chick development Flashcards
describe the early cleavages
they are meroblastic and discoidal to form an animal blastodisc. it begins as one layer and then develops into multiple
what happens at 128 days
the zygotic genome is activated. the blastodisc thins around the subgerminal cavity to form the zona pellucida and zona opaca
describe the formation and role of Koller’s sickle
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
what is the role of the primordial streak
cells involute though it. the first cells through become the endoderm and the next cells become the mesoderm
how does Henson’s node from and what is its function
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
what are the equivalents of Koller’s sickle and Hensen’s node
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
when does neurulation begin
when Henson’s node has regressed
describe what happens at ventral closure
it happens anteriorly and posteriorly. the gut tube forms and two bilateral heart rudiments fuse on the midline to from the heart field
describe the roles of the different extraembryonic membranes
amnion is for protection, chorion and allantois for gas exchange and yolk sac for nutrients
what is the role of the maternal determinants
they move to one side of the blastoderm due to yolk revolution. they mark the future posterior and induce the posterior marginal zone
describe the formation of the hypoblasts
the primary hypoblast forms from the joining of hypoblast islands. this is displaced by the secondary hypoblast which grows anteriorly from Koller’s sickle
what is the purpose of the secondary hypoblast
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
how does the germinal crescent form
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
what does the mesoderm from in order, anteriorly to posteriorly
lateral somites, intermediate mesoderm, lateral mesoderm and extraembryonic mesoderm
what is the stem zone and how is it maintained
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
it what ways can turnover be detected (3)
detecting apoptosis proteins, TUNEL assay or detecting phosphatidyl-serine from the membrane
in what ways can proliferation be measured (4)
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
in what ways can new cells be generated (3)
mature cells regaining/retaining their capacity to divide, by mature cells de-differentiating, dividing then re-differentiating or by immature cells dividing and differentiating
what defines a stem cell
immature and undifferentiated cells. they must be capable of division to produce both new stem cells as well as progenitor cells which will differentiate
define pluripotent
can differentiate into all cells of the embryo and germ cells
define totipotent
can differentiate into all cells of the embryo, germ cells and extraembryonic cells
define a precursor
the cell that comes before the cell of interest
define progenitor
a cell that will differentiate. they are generally more proliferative but have a lower self-renewal capacity than stem cells
what is a stem cell niche
a regulatory microenvironment where behaviour to self-renew or differentiate is controlled by local and systematic cues
in what two ways can cell renewal occur
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
what are the problems with stem cell transplants (2)
the transplanted cells aren’t genetically identical so there is risk of rejection. there are also ethical issues due to them ‘killing’ embryos
what are iPSCs
induced pluripotent stem cells. they can give rise to all embryonic cells in vitro but can cause teratomas in adults
