Kremen is required for neural crest induction in Xenopus and promotes LRP6-mediated Wnt signaling

Kremen 1 and 2 (Krm1/2) are transmembrane receptors for Wnt antagonists of the Dickkopf (Dkk) family and function by inhibiting the Wnt co-receptors LRP5/6. Here we show that Krm2 functions independently from Dkks during neural crest (NC) induction in Xenopus. Krm2 is co-expressed with, and regulated by, canonical Wnts. Krm2 is differentially expressed in the NC, and morpholino-mediated Krm2 knockdown inhibits NC induction, which is mimicked by LRP6 depletion. Conversely, krm2 overexpression induces ectopic NC. Kremens bind to LRP6, promote its cell-surface localization and stimulate LRP6 signaling. Furthermore, Krm2 knockdown specifically reduces LRP6 protein levels in NC explants. The results indicate that in the absence of Dkks, Kremens activate Wnt/beta-catenin signaling through LRP6.     

Synthesis and biological evaluation of a new series of N-ylides as protein farnesyltransferase inhibitors

A new family of 30 benzoylated N-ylides 4 and 5 was synthesized and evaluated for the inhibitory activity on human protein farnesyltransferase. Most of these novel compounds possessed in vitro inhibition potencies in the micromolar range. The nature of the substituents on the pyridine and phenyl units proved to be important in determining inhibitory activity and generally, the replacement of the cyanoacrylonitrile function by a cyanoethylacrylate group decreased the biological potential on farnesyltransferase. These results completed our SAR study on this original class of N-ylides.     

Non-analytical methods for the estimation of total yolk carotenoids in passerine eggs

Carotenoids are essential antioxidant micronutrients. Oviparous species acquire carotenoids from their food and deposit them in the egg yolk, where they support embryonic development. The total carotenoid concentration in the egg yolk is typically measured analytically, which requires time, equipment and expertise, and can limit the sample available for other measurements, at least in species laying small eggs. Here we evaluate whether yolk colour can be used as a reliable alternative measure for total yolk carotenoid concentration. We compare two non-analytical methods, digital photography and visual colour scoring, using eggs from a wild population of Blue Tits Cyanistes caeruleus. Yolk hue estimated from digital photographs correlated more strongly with total yolk carotenoid concentration measured by high-performance liquid chromatography (HPLC) than did the visually assessed colour score based on a Yolk Colour Fan. Previous results based on HPLC measurements of total carotenoid concentration could be reproduced using yolk hue measurements. The results suggest that measuring yolk hue is a suitable proxy for assessing natural variation in total yolk carotenoid concentration in eggs of free-living birds.     

Reproducibility of two-dimensional gel electrophoresis at different replication levels

Reliability of two-dimensional electrophoresis differential display experiments depends on the reproducibility of the separations. The contribution of biological and technical variation to the overall variance of the two-dimensional patterns was estimated based on the factors found to influence spot volume variance. The second dimension and the staining were responsible for most of the spot volume variance, while using pooled samples lowered biological variation to the level of technical variation.     

The MRH protein Erlectin is a member of the endoplasmic reticulum synexpression group and functions in N-glycan recognition

Kremen1 and 2 (Krm1/2) are coreceptors for Dickkopf1 (Dkk1), an antagonist of Wnt/beta-catenin signaling, and play a role in head induction during early Xenopus development. In a proteomic approach we identified Erlectin, a novel protein that interacts with Krm2. Erlectin (XTP3-B) is member of a protein family containing mannose 6-phosphate receptor homology (MRH-, or PRKCSH-) domains implicated in N-glycan binding. Like other members of the MRH family, Erlectin is a luminal resident protein of the endoplasmic reticulum. It contains two MRH domains, of which one is essential for Krm2 binding, and this interaction is abolished by Krm2 deglycosylation. The overexpression of Erlectin inhibits transport of Krm2 to the cell surface. Analysis of its embryonic expression pattern in Xenopus reveals that Erlectin is member of the endoplasmic reticulum synexpression group. Erlectin morpholino antisense injection leads to head and axial defects during organogenesis stages in Xenopus embryos. The results indicate that Erlectin functions in N-glycan recognition in the endoplasmic reticulum, suggesting that it may regulate glycoprotein traffic.