Reprogramming

In biology, reprogramming refers to erasure and remodeling of <a href="/facts/Epigenetics/UfAAERcn">epigenetic</a> marks, such as <a href="/facts/DNA_methylation/npoRhsnX">DNA methylation</a>, during mammalian development or in cell culture. Such control is also often associated with alternative covalent modifications of <a href="/facts/Histones/krb5VJfp">histones</a>.
Reprogrammings that are both large scale (10% to 100% of epigenetic marks) and rapid (hours to a few days) occur at three life stages of mammals. Almost 100% of epigenetic marks are reprogrammed in two short periods early in development after <a href="/facts/Fertilization/g8u3UKzF">fertilization</a> of an <a href="/facts/Egg_cell/gJyW3W3W">ovum</a> by a <a href="/facts/Sperm/RCxpXygQ">sperm</a>. In addition, almost 10% of <a href="/facts/DNA_methylation/npoRhsnX">DNA methylations</a> in <a href="/facts/Neuron/G7CyTVdH">neurons</a> of the hippocampus can be rapidly altered during formation of a strong fear memory. 
After fertilization in mammals, <a href="/facts/DNA_methylation/npoRhsnX">DNA methylation</a> patterns are largely erased and then re-established during early embryonic development. Almost all of the methylations from the parents are erased, first during early <a href="/facts/Embryogenesis/1lFY4EoW">embryogenesis</a>, and again in <a href="/facts/Gametogenesis/vgd0vV0R">gametogenesis</a>, with demethylation and remethylation occurring each time. Demethylation during early embryogenesis occurs in the preimplantation period. After a sperm fertilizes an <a href="/facts/Egg_cell/gJyW3W3W">ovum</a> to form a <a href="/facts/Zygote/mSu2xMWA">zygote</a>, rapid <a href="/facts/DNA_demethylation/3UxQyVGy">DNA demethylation</a> of the paternal DNA and slower demethylation of the maternal DNA occurs until formation of a <a href="/facts/Morula/PXJ8T2Ve">morula</a>, which has almost no methylation. After the <a href="/facts/Blastocyst/WkRkxdzc">blastocyst</a> is formed, methylation can begin, and with formation of the <a href="/facts/Epiblast/H6RSfpQy">epiblast</a> a wave of methylation then takes place until the <a href="/facts/Implantation_(embryology)/k6XJfNMv">implantation</a> stage of the embryo. Another period of rapid and almost complete demethylation occurs during gametogenesis within the primordial <a href="/facts/Germ_cell/1kY5KaR1">germ cells</a> (PGCs). Other than the PGCs, in the post-implantation stage, methylation patterns in somatic cells are stage- and <a href="/facts/Tissue_(biology)/H7CpML7A">tissue</a>-specific with changes that presumably define each individual <a href="/facts/Cell_type/1boyDWXb">cell type</a> and last stably over a long time.

Reprogramming open-in-new

Reprogramming