chick development

Question 1

describe the early cleavages

Answer 1

they are meroblastic and discoidal to form an animal blastodisc. it begins as one layer and then develops into multiple

Question 2

what happens at 128 days

Answer 2

the zygotic genome is activated. the blastodisc thins around the subgerminal cavity to form the zona pellucida and zona opaca

Question 3

describe the formation and role of Koller’s sickle

Answer 3

it forms from the thickening of the tissue at the posterior marginal zone. this extents to form the primitive streak which is a blastopore equivalent

Question 4

what is the role of the primordial streak

Answer 4

cells involute though it. the first cells through become the endoderm and the next cells become the mesoderm

Question 5

how does Henson’s node from and what is its function

Answer 5

it forms at the anterior of the primitive streak. epiblast cells involute though it to from the axial mesendoderm- first the precaudal plate and then the anterior of the notochord which elongates as the node regresses anteriorly

Question 6

what are the equivalents of Koller’s sickle and Hensen’s node

Answer 6

Koller’s sickle is the Nieuwkoop equivalent as it can induce another axis. Henson’s node is the Spemann’s organiser as it can induce another axis and also contributes cells to the axial mesendoderm

Question 7

when does neurulation begin

Answer 7

when Henson’s node has regressed

Question 8

describe what happens at ventral closure

Answer 8

it happens anteriorly and posteriorly. the gut tube forms and two bilateral heart rudiments fuse on the midline to from the heart field

Question 9

describe the roles of the different extraembryonic membranes

Answer 9

amnion is for protection, chorion and allantois for gas exchange and yolk sac for nutrients

Question 10

what is the role of the maternal determinants

Answer 10

they move to one side of the blastoderm due to yolk revolution. they mark the future posterior and induce the posterior marginal zone

Question 11

describe the formation of the hypoblasts

Answer 11

the primary hypoblast forms from the joining of hypoblast islands. this is displaced by the secondary hypoblast which grows anteriorly from Koller’s sickle

Question 12

what is the purpose of the secondary hypoblast

Answer 12

it enables the posterior marginal zone to secrete Veg1 and Wnt8C. this induces nodal expression in the epiblast which promotes formation of the primitive streak and involution of cells

Question 13

how does the germinal crescent form

Answer 13

it is formed when the first endodermal cells involute through the primitive streak displace the hypoblastic cells. they are pushed anteriorly and contain mRNA, such as vasa mRNA, which makes cells precursors to germ cells

Question 14

what does the mesoderm from in order, anteriorly to posteriorly

Answer 14

lateral somites, intermediate mesoderm, lateral mesoderm and extraembryonic mesoderm

Question 15

what is the stem zone and how is it maintained

Answer 15

it is a region lateral and posterior of Henson’s node which has stem cell- like properties which are maintained by Wnt and FGF. when the cells pass through the primitive streak to be said down they stop producing FGF. this prevents the expression of Cyp26 which allows retinoic acid to be produced which promotes differentiation

Question 16

it what ways can turnover be detected (3)

Answer 16

detecting apoptosis proteins, TUNEL assay or detecting phosphatidyl-serine from the membrane

Question 17

in what ways can proliferation be measured (4)

Answer 17

detecting the Ki-67 antigen present in G1/S/G2/M, observing division, detecting PCNA in S phase and incorporating labelled nucleotide analogues into DNA

Question 18

in what ways can new cells be generated (3)

Answer 18

mature cells regaining/retaining their capacity to divide, by mature cells de-differentiating, dividing then re-differentiating or by immature cells dividing and differentiating

Question 19

what defines a stem cell

Answer 19

immature and undifferentiated cells. they must be capable of division to produce both new stem cells as well as progenitor cells which will differentiate

Question 20

define pluripotent

Answer 20

can differentiate into all cells of the embryo and germ cells

Question 21

define totipotent

Answer 21

can differentiate into all cells of the embryo, germ cells and extraembryonic cells

Question 22

define a precursor

Answer 22

the cell that comes before the cell of interest

Question 23

define progenitor

Answer 23

a cell that will differentiate. they are generally more proliferative but have a lower self-renewal capacity than stem cells

Question 24

what is a stem cell niche

Answer 24

a regulatory microenvironment where behaviour to self-renew or differentiate is controlled by local and systematic cues

Question 25

in what two ways can cell renewal occur

Answer 25

cells divide symmetrically with one becoming a stem cell and the other a progenitor, or asymmetrical division where the choice between progenitor and stem cell depends on the environment and relative abundance

Question 26

what are the problems with stem cell transplants (2)

Answer 26

the transplanted cells aren’t genetically identical so there is risk of rejection. there are also ethical issues due to them ‘killing’ embryos

Question 27

what are iPSCs

Answer 27

induced pluripotent stem cells. they can give rise to all embryonic cells in vitro but can cause teratomas in adults