GED L20 Flashcards
Describe the experiment which led to the conclusion of totipotency of cells & name the scientist responsible
• Separation of 1st 2 blastomeres -> Sea urchin eggs: (Hans Diresch)
- Each cell at the 2-cell stage or 4-cell stage of meiosis are totipotent.
»_space; Cell has capacity to generate totality of cells present in an organism.
Describe what baby hair ligature experiments revealed & how this was done & name the scientist involved.
• Baby hair ligature experiments: (Hans Spemann)
First nuclear transplantation experiments.
Using baby hair to separate 1st 2 cells of frog embryo.
» Both cells develop into entire embryos rather than half an embryo.
If Incomplete separation of cells using hair;
Continuous nuclear division -> one cell
»_space; Develops sufficiently small nucleus to enter other cell via hole
»_space; Other cell (previously not containing nucleus) -> develop into whole
Embryo.
> Illustrate 16 cell stage nuclei are totipotent
(Whole embryo can develop from stage 16 cell.)
Describe the experiment illustrating the natural loss of cell totipotency over time & nam ethe scientist involved
Cloning of frog embryos: (Briggs & King)
Nuclei up to blastula stage could produce entire embryo -> Totipotent.
Nuclei further developed than blastula stage -> Not Totipotent.
»_space; More differentiated cells lose their ability of totipotency over time.
What is the Waddington Landscape Hypothesis?
Waddington Landscape Hypothesis:
Totipotent cells become differentiated
> Once differentiation begins, it cannot be reversed.
> Potency decreases over time.
Describe the first successful cloning experiment of an entire organism & name the scientist involved
Cloning Protocol: (John Gurdon)
Extraction -> Terminally different pigmented cells -> Tadpole epithelia.
> Transplanted into denucleated wild type (pigmented) eggs
-> (Denucleated via UV radiation)
Serial transplantations -> Produced blastula stage embryos
»_space; Died.
Transplant nuclei -> Dying blastula stage embryo -> Into Albino type Eggs
> Repeat several times.
Eventually developed fully formed identical frogs
Define Pluripotency
• Pluripotency:
- Cellular ability / potential -> Differentiate into any type of cell except embryonic / placental cells.
- Cellular ability / potential -> Differentiate into any type of cell from a distinct set of cells.
Define Bipotency
• Bipotency:
- Cellular ability / potential -> Differentiate into any of two particular types of cell.
• Unipotency:
- Cellular ability / potential -> Differentiate into one particular type of cell only.
Define Totipotency
• Totipotency
- Cellular ability / potential -> Differentiate into any type of cell
- Ability / potential of a blastomere -> produce a fully-developed embryo.
Define Unipotency
• Unipotency:
- Cellular ability / potential -> Differentiate into one particular type of cell only.
Describe the first experiment to successfully clone a mammalian blastocyst & name the scientists involved
• Cloning of Mammals -> Dolly the Sheep: (Campbell & Wilmut)
Nuclear Transfer -> Cultured cell line
- Donors:
Eggs -> Scottish Blackface.
» Denucleated
Udder cells -> Finn-Dorset
- Transfer udder cells -> denucleated egg.
- Fused with electric current & cultured
» Development -> Blastocyst
- Transferred to Scottish blackface surrogate
» Birth of Finn-Dorset lamb
> Genetically identical -> Nuclear donor (Udder cells)
Describe the trophectoderm of early mammalian blastocysts
- Trophectoderm:
» Outer layer of cells of a blastocyst.
» Provide nutrients -> the developing embryo, facilitate attachment to the uterine
lining and become part the placenta.
Describe the blastocoel of early mammalian blastocysts
- Blastocoel:
» Fluid-filled, inner cavity of a blastocyst resulting from cleavage of the oocyte after
fertilization.
Describe the epiblast of early mammalian blastocysts
- Epiblast: (Primitive mesoderm)
» Forms embryo proper
» Cell layer -> develops from inner cell mass (accumulation of cells attached to inner
lining of trophoblast) of blastocyst.
» Differentiates -> Ectoderm, mesoderm & endoderm
» Develops -> Extraembryonic membranes.
Describe the hypoblast / primitive endoderm of early mammalian blastocysts
- Hypoblast (Primitive endoderm)
» Forms inner cell mass
» Layer of cells which enclose epiblast / accumulation of cells attached -> trophoblast & separate from blastocoel.
» Develops -> Extraembryonic membranes
Describe the development of development of stem cells using nuclear programming
Treatment of Early Blastocysts / epiblasts -> certain conditions
» Produce permanently pluripotent cells
> Leads -> concept of embryonic stem cells.
Permanently pluripotent blastocysts
»_space; Genetically modified -> Generation of specific cell pathway / lineage
> Grow in culture
> Remove factors ensuring blastocysts remain pluripotent
Describe the basis of knowledge used to enable development of stem cells by nuclear programming
- Extra-embryonic membrane -> Unique to mammals
» Provides nutrients -> Embryo - Early stage blastocysts totipotent
» Dev. -> Extra-embryonic mem & entire organism - Blastocysts -> Not totipotent
» Dev. -> Everything but extra-embryonic mem.
What is the source of pre-implantation embryos / embryonic stem cells?
- Epiblast of pre-implantation embryos / Embryonic Stem Cells
Source of pluripotent stem cells
»_space; Ability to produce all somatic & germ cells -> Except extraembryonic membranes.
»_space; Permanent maintenance -> Pluripotent abilities in culture.
Describe the potency of an epiblast of an early mammalian embryonic stem cell
> > Ability to produce all somatic & germ cells -> Except extraembryonic membranes.
»_space; Permanent maintenance -> Pluripotent abilities in culture.
Describe the uses of stem cells
Uses:
Study of in-vitro development
Transplant -> Blastocysts
»_space; Dev. of genetically modified organisms.
Generation -> Teratomas.
»_space; Benign Tumors
> Differentiate outside normal env.
–> Generate new tissues
-> (No metastasis but can use to predict potential dev. of embryonic stem cells)
Study of disease & organ pathologies
Used -> Drug screening
Development of knockout genes
Growth of organs/tissues
Eg. Eyeball, Parts of Brain, Neurons, Cortex Tissue, Spinal Chords.
- Led to significant replacement of animals in research.
Who was responsible for the development of regenerative medicine methods & what did they do?
(Yoshiki Sasai)
Growth of organs/tissues
Eg. Eyeball, Parts of Brain, Neurons, Cortex Tissue, Spinal Chords.
Briefly describe the method of reprogramming differentiated cells & name the scientist responsible
• Reprogramming Differentiated cells: (Shinya Yamanaka)
Differentiated cells reprogrammed -> return to Pluripotent Embryonic state
» Without use of nuclear transplantation.
»_space; Production -> Induced Pluripotent Stem (iPS) cells
Describe the process of differential cell reprogramming
Process:
- Various solutions of gene mixtures added -> Fibroblasts
» Investigate which mixtures reprogramme cells
> Produce Pluripotent Embryonic cells
What were the results of differential cell reprogramming?
Result:
- Generation of clones -> Induced Pluripotent Stem (iPS) stem cells
» Act like Embryonic stem cells -> iPS
> Cocktail : Klf-4, Sox-2, Oct4, Myc
What are cell reprogramming / iPS cells used for? List some of their benefits.
Uses / Benefits:
- Can use any cell Eg. Skin -> Produce Pluripotent stem cells
» Embryonic stem cells not required -> Ethics
- Produce pluripotent stem cells
» Determine / manipulate development -> specific required cells.
- Produce genetically modified organism
- Used to generate human iPS cells
- Taken from those with disease
» Model diseases in vitro for investigation rather than patient
- Use in transplants
» Production of cells / organs / tissues which are not immunologically rejected.
- Produce iPS cells from patients
» Cell replacement therapies / regenerative medicine.
