Stem cells are defined in functional terms as having both the ability to replenish themselves through cell division and the ability to differentiate into specialized cell types. Stem cells are found in all multicellular organisms, including two broadly-defined cell types: embryonic stem cells (ESCs) that are derived from the inner cell mass of blastocyst-stage embryos and adult stem cells that are present in adult tissues. Stem cells can now be grown and transformed in vitro into specialized cells with characteristics that are consistent with those of cell types found in various tissues, such as muscles or nerves. Highly plastic adult stem cells isolated from a variety of sources, including umbilical cord blood and bone marrow, are routinely used in medical therapies.

Nuclear reprogramming refers to the erasure and remodeling of epigenetic marks, such as DNA methylation, which is a part of normal mammalian development. After fertilization, the paternal and maternal genomes (excepting differentially methylated regions associated with imprinted genes) are demethylated and remethylated. This reprogramming is likely required for totipotency of the newly formed embryo and erasure of acquired epigenetic changes. In vitro manipulation of preimplantation embryos has been shown to disrupt methylation patterns at imprinted loci, and such disruption plays a crucial role in the development of cloned animals.

Advances in stem cells and nuclear reprogramming shall provide new insights into the mechanisms of cellular differentiation, during embryonic development as well as in adult tissues, and insights which may lead to therapies for several human diseases. The special issue will emphasize novel approaches for understanding mechanisms that underlie the phenomenon of stem cells derivation, reprogramming, and development. Potential topics include, but are not limited to:

• Derivation of embryonic stem cells (ESCs)
• Derivation of induced pluripotent stem (iPS) cells
• Potentials of ESC and iPS for cell-based therapies
• Somatic cell nuclear transfer (NT), stem cells derived from NT, and related reprogramming events
• Epigenetics of stem cells
• Adult stem cells, pluripotency, and applications

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