Conventional myosin II activity provides the motile force for axon outgrowth, but to achieve directional movement during axon pathway formation, myosin activity should be regulated by the attractive and repulsive guidance cues that guide an axon to its target. Here, evidence for this regulation is obtained by using a constitutively active Myosin Light Chain Kinase (ctMLCK) to selectively elevate myosin II activity in Drosophila CNS neurons. Expression of ctMLCK pan-neurally or in primarily pCC/MP2 neurons causes these axons to cross the midline incorrectly. This occurs without altering cell fates and is sensitive to mutations in the regulatory light chains. These results confirm the importance of regulating myosin II activity during axon pathway formation. Mutations in the midline repulsive ligand Slit, or its receptor Roundabout, enhance the number of ctMLCK-induced crossovers, but ctMLCK expression also partially rescues commissure formation in commissureless mutants, where repulsive signals remain high. Overexpression of Frazzled, the receptor for midline attractive Netrins, enhances ctMLCK-dependent crossovers, but crossovers are suppressed when Frazzled activity is reduced by using loss-of-function mutations. These results confirm that proper pathway formation requires careful regulation of MLCK and/or myosin II activity and suggest that regulation occurs in direct response to attractive and repulsive cues.

No abstract

An ion paired reversed -phase high performance liquid chromatographic assay for iothalamic acid and para aminohippuric acid in the same sample of plasma is described. The analysis uses one internal standard for both drugs. Sample preparation consists of precipitating plasma proteins with methanol and centrifuging to settle the proteins. The supernatant is evaporated and the residue reconstituted with mobile phase for injection. For HPLC a Cg column and a mobile phase consisting of potassium phosphate buffer with dodecyl triethyl ammonium phosphate IP reagent, 22.5 % methanol and 2.5 % acetonitrile with UV detection at 254 nm was used.Coefficients of variation for the assay were in the range of 1.6 -12.1%for iothalamic acid and 4.3 -17.7% for para aminohippuric acid for four levels of concentration. Limits of quantitation were 3.0 pg/mL for iothalamic acid and 5.0 pglmL for para aminohippuric acid. This isocratic HPLC assay is simple, rapid and relatively inexpensive. 2395

No abstract

No abstract