 17

what are the four main signalling centres

Answer 17

1) post. epiblast
2) Anterior Visceral Endoderm (AVE)
3) Extra-embryonic endoderm
4) The Node

Question 18

signalling: BMP4

Answer 18

Gradient of BMP4 
-Bmp4 induced Nodal in EPIBLAST
-Nodal induces Lefty1 in DVE
-Lefty1 gradient restrict Nodal
-Note: Bmp4 inhibits any Lefty1 in visceral endoderm
LEFTY 1 gets restricted to the DVE

Question 19

DVE =

Answer 19

Distal Visceral Endoderm

Question 20

as embryo grows- AVE + DVE pushed …

Answer 20

anteriorly
-Gradient of DKK1from DVE inhibits Wnt
Gradient of Lefty1 from DVE and AVE inhibits Nodal
NET effect: WNT and TGFb signals restricted to posterior epiblast
-Wnt and TGFb signals set up Primitive streak
-Primitive streak starts to elongate
-Node (highest Nodal expression) is where the notochord will start to form

Question 21

how does the embryology relate to differentiation of pluripotent stem cells

Answer 21

you have to mimic the timing, concentration and ideally the position of these signals

Question 22

formation of the anterior (head) neural structures:

Answer 22

epiblast on top, hypoblast on bottom.
anterior end AVE forms with rural plate behind. Posterior end - primitive streak forms with node in centre of complex. non-neural ectoderm surrounding rest

Question 23

neurulation:

Answer 23

neural plate folds o give the neural tube tube

Question 24

somites:

Answer 24

sclerotomes, myotomes and dermatomes vertebrae , rib cage, skeletal muscle, cartilage, tendons, and skin.

Question 25

rhombomeres

Answer 25

form the brain

Question 26

high FGF signalling at the posterior end keeps cells

Answer 26

in a proliferating state

Question 27

FGF and RA give cells

Answer 27

posterior identity

Question 28

Anti-Wnts maintain

Answer 28

anterior identities

Question 29

signals: Remember in the epiblast:

Answer 29

• The WNT and TGFbeta signals have to be RESTRICTED to the POSTERIOR side of the EPIBLAST if you want tissues derived from PRIMITIVE STREAK.
• Bmp4 induces Lefty1(restricts NODAL) and Wnt
• Wnt induces Nodal (TGFb) which inhibits Lefty1.
• Without these signals – ectoderm.

Question 30

in an ES cell: For primitive streak

Answer 30

use Wnt, Activin (TGFb)

Question 31

in an ES cell: for ectoderm:

Answer 31

BLOCK TGFb and BMP signals

Question 32

ectoderm patterning: At the head end (anterior) of the embryo:

Answer 32

• FGFs needed for proliferation

- BMP decides what sort of ectoderm (AP axis)

Question 33

ectoderm patterning in an ES cell

Answer 33

FGF with no BMP added to drive neural drift

Question 34

the initial germ layer specification of an embryo is a complex combination of

Answer 34

Growth,patterning, morphogenesis and differentiation

Question 35

the embryo relies on ____ signals and gradients to

Answer 35

positive and negative

-restrict gene expression (ie pattern). This leads to differentiation

Question 36

lessons from embryology teach us how

Answer 36

to trigger differentiation along lineages we want