Ractopamine Rapid Test (Tissue)

Tendons and ligaments are crucial components of the musculoskeletal system, yet the pathways specifying these fates remain poorly defined. Through a screen of known bioactive chemicals in zebrafish, we identified a new pathway regulating tendon cell induction. We established that statin, through inhibition of the mevalonate pathway, causes an expansion of the tendon progenitor population. Co-expression and live imaging studies indicate that the expansion does not involve an increase in cell proliferation, but rather results from re-specification of cells from the neural crest-derived sox9a(+)/sox10(+) skeletal lineage. The effect on tendon cell expansion is specific to the geranylgeranylation branch of the mevalonate pathway and is mediated by inhibition of Rac activity. This work establishes a novel role for the mevalonate pathway and Rac activity in regulating specification of the tendon lineage.

As surfaces for enzyme immobilization, lipid bilayers (LBs) have the potential to exhibit chaperone-like activity, which can greatly enhance enzyme stability. Here, it is shown that this stabilizing effect can be generalized to a broad range of enzymes by modifying the mixed lipid composition based on the properties of the enzyme. This is demonstrated by analyzing the stability of nitroreductase, lipase, organophosphorus hydrolase, and lysozyme on LBs composed by mixing zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine with anionic 1,2-dioleoyl-sn-glycero-3-phospho-(1 '-rac-glycerol) or cationic 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine. Interestingly, while the optimal lipid composition exhibits a zeta potential with the same sign as each enzyme, the stabilizing compositional ranges are broad, and mixed lipid LBs are more stabilizing than homogeneous LBs with similar charge. This suggests that net charge and compositional heterogeneity are both important factors. Moreover, the degree of stabilization on appropriate bilayers under extremely denaturing conditions (7murea) is unprecedented, and activity of the enzymes is up to three-fold greater than that of the soluble enzyme at each enzyme's temperature optimum. By correlating enzyme diffusion on LBs with information about re-folding kinetics derived from single-molecule measurements, the influence of charge and composition on enzyme-LB interactions is shown, providing a rationale for the stabilizing effect of heterogeneous LBs.