Lecture 2 - Vertebrates from egg to embryo

Question 1

What makes an animal a vertebrate?

Answer 1

has a head, dorsal nerve chord & notochord

notochord = precursor to modern day vertebrate

Question 2

Describe the similarity/differences in early embryonic development in vertebrates

Answer 2

SIMILARITIES
- once a level of polarity

DIFFERENCES
- oocytes if different sizes
- formation of an embryo is very different

Question 3

What stage of embryonic development is consistent between vertebrates?

Answer 3

phargyngula stage

Question 4

What highly repeated structures were observed by Haeckel?

Answer 4

• vertebrates tend to have 5-9 pharyngeal pouches
• somites are also repeated
• meta metric structures - repeated modules - SEGREGATIO

Question 5

What is likely to have caused the similarities in development in vertebrates?

Answer 5

a ‘bottle-neck’ during developmemnt that are evolutionarily conserved

Question 6

What occurs after the sperm meets the egg?

Answer 6

cleavage (division) occurs synchronously

Question 7

What is the name given to cells when dividing?

Answer 7

blastomeres

Question 8

What occurs during the blastula stage?

Answer 8

• cells are on the outside of the inside cavity

Question 9

What is the name given to cells on the exterior during the blastula?

Answer 9

blastoderm

Question 10

What is the name given to cells in the cavity during the blastula stage?

Answer 10

blastocoel

Question 11

How often do cells in the embryo tend to divide?

Answer 11

Every 30 minutes

Question 12

What is the equation to work out the number of cells in early cell proliferation?

Answer 12

N(start) x 2^(txf) = N finish

N = number of cells
t = time
f = frequency

Question 13

What occurs directly after sperm entry?

Answer 13

a wave of free Ca2+ (calcium) ion travel across the egg.

Question 14

What is the purpose of the wave of calcium after sperm entry?

Answer 14

• allows development to proceed, as calcium acts on proteins that controls the cell cycle to initiate cleavage (cell division)

Question 15

What occurs to ensure that cell division is synchronised?

Answer 15

• oscillations in Ca2+ levels during early development.
• small release of calcium before divisions where cleavage is occurring

Question 16

What stages are there in the cell cycle in the early embryo?

Answer 16

“rapid synchronous cleavage”

• S&M phase only, no G phase

Question 17

What process is suppressed in the cell cycle in the early embryo?

Answer 17

transcription

Question 18

What provides the building blocks for DNA synthesis & growth?

Answer 18

maternal store (RNA & protein)

Question 19

What occurs in the S stage?

Answer 19

synthesis - DNA replication

Question 20

What occurs in the M stage?

Answer 20

mitosis - nuclear division
cytokinesis - cytoplasmic division

Question 21

Describe what happens to the maternal RNA & zygotic RNA levels after zygotic genome activation

Answer 21

after zygotic genome activation, maternal RNA falls, with zygotic RNAs rising

Question 22

What are the characteristics of zygotic genome activation?

Answer 22

• cell cycle slows
• cell cycle becomes asynchronous
• cell movement begins

Question 23

When does zygotic genome activation occur in a mouse?

Answer 23

2-cell stage

Question 24

When does zygotic genome activation occur in a frog?

Answer 24

5,000-cell stage

Question 25

What occurs during gastrulation?

Answer 25

formation of the 3 germ layers: - ectoderm (outside) - mesoderm - endoderm (involves the complex rearrangement of tissues)

Question 26

How do the endoderm & mesoderm form?

Answer 26

movement of cells to the inside of the embryo

Question 27

How does the ectoderm form?

Answer 27

the cells that remain on the surface of the embryo form the ectoderm

Question 28

What axis are established as a result of gastrulation?

Answer 28

establishment of true dorsal/ventral axes

Question 29

What are the derivatives of the ectoderm?

Answer 29

- neurones - glia - epidermis - pigment cells

Question 30

What are the derivatives of the mesoderm?

Answer 30

- muscle - cartilage, bone - dermis - kidney - heart - blood

Question 31

What are the derivatives of the endoderm?

Answer 31

- gut - lungs - associated organs

Question 32

What are the epithelial cells like in the first tissue?

Answer 32

structured & tend to be cuboidal. They can migrate but usually come together as a sheet or cluster

Question 33

What are mesenchymal cells like in the first tissue?

Answer 33

move easily and are amorphous (no defined shape)

Question 34

What can be said about mesenchymal cells that are held tight together?

Answer 34

they have undergone condensation

Question 35

What can epithelial cells turn into?

Answer 35

mesenchymal cells (and visa versa)

Question 36

What are the forces that drive cell & tissue rearrangements?

Answer 36

cytoskeletal rearrangement occurs as a result of a change in the expression of cell surface proteins (cell adhesion molecules)

Question 37

What are the different types of cytoskeletal rearrangements that can occurs as a result of a change in the expression of cell surface proteins?

Answer 37

- migration - localised cell proliferation - cell death

Question 38

What is morphogenesis?

Answer 38

The creation of shape

Question 39

What are the stages of embryonic development in a zebrafish?

Answer 39

early cleavage --> cleavage --> somitogenesis

Question 40

What do somites form in zebrafish?

Answer 40

- anterior to posterior - form on either side of the neural tube

Question 41

What is underneath the neural tube?

Answer 41

notochord (precursor of vertebrate)

Question 42

Where & when do somites form?

Answer 42

form following gastrulation in the mesoderm

Question 43

Where do mesenchymal cells gather towards the end of gastrulation?

Answer 43

dorsally

Question 44

What leads to the segmentation of different structures in the adult?

Answer 44

is the result of segmentation during somitogenesis

Question 45

What are the 2 mesodermal progenitors in the somite?

Answer 45

Dermomyotome - dermis & skeletal muscles Sclerotome - vertebrae & ribs

Question 46

How many vertebrae does one somite give rise to?

Answer 46

2 halves of a vertebrae

Question 47

How is it that trunk muscles are also segmented?

Answer 47

this occurs as we maintain muscle segmentation in an adult

Question 48

What is the neural tube composed of?

Answer 48

brain & spinal cord

Question 49

Where does the neural tube arise from?

Answer 49

ectoderm

Question 50

What is the name given to the process by which the neural tube is formed?

Answer 50

neurulation