SUMMARY Background How morphogen gradients form has long been a subject of controversy. The strongest support for the view that morphogens do not simply spread by free diffusion has come from a variety of studies of the Decapentaplegic (Dpp) gradient of the Drosophila larval wing disc. Results In the present study, we initially show how the failure, in such studies, to consider the coupling of transport to receptor-mediated uptake and degradation has led to estimates of transport rates that are orders of magnitude too low, lending unwarranted support to a variety of hypothetical mechanisms, such as “planar transcytosis” and “restricted extracellular diffusion”. Using several independent dynamic methods, we obtain data that are inconsistent with such models, and that show directly that Dpp transport occurs by simple, rapid diffusion in the extracellular space. We discuss the implications of these findings for other morphogen systems in which complex transport mechanisms have been proposed. Conclusions We believe that these findings resolve a major, longstanding question about morphogen gradient formation, and provide a solid framework for interpreting experimental observations of morphogen gradient dynamics.

Cholesterol crystals (ChCs) have been identified as a major factor of plaque vulnerability and as a potential biomarker for atherosclerosis. Yet, due to the technical challenge of selectively detecting cholesterol in its native tissue environment, the physiochemical role of ChCs in atherosclerotic progression remains largely unknown. In this work, we demonstrate the utility of hyperspectral stimulated Raman scattering (SRS) microscopy combined with second-harmonic generation (SHG) microscopy to selectively detect ChC. We show that despite the polarization sensitivity of the ChC Raman spectrum, cholesterol monohydrate crystals can be reliably discriminated from aliphatic lipids, from structural proteins of the tissue matrix and from other condensed structures, including cholesteryl esters. We also show that ChCs exhibit a nonvanishing SHG signal, corroborating the noncentrosymmetry of the crystal lattice composed of chiral cholesterol molecules. However, combined hyperspectral SRS and SHG imaging reveals that not all SHG-active structures with solidlike morphologies can be assigned to ChCs. This study exemplifies the merit of combining SRS and SHG microscopy for an enhanced label-free chemical analysis of crystallized structures in diseased tissue.

No abstract

Spaceflight affects numerous organ systems in the body, leading to metabolic dysfunction that may have long-term consequences. Microgravity-induced alterations in liver metabolism, particularly with respect to lipids, remain largely unexplored. Here we utilize a novel systems biology approach, combining metabolomics and transcriptomics with advanced Raman microscopy, to investigate altered hepatic lipid metabolism in mice following short duration spaceflight. Mice flown aboard Space Transportation System -135, the last Shuttle mission, lose weight but redistribute lipids, particularly to the liver. Intriguingly, spaceflight mice lose retinol from lipid droplets. Both mRNA and metabolite changes suggest the retinol loss is linked to activation of PPARα-mediated pathways and potentially to hepatic stellate cell activation, both of which may be coincident with increased bile acids and early signs of liver injury. Although the 13-day flight duration is too short for frank fibrosis to develop, the retinol loss plus changes in markers of extracellular matrix remodeling raise the concern that longer duration exposure to the space environment may result in progressive liver damage, increasing the risk for nonalcoholic fatty liver disease.