The surprisingly simple recipe for starting to grow a limb

How do organisms form limbs in the womb? Scientists have been striving to answer this question not only to deepen our understanding of evolution and embryonic development, but also to help make the dream of regenerating partial ...

How jellyfish regenerate functional tentacles in days

At about the size of a pinkie nail, the jellyfish species Cladonema can regenerate an amputated tentacle in two to three days—but how? Regenerating functional tissue across species, including salamanders and insects, relies ...

Dissecting the structural secrets of the inactive X chromosome

Cell biologists from RIKEN have provided an unprecedented glimpse into the distinctive features of an unusual chromosome—the inactivated X chromosome copy carried by every female cell. The findings are published in the ...

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Embryonic stem cell

Embryonic stem cells (ES cells) are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells.

Embryonic Stem (ES) cells are pluripotent. This means they are able to differentiate into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. These include each of the more than 220 cell types in the adult body. Pluripotency distinguishes ES cells from multipotent progenitor cells found in the adult; these only form a limited number of cell types. When given no stimuli for differentiation, (i.e. when grown in vitro), ES cells maintain pluripotency through multiple cell divisions. The presence of pluripotent adult stem cells remains a subject of scientific debate; however, research has demonstrated that pluripotent stem cells can be directly generated from adult fibroblast cultures.

Because of their plasticity and potentially unlimited capacity for self-renewal, ES cell therapies have been proposed for regenerative medicine and tissue replacement after injury or disease. However Diseases treated by these non-embryonic stem cells include a number of blood and immune-system related genetic diseases, cancers, and disorders; juvenile diabetes; Parkinson's; blindness and spinal cord injuries. Besides the ethical concerns of stem cell therapy (see stem cell controversy), there is a technical problem of graft-versus-host disease associated with allogeneic stem cell transplantation. However, these problems associated with histocompatibility may be solved using autologous donor adult stem cells or via therapeutic cloning.

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