Editing Human cloning (section)

==Methods==

===Somatic cell nuclear transfer (SCNT)===
{{Main|Somatic cell nuclear transfer}}
[[File:Cloning diagram english.svg|thumb|upright=1.3|Diagram of SCNT process]]

In somatic cell nuclear transfer ("SCNT"), the nucleus of a [[somatic cell]] is taken from a donor and transplanted into a host [[Oocyte|egg cell]], which had its own genetic material removed previously, making it an enucleated egg. After the donor somatic cell genetic material is transferred into the host oocyte with a micropipette, the somatic cell genetic material is fused with the egg using an electric current. Once the two cells have fused, the new cell can be permitted to grow in a [[In vivo|surrogate]] or [[In vitro|artificially]].<ref>{{cite book |last= Gilbert |first= Scott F. |date=30 June 2013 |title= Developmental Biology| edition= 10th |publisher=Sinauer Associates, Inc. |pages=32–33 |isbn=9780878939787 }}</ref> This is the process that was used to successfully clone Dolly the sheep (see {{section link|#History}}).<ref name="TIME"/> The technique, now refined, has indicated that it was possible to replicate cells and reestablish pluripotency, or "the potential of an embryonic cell to grow into any one of the numerous different types of mature body cells that make up a complete organism".<ref>{{Cite web|url=https://www.britannica.com/science/cloning|title=cloning {{!}} Definition, Process, & Types|website=Encyclopædia Britannica|language=en|access-date=16 December 2019|archive-date=26 April 2020|archive-url=https://web.archive.org/web/20200426233507/https://www.britannica.com/science/cloning|url-status=live}}</ref>

===Induced pluripotent stem cells (iPSCs)===
{{Main|Induced pluripotent stem cell}}
[[File:Overview of iPS cells.png|thumb|upright=1.25|Overview of iPS cells]]

Creating induced [[Pluripotency|pluripotent]] [[stem cell]]s ("iPSCs") is a long and inefficient process. [[cell potency|Pluripotency]] refers to a stem cell that has the potential to [[cellular differentiation|differentiate]] into any of the three [[germ layers]]: [[endoderm]] (interior stomach lining, gastrointestinal tract, the lungs), [[mesoderm]] (muscle, bone, blood, urogenital), or [[ectoderm]] (epidermal tissues and nervous tissue).<ref name=Binder>{{cite book|editor-last1= Binder| editor-first1= Marc D.|title=Encyclopedia of Neuroscience|year=2009|publisher=Springer|location=Berlin|isbn=978-3540237358|edition=online|editor-last2=Hirokawa| editor-first2= Nobutaka| editor-first3= Uwe |editor-last3= Windhorst}}</ref> A specific set of genes, often called "reprogramming factors", are introduced into a specific adult cell type. These factors send [[cell signalling|signals]] in the mature cell that cause the cell to become a pluripotent stem cell. This process is highly studied and new techniques are being discovered frequently on how to improve this induction process.

Depending on the method used, reprogramming of adult cells into iPSCs for [[Implantation (human embryo)|implantation]] could have severe limitations in humans. If a virus is used as a reprogramming factor for the cell, cancer-causing genes called [[oncogenes]] may be [[regulation of gene expression|activated]]. These cells would appear as rapidly dividing cancer cells that do not respond to the body's natural cell signaling process. However, in 2008 scientists discovered a technique that could remove the presence of these oncogenes after pluripotency induction, thereby increasing the potential use of iPSC in humans.<ref name="Cancer threat removed">{{cite news |url=http://www.latimes.com/news/nationworld/nation/la-sci-stemcell6-2009mar06,0,63456.story |title=Cancer threat removed from stem cells, scientists say |newspaper=Los Angeles Times |first=Karen |last=Kaplan |date=6 March 2009 |access-date=15 April 2014 |archive-date=10 March 2009 |archive-url=https://web.archive.org/web/20090310085937/http://www.latimes.com/news/nationworld/nation/la-sci-stemcell6-2009mar06,0,63456.story |url-status=live }}</ref>

===Comparing SCNT to reprogramming===
Both the processes of SCNT and iPSCs have benefits and deficiencies. Historically, reprogramming methods were better studied than SCNT derived embryonic stem cells (ESCs).<ref name=TrounsonComment/> However, more recent studies have put more emphasis on developing new procedures for SCNT-ESCs. The major advantage of SCNT over iPSCs at this time is the speed with which cells can be produced. iPSCs derivation takes several months while SCNT would take a much shorter time, which could be important for medical applications. New studies are working to improve the process of iPSC in terms of both speed and efficiency with the discovery of new reprogramming factors in oocytes.{{citation needed|date=May 2014}} Another advantage SCNT could have over iPSCs is its potential to treat [[mitochondrial disease]], as it uses a donor oocyte.<ref name=TrounsonComment/> No other advantages are known at this time in using stem cells derived from one method over stem cells derived from the other.<ref name="pmid24180743">{{cite journal |vauthors= Langerova A, Fulka H, Fulka J | title = Somatic cell nuclear transfer-derived embryonic stem cell lines in humans: pros and cons | journal = Cellular Reprogramming | volume = 15 | issue = 6 | pages = 481–3 |date= 2013 | pmid = 24180743 | doi = 10.1089/cell.2013.0054 }}</ref>

{{clear}}