Lecture 31 Flashcards
What does an embryo begin as? what does this give rise to? What are the exceptions?
The embryo begins as a small number of naive totipotent cells, these embryonic stem cells can give rise to all cell types except trophectoderm, which make up the outside of the blastocyst (making them pluripotent). These cells will progressively restrict their cell fate until terminally differentiated, at which point they’ll only be able to give rise to the same type of cell. The exception to this are the stem cells and germ cells (eggs and sperm).
What are these terms: trophectoderm, Inner cell mass, blastocyst, totipotent, pluripotent
The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast.
Totipotent cells can form all the cell types in a body, plus the extraembryonic, or placental, cells. Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent. Pluripotent cells can give rise to all of the cell types that make up the body.
How does embryonic cell differentiation work? Give an example
The cells fate becomes determined due to factors such as environment and the necessary control gene becomes activated, this causes the cell to produce a particular protein which causes it to become a blast cell for a cell type e.g MyoD gene is activated leading to production of MyoD protein which causes the cell to become a myoblast.
Next the cell becomes differentiated. The protein increases transcription of itself and of proteins necessary for that cell type and stops the cell cycle e.g MyoD increases transcription of more MyoD and of muscle proteins and stops the cell cycle, eventually leading to a multinucleate muscle cell.
Why are stem cells different?
They can divide without limit and are mostly undifferentiated. They are capable of giving rise to both stem cells and cells which will go on to differentiate into functional tissue cells.
What is the difference between adult and embryonic stem cells? How do we persuade stem cells to become what we want?
Embryonic stem cells are pluripotent (fertilised eggs are totipotent), this essentially gives them the ability to produce all cell types. Adult stem cells such as bone marrow cells usually only give rise to one or a few cell types.
Different culture conditions can be used to persuade stem cells to develop into different kinds of differentiated cells (so long as the stem cell can).
Why are adult stem cells important and what are some main types? What is plasticity? How does the production of the differentiated cells work?
Adult stem cells are important for tissues such as blood and skin which need constant renewing, blood stem cells (haematopoietic stem cells) are found in bone marrow and can be used for transplants. The bone marrow also contains mesenchymal stem cells which can give rise to bone and cartilage cells, they may also be able to renew other tissues (known as plasticity).
The process works like this: the stem cell divides to produce one stem cell and one intermediate cell, this intermediate cell will then divide a variable amount of time before becoming the differentiated cells (these differentiated cells could all be different types).
Why is umbilical cord freezing common practice?
The stem cells are immature blood stem cells which can be used to treat leukaemias and other blood diseases.
What are induced pluripotent stem cells and how are they made?
These are pluripotent stem cells produced by reprogramming of adult skin cells.
What is gene therapy and how does it work? What is a possible method for this?
Gene therapy is a proposed way of correcting single gene disorders through insertion of a normal allele into the cells (best applied to the stem cells as these corrected stem cells will keep dividing and passing on the correct gene) of the affected tissue.
One possible way to do this is to use retroviruses containing the corrected allele (RNA version) to infect cultured bone marrow cells from the patient and then re insert these infected cells into the patient.
What is somatic cell nuclear transfer? How does it work? What cells are best for this?
A method of cloning done by destroying the nucleus of an egg cell and adding in a new nucleus. The egg is then activated to begin development. The best nucleuses for this are embryonic, already differentiated nucleuses are not the same and do not have a high chance of success relatively.
Why are some cells better for somatic cell nuclear transfer than others?
During differentiation most animal cells generally lose the ability to regenerate the whole organism because the nuclear DNA cannot reset itself to an embryonic state.
How was dolly the sheep cloned and what DNA did it have?
mammary cells of one sheep were cultured and fused with egg cells (without a nucleus) from another sheep. This was then grown in culture and implanted in a third sheep. Only a tiny amount resulted in a live birth (1 in 276). Dolly the sheep had the nuclear genome from the mammary cell donor, mitochondrial genome from the egg donor and no DNA from the surrogate mother.
What has trichostatin been used for?
Trichostatin has been used in somatic cell nuclear transfer to remove many issue associated with age of the individual which was cloned from.
Why would cloning humans not necessarily produce the expected results?
Cloning doesn’t reproduce an individuals personality and cannot bring people back.
What is therapeutic cloning, how is it done and what can it be used for?
Therapeutic cloning involves the creation of personalized embryonic stem cells, this is done through a donor nucleus in an egg with a removed nucleus (enucleated) and then cultured until the blastocyst stage, the embryonic stem cells can then be made from this blastocyst and cultured under various conditions to make special cell types to order. This can also be done with induced pluripotent cells of people with genetic disorders to make cells or tissues for drug testing.
