UC Irvine

Quantitative evaluation of cellular morphology is crucial to understanding development and pathology of striated muscle tissues, including skeletal and cardiac myocytes. Striated myocytes are composed of parallel myofibrils, which are spanned by repeating sarcomere units that produce a contractile force parallel to the thick myosin filaments as they slide past the thin actin filaments. As sarcomeres produce the force necessary for contraction, assessment of sarcomere order is paramount in characterization of cardiac and skeletal myocytes. The uniaxial force produced by sarcomeres is ideally perpendicular to their z-lines, which couple parallel myofibrils and give cardiac and skeletal myocytes their distinct striated appearance. Accordingly, sarcomere structure is often evaluated by staining for z-line proteins such as α-actinin and titin, as well as actin. Despite their importance, challenges such as isolating z-lines from regions of off-target staining that occur along immature stress fibers and cell boundaries, a lack of metrics that summarize important and relevant aspects of sarcomeric architecture, and quantitatively studying striated myocytes in the presence of other cell types, have gone largely unaddressed. While an expert can qualitatively appraise tissues, these challenges leave researchers without robust, repeatable tools to assess striated myocyte morphology and behavior across different labs and experiments. Furthermore, the criteria used by experts to evaluate sarcomeric architecture have not been well-defined. We address these challenges by developing image processing pipelines to isolate structures of interest and providing metrics that summarize distinct aspects of cellular architecture in multiple different striated muscle tissues, imaged with various modalities. Characterization of striated myocyte morphology using the metrics discussed and implemented in this work can quantitatively evaluate striated muscle tissues and contribute to a robust understanding of the development and mechanics of striated muscles.