Interaction between MED12 and ΔNp63 activates basal identity in pancreatic ductal adenocarcinoma.

The presence of basal lineage characteristics signifies hyperaggressive human adenocarcinomas of the breast, bladder and pancreas. However, the biochemical mechanisms that maintain this aberrant cell state are poorly understood. Here we performed marker-based genetic screens in search of factors needed to maintain basal identity in pancreatic ductal adenocarcinoma (PDAC). This approach revealed MED12 as a powerful regulator of the basal cell state in this disease. Using biochemical reconstitution and epigenomics, we show that MED12 carries out this function by bridging the transcription factor ΔNp63, a known master regulator of the basal lineage, with the Mediator complex to activate lineage-specific enhancer elements. Consistent with this finding, the growth of basal-like PDAC is hypersensitive to MED12 loss when compared to PDAC cells lacking basal characteristics. Taken together, our genetic screens have revealed a biochemical interaction that sustains basal identity in human cancer, which could serve as a target for tumor lineage-directed therapeutics.

An RNA exosome subunit mediates cell-to-cell trafficking of a homeobox mRNA via plasmodesmata.

Messenger RNAs (mRNAs) function as mobile signals for cell-to-cell communication in multicellular organisms. The KNOTTED1 (KN1) homeodomain family transcription factors act non­cell autonomously to control stem cell maintenance in plants through cell-to-cell movement of their proteins and mRNAs through plasmodesmata; however, the mechanism of mRNA movement is largely unknown. We show that cell-to-cell movement of a KN1 mRNA requires ribosomal RNA­processing protein 44A (AtRRP44A), a subunit of the RNA exosome that processes or degrades diverse RNAs in eukaryotes. AtRRP44A can interact with plasmodesmata and mediates the cell-to-cell trafficking of KN1 mRNA, and genetic analysis indicates that AtRRP44A is required for the developmental functions of SHOOT MERISTEMLESS, an Arabidopsis KN1 homolog. Our findings suggest that AtRRP44A promotes mRNA trafficking through plasmodesmata to control stem cell­dependent processes in plants.

Assessment of the Bone Mineral Content in the Mandible by Dual-Energy X-Ray Absorptiometry to Evaluate Short-Term Change.

With the objective of being able to assess response to disease or clinical treatment, the densitometry community has long sought the ability to assess short-term change in bone density. The mandible, known to have a high bone turnover, an increased vascularity, and a greater susceptibility to osteoclastic and osteoblastic activities, has long been suggested but has fallen short as a site from which to monitor an early change in the response to a treatment or a disease. The current study developed a method to assess bone density in the superimposed left and right mandibles. Examining a skull in a positioning platform showed that studies between -5.0° and +12.5° from the preferred 0° orientation generated studies that were statistically similar to studies in the preferred orientation. After establishing the distribution of bone density in the mandibles, a software was developed that would execute a search for an area of intermediate content within the body and ramus regions of the mandible; in subsequent studies of the same individual, the analysis software would place the body and ramus regions in the same location without operator dependence. Studies in a population of subjects showed that the density in the body and ramus regions varied independently and that the density in these regions was independent of age. Repeat studies with repositioning showed repeatability of 1.73% and 2.44% for the body and ramus, resulting in computed least significant change limits of 4.84% for the body and 6.83% for the ramus. Examining 45 subjects undergoing treatment for osteoporosis up to over 46 wk showed 22 (49%) subjects with an increase in 1 of the mandible sites, suggesting a benefit from treatment, whereas 12 (27%) subjects showed a decrease in both mandible sites, suggesting a poor response to treatment. We conclude that applying the methodology and allowing the software to locate and define regions of interest allow assessments of change in the bone mineral content at the mandible that will reflect early changes occurring with disease or treatment.