Alphabet soup is not tasty, but must be devoured by any researcher. Some of the acronyms in biology, though, stand out for their importance and FRAP is one of them. FRAP is a very handy technique for studying the dynamics of proteins in a cell, and the paper from today’s image is a great example of how elegant and informative FRAP can be.
Titin is an abundant muscle protein that provides structural support for the sarcomere, which is the basic contracting unit in muscle. There are many isoforms of titin that allow structural and mechanical changes of the muscle tissue throughout development and during disease. The sturdiness that titin provides muscles may give an impression of a lack of dynamics, but a recent paper shows exactly the opposite. The authors in this study use a technique called fluorescence recovery after photobleaching (FRAP). In this case, fluorescently labeled titin was photobleached using a high power laser. By watching if and how the photobleached region recovers new fluorescent titin over time, da Silva Lopes and colleagues concluded that titin is very mobile and dynamic. Titin maintains unrestricted movement around sarcomeres, and this movement is dependent on calcium. In the images above, two different sized regions (top, bottom) of fluorescently-tagged titin within sarcomeres were photobleached. In both cases, the bleached regions (arrowheads in middle images) quickly recovered the titin fluorescent label (right) to levels similar to pre-bleach images (left).
da Silva Lopes, K., Pietas, A., Radke, M., & Gotthardt, M. (2011). Titin visualization in real time reveals an unexpected level of mobility within and between sarcomeres originally published in The Journal of Cell Biology, 193 (4), 785-798 DOI: 10.1083/jcb.201010099