Study published in Stem Cell also shows that miRNAs made specifically by ESCs almost all share the same seed sequence, which could be the key to properties like self renewal.

An international research team report that embryonic stem cells share the same profile of miRNAs. They examined 14 different strains of human embryonic stem cells and compared them to a large group of other cell types.

“We report the most comprehensive determination of microRNA expression in human embryonic stem cells to date,” according to study leader Jeanne Loring, Ph.D., a professor at Scripps Research and director of the Scripps Research Center for Regenerative Medicine. “Our most important discovery is that microRNAs made specifically by human embryonic stem cells almost all share the same seed sequence. Seed sequences are the parts of miRNAs that interact with cellular machinery and regulate synthesis of proteins.

“We’re certain that the shared seed sequences aren’t an accident. Embryonic stem cells are actively and robustly preventing the synthesis of certain proteins, and this may be key to maintaining their unique qualities of self-renewal and pluripotence.”

The researchers also found that a proportion of miRNAs in human embryonic stem cells occur in clusters in the genome, including two very large clusters not previously associated with stem cells. Because of its location in the genome, one of the clusters could play a role in chromosomal abnormalities that often lead to the development of cancer, they suggest.

Furthermore, the investigators showed that oncogenic miRNAs, which are associated with human cancers, are overrepresented in human embryonic stem cells, while tumor suppressor miRNAs are rare. This implies that while human embryonic stem cells are not closely related to any one type of cancer cell, they may share some self-renewal mechanisms with cancer cells as a class, the authors wrote.

Investigators involved in the study came from The Scripps Research Institute, Illumina, Tel Aviv University, and Universitätsklinikum Schleswig-Holstein. The study was published on April 10 in an advance, online edition of Stem Cells.

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