Totipotent

Cell potency is a cell's ability to differentiate into other cell types.The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum, begins with totipotency to designate a cell with the most differentiation potential, pluripotency, multipotency, oligopotency, and finally unipotency. Cell potency is a cell's ability to differentiate into other cell types.The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum, begins with totipotency to designate a cell with the most differentiation potential, pluripotency, multipotency, oligopotency, and finally unipotency. Totipotency (Lat. totipotentia, 'ability for all ') is the ability of a single cell to divide and produce all of the differentiated cells in an organism. Spores and zygotes are examples of totipotent cells.In the spectrum of cell potency, totipotency represents the cell with the greatest differentiation potential, being able to differentiate into any embryonic cell, as well as extraembryonic cells. In contrast, pluripotent cells can only differentiate into embryonic cells. It is possible for a fully differentiated cell to return to a state of totipotency. This conversion to totipotency is complex, not fully understood and the subject of recent research. Research in 2011 has shown that cells may differentiate not into a fully totipotent cell, but instead into a 'complex cellular variation' of totipotency. Stem cells resembling totipotent blastomeres from 2-cell stage embryos can arise spontaneously in mouse embryonic stem cell cultures and also can be induced to arise more frequently in vitro through down-regulation of the chromatin assembly activity of CAF-1. The human development model is one which can be used to describe how totipotent cells arise. Human development begins when a sperm fertilizes an egg and the resulting fertilized egg creates a single totipotent cell, a zygote. In the first hours after fertilization, this zygote divides into identical totipotent cells, which can later develop into any of the three germ layers of a human (endoderm, mesoderm, or ectoderm), or into cells of the placenta (cytotrophoblast or syncytiotrophoblast). After reaching a 16-cell stage, the totipotent cells of the morula differentiate into cells that will eventually become either the blastocyst's Inner cell mass or the outer trophoblasts. Approximately four days after fertilization and after several cycles of cell division, these totipotent cells begin to specialize. The inner cell mass, the source of embryonic stem cells, becomes pluripotent. Research on Caenorhabditis elegans suggests that multiple mechanisms including RNA regulation may play a role in maintaining totipotency at different stages of development in some species. Work with zebrafish and mammals suggest a further interplay between miRNA and RNA-binding proteins (RBPs) in determining development differences. In mouse primordial germ cells, genome-wide reprogramming leading to totipotency involves erasure of epigenetic imprints. Reprogramming is facilitated by active DNA demethylation involving the DNA base excision repair enzymatic pathway. This pathway entails erasure of CpG methylation (5mC) in primordial germ cells via the initial conversion of 5mC to 5-hydroxymethylcytosine (5hmC), a reaction driven by high levels of the ten-eleven dioxygenase enzymes TET-1 and TET-2. In cell biology, pluripotency (Lat. pluripotentia, 'ability for many ') refers to a stem cell that has the potential to 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 system). However, cell pluripotency is a continuum, ranging from the completely pluripotent cell that can form every cell of the embryo proper, e.g., embryonic stem cells and iPSCs (see below), to the incompletely or partially pluripotent cell that can form cells of all three germ layers but that may not exhibit all the characteristics of completely pluripotent cells. Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a 'forced' expression of certain genes and transcription factors. These transcription factors play a key role in determining the state of these cells and also highlights the fact that these somatic cells do preserve the same genetic information as early embryonic cells. The ability to induce cells into a pluripotent state was initially pioneered in 2006 using mouse fibroblasts and four transcription factors, Oct4, Sox2, Klf4 and c-Myc; this technique, called reprogramming, earned Shinya Yamanaka and John Gurdon the Nobel Prize in Physiology or Medicine 2012. This was then followed in 2007 by the successful induction of human iPSCs derived from human dermal fibroblasts using methods similar to those used for the induction of mouse cells. These induced cells exhibit similar traits to those of embryonic stem cells (ESCs) but do not require the use of embryos. Some of the similarities between ESCs and iPSCs include pluripotency, morphology, self-renewal ability, a trait that implies that they can divide and replicate indefinitely, and gene expression. Epigenetic factors are also thought to be involved in the actual reprogramming of somatic cells in order to induce pluripotency. It has been theorized that certain epigenetic factors might actually work to clear the original somatic epigenetic marks in order to acquire the new epigenetic marks that are part of achieving a pluripotent state. Chromatin is also reorganized in iPSCs and becomes like that found in ESCs in that it is less condensed and therefore more accessible. Euchromatin modifications are also common which is also consistent with the state of euchromatin found in ESCs.