Define cell potency:
- The ability for a cell to differentiate into different cell types
What are the 4 supportive membranes associated with amniotic vertebrate embryonic development?
- Amnion: encloses amniotic fluid which protects the embryo
- Chorion: gaseous exchange
- Allantois: holds nitrogenous wastes, contributes to gas exchange
- Yolk sac: nutrition source in egg laying amniotes
- in humans the yolk sac and allantois are incorporated into the umbilical chord
Describe the process by which a zygote becomes a blastocyst
- The zygote undergoes cleavage: a period of rapid cell division without growth in overall size of the embryo
- Once the embryo reaches the 8 cell stage it undergoes compaction- the cells become tightly joined
- The morula forms- inner and outer cells of embryo are defined
- The blastocyst forms- the inner cells move to one side of the embryo and a cavity forms
How are cells of the early blastocyst divided into trophoblast and hypoblast?
- This is determined by the contact the cell has with other cells on all sides (or lack thereof in trophooblast cells) causes the cells to express different factors
What factors to outer early blastocyst cells express?
- Cdx2 (which inhibits expression of Nanog and Oct4)
- they become trophoblast cells
What factors to inner early blastocyst cells express?
- Oct4, Nanog and Gata6= pluripotency factors
- they become inner cell mass cells
How does the inner cell mass divide into epiblast and hypoblast?
- Inner cell mass cells that express Nanog will become epiblast
- Inner cell mass cell that express Gata6 will become hypoblast
What is gastrulation?
- The formation of the 3 primary germ layers (ectoderm, mesoderm and endoderm) from the bilaminar disc
Explain the process of gastrulation:
- Epiblast cells migrate through the primative streak and displace the hypoblast forming the definitive endoderm
- More epiblast cells follow these migrating cells and form a middle layer creating the mesoderm
- the epiblast becomes ectoderm
What is the fate of the trophoblast?
- to form extraembryonic tissues such as the foetal part of the placenta
What is the fate of the epiblast?
- To form the embryo (3 germ layers) and amnion
What is the fate of the hypoblast?
- To form part of the yolk sac
What is regulative development?
- The ability of early mammalian embryos to produce a normal and complete organism even if cells are removed or added
e. g. an early embryo can split and both halves can form complete embryos- identical twins
What are some examples of ectoderm derived tissues?
- Epidermis
- Nerves
- Neural crest cells
What are some examples of mesoderm derived tissues?
- Bones and muscles
- Circulatory system
- Gonads
What are some examples of endoderm derived tissues?
- Epithelial lining of GI tract and associated organs
- Epithelial lining of respiratory ducts
- thymus
What is organogenesis?
- The differentiation and organisation of tissues from the 3 germ layers and their arrangement into organs
- Most organs are comprised of contributions from all 3 germ layers
What are the 2 key organisers in the early mammalian blastocyst?
- Specialised group of cells in the hypoblast- anterior ventral endoderm (AVE)
- Primative streak
How does the primative streak form?
- BMP4 of extraembryonic origin is secreted to the epiblast which instructs it to make Wnt and Nodal signalling molecules
- The AVE is at the anterior end and instructs the anterior epiblast to make Lefty and Cerberus signalling molecules that inhibits Wnt and Nodal production
- This means that the primative streak forms at the posterior end where Wnt and Nodal are expressed fully
What is neuralation?
The process of neural chord formation from ectoderm (neural plate) down the anterior-posterior axis - Neural chord induction is initiated by the underlying notochord sonic hedgehod signalling
