Science and Reason: MicroRNA and stem cells

I've written about both microRNA and stem cells recently. But there is more news that reports on connections between the two.

Following are summaries of the announcements.

Role Of Tiny RNAs In Controlling Stem Cell Fate Identified (3/6/08): The microRNAs miR-1 and miR-133 have been known to be associated with muscle development. The new research shows that they actively encourage heart muscle development and suppress genes that could cause pluripotent embryonic stem cells to turn into undesired cells like neurons or bone. The two miRNAs turn on genes that encourage mesoderm formation. They also turn off genes that cause stem cells to become ectodermal or endodermal cells.

Research abstract: MicroRNA Regulation of Cell Lineages in Mouse and Human Embryonic Stem Cells.
Blog post: here.
Short RNA Strand Helps Exposed Skin Cells Protect Body From Bacteria, Dehydration And Even Cancer (3/2/08): In a wide range of vertebrates, from zebrafish to chickens and humans, miR-203 is found only in very specific types of skin – the outer layers of stratified epithelial tissues. In the 13th day of mouse embryo development, the embryo's skin is primarily composed of undifferentiated stem cells, and there is very little miR-203 in the cells. During the next two days expression of miR-203 rises rapidly, and the cells begin to differentiate into cells that form the outermost, protective layer of skin.

When miR-203 was artificially caused to be expressed too early, the normal rapid proliferation of stem cells was significantly slowed. The effect was attributed to inhibition of the p63 gene, which normally encourages stem cell proliferation, by miR-203. On the other hand, when miR-203 was suppressed, cells in the outer layer proliferated significantly more than normally, because p63 was not being inhibited.

p63 is a master regulatory gene, which maintains pluripotency in skin stem cells. It is often found to be overexpressed in cancerous cells. Future research will explore whether low expression of miR-203 is associated with cancer, and if so, whether increasing miR-203 expression is helpful.

More: here.
MicroRNA Pathway Essential For Controlling Self-renewal Of Stem Cells (2/15/07): The gene Dicer-1 (Dcr-1) has been known to affect expression of specific miRNAs in fruit flies (Drosophila). It is essential for generating mature miRNAs from their corresponding precursors. This research shows that unmutated Dcr-1 is necessary for controlling self-renewal or maintenance of germline stem cells and somatic stem cells in Drosophila ovaries. The researchers infer that lack of miRNAs, due to mutant Dcr-1, is responsible for failure of self-renewal of stem cells, but specific miRNAs that are affected are yet to be determined.

Research abstract: Dcr-1 Maintains Drosophila Ovarian Stem Cells.
Blog post: here.