Early Invertebrate Development

Question 1

What is autonomous cell fate specification?

Answer 1

A cellular response that can be attributed to a cellular of molecular mechanism occurring within that same cell.

Question 2

What is non-autonomous cell fate specification?

Answer 2

A cellular response that occurs due to the influence of another cell or external factor.

Question 3

What is meant by a “double-negative gate”?

Answer 3

A repressor which acts on a repressor, causing activation.

Question 4

What is the purpose of the Notch signalling pathway?

Answer 4

To promote proliferative signalling during neurogenesis. Regulator of embryonic development.

Question 5

How is nuclear beta-catenin linked to the endomesoderm?

Answer 5

More nuclear beta-catenin = more endomesoderm. Less nuclear beta-catenin = less endomesoderm.

Question 6

What signalling steps follow the activation of Pmar1 by beta-catenin?

Answer 6

Pmar1 represses HesC, stopping repression of Tbr, Delta, Ets, and Dri (double-negative gate).

Question 7

What developmental process is allowed to proceed upon inactivation of HesC?

Answer 7

Skeletogenic diffferentiation by Tbr, Ets, and Dri. Delta activated to stimulate the Notch signalling pathway.

Question 8

What is ChIP? (3 steps)

Answer 8

Chromatin immunoprecipitation.

• Crosslink DNA/protein
• Fragment DNA
• Precipitate DNA of interest with protein-specific antibody

Question 9

What 3 phases describe gastrulation?

Answer 9

1. Mesenchymal cells migrate from endoderm to blastoceal
2. Vegetal plate “invaginates” the blastoceal (=primitive gut)
3. Secondary mesenchyme delaminates and enters blastoceal

Question 10

What is meant by “induction”?

Answer 10

The non-autonomous effect of one cell on other cells during development.

Question 11

In the Wnt signalling pathway, what occurs in the absence of Wnt?

Answer 11

Ubiquitin-mediated proteosome degradation.

Question 12

What main feature differentiates gastrulation in deuterostomes from gastrulation in protostomes?

Answer 12

Deuterostomes: gastrulation begins at anus
Protostomes: gastrulation begins at mouth

Question 13

What is the “imaginal rudiment” in a pluteus?

Answer 13

The very early sea urchin. A pentagonal structure which is nurtured within the pluteus until it matures, becoming an adult sea urchin.

Question 14

What is the “archenteron”?

Answer 14

A primitive gut structure produced by invagination during the sea urchin blastula stage.

Question 15

During sea urchin gastrulation, which cells are responsible for inducing endoderm formation? What do these cells become later in development?

Answer 15

The micromeres become the mesoderm in the sea urchin blastula, but are able to induce endoderm formation.

Question 16

What differentiates a cell which is specified from one which is determined?

Answer 16

Specification: fate is established but can still be influenced by outside factors
Determination: fate of the cell is fixed and unchangeable

Question 17

What element and molecule are crucial for cell adhesion and release?

Answer 17

Cadherin mediates cell-cell adhesion, calcium disrupts.

Question 18

In the sea urchin embryo, what cells are fated to become ectoderm? What about endoderm and mesoderm?

Answer 18

Ectoderm: an1 and an2
Endoderm: veg1 and veg2
Mesoderm: large/small micromeres

Question 19

What tissues are derived from the ectoderm?

Answer 19

Epidermis, CNS, neural crest.

Question 20

What tissues are derived from the mesoderm?

Answer 20

Notochord, bone, blood, muscle, kidney tubules.

Question 21

What tissues are derived from the endoderm?

Answer 21

Digestive tract, thyroid, Respiratory tract, germ cells.

Question 22

What is the purpose of cyclin? When is it active?

Answer 22

Linked to mitosis, required for chromatin condensation and spindle formation.

Question 23

How does radial cleavage differ from displaced radial cleavage?

Answer 23

Identical except in displaced radial cleavage the first horizontal cleavage is not equidistant from the poles.

Question 24

How are cellular processes initiated and regulated in the early embryo given that transcription is not active?

Answer 24

Mainly through phosphorylation, also proteolytic cleavage.

Question 25

How can cyclin allow for faster cell division during early development?

Answer 25

By bypassing G1 and G2 phases of cell division.

Question 26

At what stage of the cell cycle do mammalian eggs get arrested prior to fertilization?

Answer 26

Second metaphase.

Question 27

What is Silver-Russell syndrome? What might cause this?

Answer 27

Intra-uterine and postnatal growth restriction, facial dysmorphism, dwarfism. Likely results from the loss of DNA methylation regulating IGF2 and H19.

Question 28

What 2 important regions are imprinted by DNA methylation in human sperm?

Answer 28

The regions which code for the expression of IGF2 and H19.

Question 29

What requires imprinting by methylation to be fully functional? (4 things)

Answer 29

1. Cell proliferation
2. Embryonic/extraembryonic development
3. Fitness
4. Behaviour

Question 30

Are male and female pronuclei equivalent? Why? Why not?

Answer 30

No, mammalian pronuclei are non-equivalent because they each have some of the necessary imprinting (DNA methylation) for development but not all.