Natural fiber exoskeletons of insects and arthropods. In shells and exoskeletons, the chitin fibers contribute to their hierarchical structure. In nature, pure chitin (100% acetylation) does not exist. It instead exists as a copolymer with chitin's deacetylated derivative, chitosan. When the acetylized composition of the copolymer is over 50% acetylated it is chitin. This copolymer of chitin and chitosan is a random or block copolymer. Chitosan is a deacetylated derivative of chitin. When the acetylized composition of the copolymer is below 50% it is chitosan. Chitosan is a semicrystalline “polymer of β-(1-4)-2-amino-2-deoxy-D-glucose”. One difference between chitin and chitosan is that chitosan is
Epiblast-derived stem cell EpiLC was shown to cause a reversion back to an ESC-like state (with levels of Alkaline Phosphatase staining recovered to that observed in ESCs as well as more ESC-like cell morphology), with Klf2 being required for the mechanism to occur. It has been proposed that PRDM14 induces this state by activating Klf2 via active demethylation recruitment of Oct-4; such technique has yet to be demonstrated in actual epiblast-derived EpiSCs. Epiblast-derived stem cell After the blastocyst stage, once an embryo implanted in endometrium (in case of rodent), the inner cell mass (ICM) of a fertilized embryo segregates into two layers: hypoblast