Lecture 9 - Preimplantation Embryonic Development Flashcards
What are the pre-implantation stages?
Fertilisation –> blastocyst
- Oocyte
- Zygote
- 2-cell
- 4-cell
- 8-cell
- Morula
- Blastocyst
What are 4 special features of the pre-implantation stages?
- Surrounded by zona pellucida - cortical granules change the nature of the zona pellucida - hardens it to prevent polyspermy
- Reductive cell cycles - no growth in the actual cell just the nucleus to cytoplasm ratio
- No transcription until 2-cell (mouse) or 4-8-cell (human)
- Cells are all the same and totipotent
What is compaction? When does it occur?
- Happens at 8-cell stage
- Change in microvilli on outside of 8-cell mass (no change on inside)
- Formation of tight (adherens) junctions and E-cadherins between cells on the outside
- Division between apical and basolateral domain
What needs to be required to maintain the tight junctions formed by compaction?
- Ca2+
- ZO1 (zona occludens 1) - no ZO1 = no further development of the embryo past the 8-cell stage
Compaction leads to the formation of 2 cell types - polarised & nonpolarised.
- Radial cleavage of one of the 8-cells results in one ____ cell and one ____ cell.
- Tangential cleavage of one of the 8-cells results in one ____ cell and one ____ cell.
- 2 polarised
2. 1 polarised, 1 nonpolarised
The new polarised and nonpolarised cells created from compaction are ____potent.
Pluripotent - can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent. Can’t give rise to extraembryonic or placental cells (totipotent can).
What transporter allows for the transport of electrolytes and water around the 16-cell stage. Is this transporter found on the apical or basolateral surface?
- Na+-K+-ATPase
- Basolateral surface
What is CAVITATION? What is the cavity filled with?
- Formation of a cavity in the middle of the 32-64cell stage.
- Cavity is filled with salt and water
What cells make up the ICM?
Nonpolarised cells - these are termed the epiblasts (the outermost layer of an embryo before it differentiates into ectoderm and mesoderm)
What cells make up the trophectoderm (outer layer of cells)?
Polarised cells - these are termed trophoblasts
What is one thing that drives the cell lineages (differentiation) of cells?
Transcription factors begin to occur in one cell type and not the other - this further drives their differentiation. Say a cell has the transcription factors A and B. If A is transcribed up to a certain level it inhibits the transcription of B then - can inhibit each other.
The expression of transcription factors is determined by the social context of cells in blastocyst. What does this mean?
Outside cells (trophoblasts) have different social context than inside cells (epiblasts and hypoblasts). Outside (v low cell contact), inside (high cell contact). Thought this low cell contact drives the production of Cdx2, Thought high cell contact turns off signal to produce Cdx2
What are the 2 requirements for blastocyst implantation?
- Adhesion competence
2. Hatching from zona pellucida
What is adhesion competence? What type of signals does the blastocyst rely on to achieve adhesion competence?
- Competence for the blastocyst to be able to adhere to the uterine wall.
- Blastocyst relies on both internal (coming from within the embryo) and external (paracrine, autocrine, juxtacrine, endocrine signalling) signals to do this.
What are 2 hatching mechanisms the blastocyst uses to hatch out of the zona pellucida?
- Rupture: (a) mechanical pressure (caused by cell proliferation & water influx) stretches the zona until it ruptures
(b) chemical digestion by protease secretion helps to degrade the ZP, makes a lil hole in it - Escape: cells of the embryo have actin in them and they start to migrate to cell wall and push against it and out
