Editing Stem cell (section)

==Lineage==
{{Main|Stem cell line}}
Lineage is an important procedure to analyze developing embryos. Since cell lineages shows the relationship between cells at each division. This helps in analyzing stem cell lineages along the way which helps recognize stem cell effectiveness, lifespan, and other factors. With the technique of cell lineage mutant genes can be analyzed in stem cell clones that can help in genetic pathways. These pathways can regulate how the stem cell perform.<ref>{{cite journal |last1=Fox |first1=D.T. |last2=Morris |first2=L.X. |last3=Nystul |first3=T. |last4=Spradling |first4=A.C. |title=Lineage analysis of stem cells |journal=StemBook |year=2008 |doi=10.3824/stembook.1.33.1 |pmid=20614627 |url=https://www.stembook.org/node/542 |doi-access=free }}</ref>

To ensure self-renewal, stem cells undergo two types of cell division (see ''Stem cell division and differentiation'' diagram). Symmetric division gives rise to two identical daughter cells both endowed with stem cell properties. Asymmetric division, on the other hand, produces only one stem cell and a [[progenitor cell]] with limited self-renewal potential. Progenitors can go through several rounds of cell division before terminally [[cell differentiation|differentiating]] into a mature cell. It is possible that the molecular distinction between symmetric and asymmetric divisions lies in differential segregation of cell membrane proteins (such as [[receptor (biochemistry)|receptors]]) between the daughter cells.<ref>{{cite journal |last1=Beckmann |first1=Julia |last2=Scheitza |first2=Sebastian |last3=Wernet |first3=Peter |last4=Fischer |first4=Johannes C. |last5=Giebel |first5=Bernd |title=Asymmetric cell division within the human hematopoietic stem and progenitor cell compartment: identification of asymmetrically segregating proteins |journal=Blood |date=15 June 2007 |volume=109 |issue=12 |pages=5494–5501 |doi=10.1182/blood-2006-11-055921 |pmid=17332245 |doi-access=free }}</ref>

An alternative theory is that stem cells remain undifferentiated due to environmental cues in their particular [[Stem-cell niche|niche]]. Stem cells differentiate when they leave that niche or no longer receive those signals. Studies in ''Drosophila'' germarium have identified the signals [[decapentaplegic]] and adherens junctions that prevent germarium stem cells from differentiating.<ref>{{cite journal |last1=Xie |first1=Ting |last2=Spradling |first2=Allan C |title=decapentaplegic Is Essential for the Maintenance and Division of Germline Stem Cells in the Drosophila Ovary |journal=Cell |date=July 1998 |volume=94 |issue=2 |pages=251–260 |doi=10.1016/s0092-8674(00)81424-5 |pmid=9695953 |s2cid=11347213 |doi-access=free }}</ref><ref>{{cite journal |last1=Song |first1=X. |last2=Zhu |first2=CH |last3=Doan |first3=C |last4=Xie |first4=T |title=Germline Stem Cells Anchored by Adherens Junctions in the Drosophila Ovary Niches |journal=Science |date=7 June 2002 |volume=296 |issue=5574 |pages=1855–1857 |doi=10.1126/science.1069871 |pmid=12052957 |bibcode=2002Sci...296.1855S |s2cid=25830121 }}</ref>

In the United States, Executive Order 13505 established that federal money can be used for research in which approved human embryonic stem-cell (hESC) lines are used, but it cannot be used to derive new lines.<ref>{{cite web |date=9 March 2009 |title=Executive Order: Removing barriers to responsible scientific research involving human stem cells |url=https://obamawhitehouse.archives.gov/the_press_office/Removing-Barriers-to-Responsible-Scientific-Research-Involving-Human-Stem-Cells |work=[[whitehouse.gov]] |via=[[NARA|National Archives]]}}</ref> The National Institutes of Health (NIH) Guidelines on Human Stem Cell Research, effective July 7, 2009, implemented the Executive Order 13505 by establishing criteria which hESC lines must meet to be approved for funding.<ref>{{cite web |title=National Institutes of Health Guidelines on Human Stem Cell Research |url=http://stemcells.nih.gov/policy/pages/2009guidelines.aspx |access-date=24 April 2014}}</ref> The NIH Human Embryonic Stem Cell Registry can be accessed online and has updated information on cell lines eligible for NIH funding.<ref>{{cite web |title=NIH Human Embryonic Stem Cell Registry |url=https://grants.nih.gov/stem_cells/registry/current.htm |access-date=1 March 2017}}</ref>  There are 486 approved lines as of January 2022.<ref>{{cite web |title=NIH Human Embryonic Stem Cell Registry |url=https://grants.nih.gov/stem_cells/registry/current.htm#hold |access-date=10 February 2022}}</ref>