In PLoS Genetics this week, an international team of researchers report that nucleolin is required for DNA methylation and the expression of rRNA gene variants in Arabidopsis thaliana. In plants with a disrupted nucleolin-like protein gene, AtNUC-L1, transcription of rRNA variants is repressed, and the most highly represented rRNA gene variant, inactive in wild-type plants, is reactivated in AtNUC-L1 mutants, the researchers write. "We show that disruption of the AtNUC-L1 gene induces loss of symmetrical DNA methylation without affecting histone epigenetic marks at rRNA genes," the team adds, suggesting that this reveals a novel mechanism for rRNA gene transcriptional regulation and that "the nucleolin protein plays a major role in controlling active and repressed rRNA gene variants in Arabidopsis."
Researchers in the UK use a combination of growth analysis, molecular genetics and modeling to find the genetic factors that contribute to organ shape, which they report in PLoS Biology. Using a snapdragon flower as an example, the researchers show that growth is under the control of several dorsoventral genes which control flower shape. "The action of these genes can be modeled by assuming they modulate specified growth rates parallel or perpendicular to local orientations, established by a few key organizers of tissue polarity," the researchers write. This doesn't fully explain growth fields and shapes, but a model showing that dorsoventral genes also influence tissue polarity suggests that they play a key role in the development and evolution of shape.
In PLoS One this week, researchers at Harvard and Memorial Sloan-Kettering Cancer Center explore the therapeutic implications of plasticity of the cancer stem cell phenotype. In some tumor types, the presence of some extra- or intracellular signals induce cancer progenitors to revert back to a multipotential cancer stem cell state, the researchers write. They designed a mathematical model to investigate the dynamics of tumor progression in such cases, and found that "higher levels of dedifferentiation substantially reduce the effectiveness of therapy directed at cancer stem cells by leading to higher rates of resistance." Plasticity of the cancer stem cell phenotype is an important determinant of tumor prognosis, the researchers add.
And in PLoS Biology this week, researchers around the world collaborate to determine the evolutionary relationships of wild hominids as recapitulated by their gut microbial communities. By investigating the distal gut microbial communities harbored by great apes, the researchers found that "the branching order of the host-species phylogenies based on the composition of these microbial communities is completely congruent with the known relationships of the hosts." Although the gut is initially and continually seeded by bacteria from other sources, over the course of evolution, the composition of the great ape's gut microbiota is phylogenetically conserved.