A New Directionality Software Tool Reveals Muscle Microtubule Pattern Alterations

Cytoskeletal components have distinct patterns, whose modifications may indicate pathological changes. However, the changes may be difficult to assess visually. For example, recent data show that microtubules play a role in Duchenne Muscular Dystrophy pathology. We and others have reported, earlier, that the microtubules of the mdx (dystrophin-null) mouse are perturbed. Although it was possible to assess microtubule patterns in fibers of adult fast muscles (EDL) visually, it was not possible to do so in fibers from slow muscles (Soleus), which have a more tangled microtubule pattern. We need a robust tool to analyze the digital images, more specifically to detect the directionality of the microtubule network. The most commonly used tool is based on the Tamura method, which is calculated from 3 x 3 edge filters. This approach mainly focuses on local image features while neglecting the global features. We find that this method is not well suited to the structure of microtubules. We have therefore developed a new directionality detection method utilizing texture features. The software generates a graphic by calculating the texture correlation for each orientation. Both local and global features contribute to the final results. A direct visual comparison of the produced images makes it easy for the user to distinguish subtle variations in pattern. A directionality score is also calculated based on the peak sharpness in the plot. This new tool was used to compare microtubules in the soleus muscle of wild-type, mdx, utrophin-null and double knockout mice. The directionality scores revealed differences among these mouse lines which could not be appreciated visually and which paralleled the differences observed in EDL muscles.