linages of early mammalian embryo Flashcards
explain first 3-4 days of development
very dynamic
development is constrained by the cell wall
volume doesnt change when cell progresses from 1 to many
after compaction rough cell look becomes smooth
the cavity is filled with liquid
what happens after the blastocyst has formed
it emerges from the zona - the zona creates pressure to stop the cells from sticking ( cell division happen in a tight time frame)
what is the cell division pattern important for
the travelling of the embryo from the uterus to the ovary
what happens if the egg doesnt hatch
it falls out and no pregnancy occurs
when is totipotency lost
after the 5th cell division
what is pluripotency
the ability to give rise to somatic cells
how can the 4 cell stage be examined
separation of the blastomeres into 4 dishes to give 4 embryos from this stage - theoretically would produce identical quadruplets
what are the 3 ways linages can be determined
prepatterning model
inside out model
cell polarity model
LEARN DIAGRAMS FROM NOTES
what are the molecular players in the formation of the first lineages in the blastocyst
4 lineage specific transcription factors
Oct4, Cdx2, Nanog and Gata6
when is lineage specific expression established
gradually in association with maturation of cellular structures and of positive and negative interaction amongst the transcription factors themselves
how and where is Oct4 observed
how is it down regulated and when
in all blastomeres throughout early cleavage stages due to maternally encoded proteins
at the 8 cell stage all blastomeres contain oct 4 but it is gradually down regulated in the outer trophectoderm cells by Cdx2 through physical interaction and transcriptional regulation
when is Cdx2 detected
when is it ubiquitous
and where is it restricted
starting from 8-16 cell stage, initial expression is stochastic
by early morula to early blastocysts its expression is ubiquitous and is higher in outer, apically polarised cells
it is restricted in outer TE cells which is established in the blastocyst stage
when is Nanog and Gata6 detected
form 8 cell stage both expressed uniformly until early blastocyst stage
what is nanog down regulated in outer cells by
Cdx2 in a subpopulation of ICM by Grb-2 dependent signalling
what is Gata6 expression maintained by
Grb- 2 dependent signalling
when do cells have to express Nanog or Gata6 exclusively by
by the late blastocyst stage
in the first differentiation event how do oct4, sox2 and nanog regulate eachother
oct4 sox2 and nanog each regulate each other equally
what is cdx2 repressed by in the first differentiation event
oct4 sox2 and nanog and they are repressed by cdx2 - slight imbalance tips production to only one due their mutual inhibitory regulation (small changes accelerate ti become much bigger)
how is cdx2 expressed in 8 cell
asymetrically
what 2 components break the cycle of the first differentiation event
adhesion to other cells of insides cells and outside cells only having adhesion to one side of their cells
what changes the expression of yap protein and what does this regualte
pressure changed expression on YAP - on inside it is cytoplasmic on outside it is nuclear
this regulates the expression of tead4 which regulates cdx2
what decides if cells are inside or outside cells
the position of the cell and its expression of cdx2, more cdx2 = movement to the outside (repositioning can occur)
what is the importance of the apical membrane
the early embryo is very busy, ezrin is localised when cells divide to give an asymmetric shape/distribution this specifies outside fate
the apical membrane is sufficient to initiate fate segregation
what does the second differentiation event rely on
interaction and cross regulation of different transcription factors
in the second differentiation event what reduces nanog
MAPK
in the second differentiation event how are 2 cell populations divided
by being on either side of the basal membrane
what 3 types of cells form the blastocyst
ES cells from the epiblast, XEN cells from the primitive endoderm and TS cells from Trophectoderm
how do cells go from ICM to stem cells
pluripotency, can give rise to all embryonic lineages in vitro and vivo, this is used extensively for the generation of KO mice
TE to trophoblast stem cell lines
this is self renewing and can differentiate into all TE lineages in vitro and vivo and they have appropriate DNA imprints
PrE to extra embryonic ectoderm (XEN) cell lines
gives rise to embryonic endoderm lineages in vitro and vivo
they have peculiar morphology and motility
and have appropriate DNA imprints
Blastocyst derived cell lines
only Es derived from humans
TS cells derived from primates
XEN cells to date are only rodent cells
possibly species differences like in ES
