Lecture 20 Thursday November 22 2007
Reproductive cloning
- dolly
- cloning embryos
- worked well in cattle and has been done for years
- nucleous extraction
- replacement with chosen DNA
therapeutic cloning
- making stem cell lines
- this enables the regeneration of organs
fetal stem cells
- not as good as embryonic stem cells
- won't last forever
adult stem cells
- we don't have very many so finding them is difficult
existing human embryonic stem cell lines
- nov ery well characterized
- what we need is patient specific stem cell lines
patient specific stem cell lines
- these are good because they
ethical source o huan embryonic stem cells
- distribution of embryos
- source of eggs
derivation
- sperm + egg = embryo
- eight cell stage
- blastocist
standard nuclear transfer
altered nuclear transfer (how you get around not producing an embryo)
- somantic nuclei genetically modified to impair embryo 's ability to develop
- cdx2 is a transcription factor
- with out cdx2 you can no implant a stem cells
- can still isolate embryonic stem cell
- there are clear problems with this theory
parthenogenesis
- development of embryo from an egg without fetilization by sperm
- getting an embyo from an egg without fertilization
- this embryo will not develop - you need male genes
meiosis
- Two copies of a single chromosome
- line up to form bivalents
- meiosis one
- each cell has one chromosome that is duplicated
- first polar body is thrown away
- this is because of
- the egg is arrested after meiosis one
- stop it from going through second miotic division with drugs
- diploid cell will not develop but will give off stem cells
genomic imprinting
- in a few cases, gene expression depends which parent the allele came from
- paternal and maternal alleles are expressed differently
- controlled by modifications to the DNA that do not affect
imprinting process
- erase genes
- the result is that the males contribution in the parthogenesis - this alters gene expression in the embryo is deformed
organismically dead embryos
- needs OCT4 to divided beyond a certain stage
- however, at the point just before death stem cells are extracted
chromosomally abnormal embryos
- self normalization - genes fix themselves to create normal embryonic stem cells
single blastomere biopsy
- used today in medicine
- preimplantation genetic diagnnosis
- has the potential to damage the embryo
- remove a single cell from the embryo
- test it for disease
- wait for it divide by culturing it in vitro
- you can them make a stem cell line
somantic cell differentiation
- change a differentiated somantic cell into a pluripotent stem cell
dedifferentiation
- can you force a stem cell to de differentiate
- you stick them in a dish and reprogram it
- it loses its differentiated properties
epigenetics
- changing DNA without changing DNA sequence
- involves chromatin remodeling
- so you want to take permanently turned off genes and turn them back on
- you have to remove epigenetic marks
- it is the best way to go but is difficult
Human ESC lines
- 2004 published the creation of the first cloned human embryos
- he reported that he made 10
- no cloned human embryos
last week
- dr. shouklhat mitalipov at oregon health & science university
- cloned macque embryos
- using SCNT (skin cells)
- extracted stem cells from some of the cloned monkey embryos
- able to develop into mature heart and nerve cells in the laboratory
- took 10 years and 15000 eggs
Doll scientist abandons cloning - November 2007
- prof shinya Yamanaka of Kyotto Univeristy, Japan
- no eggs, or embryos
- generically modified human adult cells to make them almost as pluripotent as stem cells
- adding back genes allowed the genes to resume expression
- made 10 pluripotent lines from culture of 50, 000 skin
- used 4 transcription factor genes (MYC - is an oncagene that could turn into cancer) to add back
- adding extra copies of the gene
- Scientists are allowed to do this - no embryo's
adding back doesn't always work they have not refined
page revision: 1, last edited: 27 Nov 2007 15:25