Developmental biology

Question 1

What is the purpose of cleavage divisions?

Answer 1

Can set up asymmetries by segregating determinants

Question 2

What is pattern formation?

Answer 2

The process by which a spatial and temporal pattern of cellular activities is organised within the embryo so that a well-ordered structure develops

Question 3

What structures arise from the endoderm?

Answer 3

Gut, liver, lungs

Question 4

What structures arise from the mesoderm?

Answer 4

skeleton, muscle, kidneys, heart , blood

Question 5

What structures arise from the ectoderm?

Answer 5

epidermis of skin, nervous system

Question 6

What processes are involved in morphogenesis?

Answer 6

• differential proliferation
• change in cell shape and size
• cell movement
• cell fusion
• cell death
• gastrulation - moves the germ layers relative to one another

Question 7

What are blastomeres?

Answer 7

• produced by cleavage
• divisions occur in the absence of growth
• spherical blastomeres form a loose clump

Question 8

Describe the formation of the morula

Answer 8

• E-cadherin becomes restricted to regions of intercellular contact
• increased cell-cell adhesion maximises contact between blastomeres, forming a compact ball of cells held together by tight junctions

Question 9

What is the result of tangential cleavages?

Answer 9

• produce one polarised and one nonpolarised daughter cell
• outer cells have distinct apical and basal surfaces
• the nonpolarised cells form the inner cell mass
• the inner cells communicate extensively through gap junctions

Question 10

What is the difference between apical and basal surfaces?

Answer 10

The apical surface is the exterior surface and has microvilli.
The basal/basolateral surface is the internal surfaces and contains E-cadherin

Question 11

List the 2 lineages that the outer and inner cells give rise to

Answer 11

trophectoderm and inner cell mass (ICM)

Question 12

List the features of a blastocyst

Answer 12

1. the inner cell mass will give rise to the embryo proper
2. the zona pellucida prevents implantation in the oviduct
3. flattened epithelial cells of the trophectoderm will form extra-embryonic tissues
4. fluid-filled blastocyst cavity (blastocoel)

Question 13

How does fluid accumulate in the blastocoel?

Answer 13

• tight junctions between outer cells act as a permeability barrier
• sodium ions are actively transported into the blastocoel
• as the ion concentration in the blastocoel increases, water flows in by osmosis
• the resulting hydrostatic pressure inflates the blastocoel

Question 14

Describe human development from fertilisation to day 6

Answer 14

• implantation requires interactions between trophoblast integrins and laminin and fibronectin extracellular matrix protein expressed by the epithelial cells of the uterine mucosa
• the inner cell mass is now called embryoblast

Question 15

Describe the fates of the epiblast and the hypoblast

Answer 15

epiblast:
- columnar cells adjacent to newly formed amniotic cavity
- will form the embryo proper

hypoblast:
- small cuboidal cells adjacent to the blastocyst cavity
- will form extra-embryonic structures that will connect to the mother’s circulation

Question 16

What is the primitive streak?

Answer 16

• forms after two weeks on the surface of the epiblast in the region that will become the posterior of the embryo
• the first sign of anteroposterior axis
• during gastrulation, epiblast cells migrate towards the primitive streak and invaginate, displacing the hypoblast

Question 17

List the order of invagination of the three germ layers

Answer 17

• the endoderm
• the mesoderm
• the ectoderm

Question 18

Describe the formation of the neural tube

Answer 18

• the ectoderm folds along its central axis
• the neural folds elevate and fuse
• neural crest cells form near the site of fusion and migrate away
• the epidermis fuses above the neural tube

Question 19

What are somites?

Answer 19

• formed from the paraxial mesoderm
• generate trunk and limb muscles, dermis and vertebrae

Question 20

List the common stages of development

Answer 20

1. fertilisation
2. cleavage to form the blastula
3. gastrulation to reorganise the structure of the embryo and generate the germ layers
4. neurulation
5. organogenesis

Question 21

What does genomic equivalence suggest?

Answer 21

Somatic cell nuclear transfer shows that almost all somatic cells have a complete copy of the genome –> a differentiated cell’s nucleus can direct development of a new individual, providing it has not lost any of its genetic potential

Question 22

List some model organisms

Answer 22

• mouse
• zebrafish
• drosophila melanogaster
• frog - xenopus laevis
• nematode worm
• chick

Question 23

What is significant about xenopus eggs?

Answer 23

they have visible and molecular polarity

Question 24

What is the purpose of VegT?

Answer 24

VegT binds DNA and activates expression of:
- transcription factors that mediate endoderm differentiation
- nodal TGFB signalling factors that are secreted and induce responding cells to from mesoderm

Question 25

What is the evidence for VegT's function

Answer 25

- VegT mRNA and protein can be detected in the cells that will give rise to endoderm - removing VegT from the oocyte interferes with both endoderm development and mesoderm induction - VefT expression in the ectoderm results in expression of endoderm-specific genes

Question 26

Describe the Wnt signalling cascade

Answer 26

- when Wnt is absent GSK-3B destroys B-catenin in the vegetal region - after cortical rotation, the dorsal determinants activate Wnt signalling and inhibit GSK-3 on the future dorsal side - B-catenin is stabilised and enters nuclei on the dorsal side - ventral nucleui do not receive B-catenin

Question 27

What is cortical rotation and what is its purpose?

Answer 27

- activated by sperm entry - redistributes determinants including Wnt11 and inhibitory GSK-3-binding protein to the prospective dorsal side, where they activate the Wnt signalling pathway

Question 28

What is the purpose of B-catenin?

Answer 28

Required for normal development of dorsal axial structures

Question 29

Describe how B-catenin activates expression of goosecoid

Answer 29

- B-catenin interacts with Tcf-3 to activate expression of siamois - siamois (acting synergistically with proteins induced by nodal signalling) activates expression of goosecoid

Question 30

Describe the result of nodal expression activated by VegT and B-catenin

Answer 30

- high nodal plus B-catenin induces dorsal mesoderm - low nodal induces ventral mesoderm

Question 31

What do somites differentiate into?

Answer 31

muscle

Question 32

What would be the result of grafting dorsal organiser cells to the ventral side of a host?

Answer 32

a secondary axis complete with head and nervous system

Question 33

What are myoblasts?

Answer 33

cells that express MyoD (a muscle-inducing transcription factor) and differentiate into skeletal muscle

Question 34

What is the result of over-expression of MyoD

Answer 34

can convert non-muscle cells into muscle cells