2017-2018 SAQ Flashcards
List the 4 mechanism establish and maintain the inner cell mass (ICM) in the blastocyst?
a] What mechanisms establish and maintain the inner cell mass (ICM) in the blastocyst?
- Asymetrical Divisions
- Cell-cell signaling
- Cell adhesion molecules
- Transcriptional regulation
1.Asymmetric cell divisions
a] What mechanisms establish and maintain the inner cell mass (ICM) in the blastocyst?
- Early stages of embryonic development
- fertilised eggs divides several rounds> blastocyst forms
- Some divisions:asymmetric
- > leads to 2 distint cell populations
- 1.trophectoderm
- 2.Inner cell mass
- Asymmetric distrubution of cellular components during these divisions helps establishing the ICM
2.Cell-cell signalling
a] What mechanisms establish and maintain the inner cell mass (ICM) in the blastocyst?
- Intercellular communication
- role:establish and maintain ICM
- Cells within ICM: cell signalling interaction for their self-renewal and pluripotent state
Important signalling pathway in ICM
* Fibroblast growth factor (FGF) signalling pathway
* >promote self-renewal of ICM
* Prevents their differentiation
3.Cell adhesion molecules
a] What mechanisms establish and maintain the inner cell mass (ICM) in the blastocyst?
- E-cadherin
- > integrity of ICM
- facilitate cell-cell adhesion and contribute to formation of cohesive ICM structure
Loss of cell adhesion would mean?
* Disrupt ICM
* Leads to differentiation of its cell
4.Transcriptional Regulation
a] What mechanisms establish and maintain the inner cell mass (ICM) in the blastocyst?
- Trancriptional factors
- Epigenetic modifications
- > establish and maintain pluripotent state of the ICM cells
Transcription factors
* Oct 4
* Nanog
* Sox2
* >maintain pluripotent state and repress genes promoting differentiation
Epigenetic modifications
* DNA methlation
* Histone modifications
* >regulate gene expression, maintain pluripotent state
List the 5 roles of the yolk sac development?
b] List the roles of the yolk sac in development
1.Nutrient storage and transfer
2. Blood cell formation
2. Early circulation and oxygenation
3. Extraembryonic membrane formation
4. Germ cell development
- Nutrient storage and transfer
b] List the roles of the yolk sac in development
- Yolk sac
- > provide nutrient to developing embryo
- stores yolk
- > nutrient rich substance absorbed by embryo cells gradually
- > proteins,lipids,vitamins
- > > necessary for early stages of embryonic growth and development
2.Blood cell formation
b] List the roles of the yolk sac in development
- yolk sac involved in production of blood cells during embryonic development
- > Initial site for hematopoiesis (production of blood cells)
- Primitive red blood cells
- some types of immune cells:macrophages produced within
3.Early circulation and oxygenation
b] List the roles of the yolk sac in development
Yolk sac
* responsible for initial circulation of the blood in developing embryo
* Blood vessels in yolk sac faciliate transport nutrients and oxygens->developing tissues
* this stage yolk sac: site for gas exchange(embryo aquire o2 and remove co2)
4.Extraembryonic membrane formation
b] List the roles of the yolk sac in development
- yolk sac
- acts one of the extraembryonic membranes:protect developing embryo
- Along with amnion, chorion. allantois, yolk sac contributes formation of membranes
- > protective environment, regulate fluid balance, aid in waste disposal during development
5.Germ cell development
b] List the roles of the yolk sac in development
Yolk sac
* involved in early development of primordial germ cells,
* >precursor of sperm and eggs
* Germs cells initially migrate from the yolk sac to developing gonads
* >where they undergo further development and differentiation
How do β-catenin-mediated signals contribute to the formationof the amphibian organizer; include a diagram to support your answer.
List the 4 ways
How do β-catenin-mediated signals contribute to the formationof the amphibian organizer; include a diagram to support your answer.
- Dorsal-ventral patterning
- Activation of target genes
- Regulation of Nodal signalling
- Axial mesoderm induction
1.Dorsal-Ventral Patterning
How do β-catenin-mediated signals contribute to the formation of the amphibian organizer; include a diagram to support your answer.
- B-catenin key component of Wnt signalling pathway
- > involved in dorsal-ventral patterning of embryo
- Absence of Wnt signalling, B-catenin target for degradation
- Wnt bind to receptors
- > stabilise and accumulates B-catenin in cytoplasm
- > acting as transcriptional co-activator.
2.Activation of target genes
How do **β-catenin-mediated signals contribute to the formation **of the amphibian organizer; include a diagram to support your answer.
- Nuclear B-catenin forms complex with transcription factors of theT-cell factor/lymphoid enhancer factor (TCF/LEF) family
- > compex binds specific DNA sequences ->promoter regions of target genes>activation
- > inducing TFs and signalling molecules(organiser formation and patterning)
Draw and fully label a diagram of the human embryo at the time implantation is initiated (E7.5).
Describe with a diagram how DNA methylation changes during pre-implantation embryo development, include the relevant enzymes that mediate the methylation changes
Maternal (pre-fertilisation) control molecules remain** present** through cleavage ** however
gene activation (embryonic gene expression) occurs early in the mammal
(unlike high yolk embryos) For embryonic gene activity the genome must be remodelled–
new histones are placed on the DNA
new DNA methylation patterns occur (generally unmethylated)
gamete pattern islost** and by 8/16 cells pluripotent pattern seen
