Separation and subtyping of planarian neoblasts by density-gradient centrifugation and staining

A method has been devised to isolate neoblasts from planarians in high purity and high yield. Specimens of Dugesia polychroa and Dugesia tahitiensis were disintegrated mechanically. After several prepurification steps consisting in sequential filtering through increasingly fine meshes and differential centrifugation, the resulting cell suspension was separated by centrifugation in discontinuous density gradients formed from Percoll solutions. Isosmotic conditions were applied. Two gradients are recommended, one isopycnic four-step gradient (densities 1.03, 1.05, 1.07, 1.09) to obtain one single fraction with a high yield of neoblasts in high purity and one six-step gradient for preparing subfractions of neoblasts somewhat less pure, but in still greater amounts. This latter gradient (densities 1.04, 1.05, 1.06, 1.065, 1.07, 1.09) was run under conditions of rate zonal centrifugation and used for further subtyping of neoblasts by specific staining with azure A – eosin B. A first survey of tentative types based on morphological criteria is given. The viability of neoblasts isolated in the way described was tested in primary cell cultures. In current experiments, 6-week-old cultures had a viability of roughly 50%, with mitoses up to 1 week after the isolation of neoblasts. This revised version was published online in July 2006 with corrections to the Cover Date.