Cleavage to Gastrulation... initial commitment and differentiation

Question 1

zygote to trophoblast CELLULAR

Answer 1

• cellular:
• cells of early embryo morphologically identical
• totipotency until 16 cell stage
• innter and outer cells… (inner mass, trophoblast)
• trophoblast (supporting structures, placenta)
• ICM cells pluripotent
• ICM cells = ES cells

Question 2

Early cleavage cells divide..

Answer 2

• symmetrically or asymmetrically
• polar cells (apical and basal surfaces)
• nonpolar cells (inner cells)

Question 3

zygote to trophoblast MOLECULAR

Answer 3

• cells even at 2, 4, 8 cell stage have molecule differences
• noisy gene expression (works itself out)
• regulative ability
• Oct4 key TF
• oct4 in all cells in morula stage, then only in ICM

Question 4

Oct4 expression and function

Answer 4

• development of pluripotent cells in ICM and ES
• essential TF:
  pluripotency maintainance
  cell differentiation
  transdifferentiation
  reprogramming to iPS cells

Question 5

differentiation into trophopblast and ICM

Answer 5

• involves oct4 and Cdx2, reciprocal interation
• see figure

Question 6

What determines if the cell expresses oct4 or cdx2

Answer 6

• something happens to cause differential expression of cdx or oct4

Question 7

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Answer 7

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Question 8

pluripotency network

Answer 8

• formed by TFs oct4, nanog, sox2… up/downregulate to maintain pluripotency

Question 9

ICM to epiblast/hypoblast

Answer 9

• nanog and gata6 orchestrate differentiation to epiblast and hypoblast in the last blastocyst
• turn inner mass into 2 layers
• see figure

Question 10

by the time of implantation

Answer 10

• blastocyst developed:
  epiblast
  primitive endoderm (hypoblast)
  and trophoectodderm (TE)
• extraembryonic tissues are critical to sustain embryonic growth, and pattern embryo

Question 11

multistep model of EPI/PrE lineage formation

Answer 11

• initial expression of TFs is followed by progression towards stabilised salt and pepper pattern of PrE (Gata6) and EPI (Nanog) expression