welcome again today we've come tolook at the applications of stem cells in the treatment of degenerative diseasespecifically taking a look at how stem cells have been applied to treatstargardt's disease stem cells are cells that the power to produce more ofthemselves and to differentiate and to become other cell types. differentiationinvolves the expression of some genes but not others the capacity of stem cells to divide and todifferentiate along different pathways is necessary in embryonic development and thisis what makes stem cells suitable for therapeutic uses when life begins a sperm cell fertilizes and egg cell to produce a zygote. this
zygote in the human body has thepotential to go on to form all of the extra embryonic membranes that set thestage for development the placenta the amnion the chorion and also to then allowthe fetus to develop all the complex tissues of the body including twohundred and twenty cells. this very first cell from which life begins is allpowerful it is totipotent because it possesses the capacity to form anorganism including all the cell types of the body. this fertilized egg or zygote then goeson to divide by mitosis two form a ball of a few cells called the morula at the twocell stage the four cell stage and even
up to the 8 cell stage these cellscan be separated and each one possesses the capacity to go on to developindependently into a new human being in other words allof these cells are totipotent but once the embryo begins to developfurther to form the blastocyst which consists of an outer layer or trophoblast..has now taken on the role of forming theextra embryonic membranes and the cells within this hollow ball or the innercell mass they are the ones that was possess the capacity to form all of theother cell types of the body minus the extra embryonic membranes thesecells are known as pluripotent because they can form all of this cell types ofthe body but they cannot on their own give rise to a
new organism. when we speak of embryonicstem cells it is really these cells of the inner cell mass of the blastocyst that but we speak of for they have thecapacity to develop and to differentiate into all of this cell types of the humanbody and if an embryonic stem cell is removed and put into the right cultureit would propagate itself and remain in the embryonic stem cell stage so howthen can embryonic stem cells be used in the treatment of stargardt's diseasestartgardt's disease is an eye disorder otherwise known as a retinopathy, where the cellsof the retina are unable to carry out their functions effectively and visionprogressively deterioates. stargardt's typically shows up in the teen yearsin most patients. it's brought about mainly
by the presence of a recessive alleleabca4 gene which is responsible for the production of a transmembrane proteinthat regulates active transport in some of the tissues of the eye. if this proteinis not functioning properly then a substance known as lipofuscin accumlates in the retinal pigment epithelium andthis leads to progressive degeneration of the retinal epithelial cells and thenthe cones which give vision and vison gradually begins to deteriorate. so how then canembryonic stem cells be used to treat stargardt's disease? well once the cellsof the inner cell mass have been put into a culture then biologists canfigure out what factors need to be
introduced into this culture to allowthe undifferentiated embryonic stem cells to begin to differentiate retinalpigment epithelium and once this formula was discovered then it was possible toproduce retinal pigment epithelium sheets to introduce them into stargardt'spatients. this was achieved for the first time in 2010 and it was a great breakthrough for the application of embryonic stem cells in the treatment ofdegenerative diseases but the use of these embryonic stem cells does not comewithout some issues first of all the tissue generated from the embryonic stemcells is not a genetic match with the patients receiving the transplant sothere could be the issue of
immunogenicity. the very use of an embryo isa highly controversial topic. for where does this embryo come from and toexamine this we need to go have a look at ivf in vitro fertilization ivf is a procedure that's been around foralmost 40 years being carried out for the first time in 1978. the purpose of in vitrofertilization is to allow the sperm and the egg to come together in lab conditions to allowfertilization to happen and then to replace the fertilized egg into thefemale reproductive system to allow development. it was developed to allowinfertile couples to have the opportunity to bear children of their own. but because of the (in)efficiency of in vitro fertilization andthe fact that it is very difficult to
get fertilization to happen in the firstplace and secondly to get implantation ivf clinics need to produce multiplefertilized eggs for each patient and what this does is it creates left over embryos possible humanlife forms which are left in petri dishes in the lab, frozen or disposed of.when research began into human embryonic stem cells this provided a great source of embryonic stem cells.yet the use remained controversial for the status of this early embryoremained questionable and the question was asked: wheteher or not one life was being taken tobring relief of suffering to another. another topic that's related to this therapeuticuse of embryonic stem cells is somatic celll nuclear transfer. carried out for the firsttime in frogs in 1958 and then
replicated in sheep in the nineteennineties today we understand that the nucleus of a somatic cell can possiblyreplace the nucleus of a fertilized egg allowing for a clone of this donor cellto develop so in the case of the treatment of stargardt's disease toavoid immune rejection it could be possible for the very patient to donatea skin cell lets say into an enucleated oocyte. allowing that encucleated oocyte to generate an embryo and thenharvest those stem cells to produce retinal pigmented sheet but in theparticular case of stargardt's disease which is usually genetic treatment in this way with therapeuticcloning would not be the right way to go
for the very genes which reside in this somatic cell will thenexpress themselves again and allow for the symptoms of stargardt's disease toreturn in time but perhaps it might be possible to relieve the immune rejectionissues by allowing for a sibling donor to provide a somatic cell remove its nucleus. place into a fertilized egg.stimulate it to develop. allow an embryo to develop. then harvest the embryonic stem cells treat itwith growth factors and allow for the development of the retinal pigmentedsheet which is then placed into the eye of the sibling recipient in this casebecause of the close genetic match you would have a cure for stargardt'sdisease and also a relief of the problem of immunogenicity. this somatic cell nucleartransfer leads to the production of a
clone of the human donor and if thiswere allowed to go on to develop in vivo(in a woman's uterus). it would give rise to a clone ofthe donor. of course human cloning is currently seen as highly unethical andis unlikely to happen in the near future but the production of embryos which arepotential human beings will allow for therapeutic cloning and where diseases donot have a genetic basis. the very patient can donate cells which in turn would generate embryos toproduce the cultures that would then generate the cells required. but is therea way to escape the whole issue of having to produce an embryo a potentiallife-form and to then take that life form apart. is there a way to get away from theembryonic stem? this was the question
that was asked by two japaneseresearchers and by 2007 shinya yamanaka and his team created induced pluripotent stem cells but the induced pluripotent stem cellis the subject another lesson
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