In a study out of Michigan that seems to have overturned the cancer stem cell theory, researchers found that after introducing human melanoma cells into immunocompromised mice, many more than expected developed tumors. In the less immunocompromised mice, only one in 837,000 cells regenerated melanoma, while in the more vulnerable mice one in four cells did, says a related news story. "We're not trying to claim there is no merit to the field, but we think that the frequency of cancer stem cells will be much higher," says Sean Morrison, a co-author, in this Wired story.
Another study from Michigan scientists shows that changes in a stem cell's orientation with respect to the niche during aging add to the decline in spermatogenesis in Drosophila. "These observations provide a much clearer picture of the aging Drosophila testis, and hint at processes that may limit cell production in many other tissues: stem-cell homeostatic mechanisms are not perfect, and cannot maintain full activity even into middle age," says a related news story.
Australian and Italian scientists have used a combination of molecular and genetic assays to show that in mice, Sox18 acts as a molecular switch to induce differentiation of lymphatic endothelial cells. Sox18 is expressed in certain cardinal vein cells and overexpressing the gene in blood vascular endothelial cells triggered Prox1 expression, while embryos lacking Sox18 didn't show lymphatic endothelial cell differentiation from the cardinal vein.
Harvard scientists have found a protein network that stabilizes rDNA repeats in S. cerevisiae via interactions between rDNA-associated silencing proteins and two proteins of the inner nuclear membrane. Deleting either the INM or silencing proteins reduces perinuclear rDNA positioning, disrupts the nucleolus–nucleoplasm boundary, induces the formation of recombination foci, and destabilizes the repeats, they write in the abstract.