Sarcomeric actin undergoes turnover in adult muscles.

<p>(A) Graphic representation of the experimental design for the pulse-chase experiments. Act88F::GFP or eGFP was expressed under the control of the TARGET system for 28 hours directly after eclosion (the pulse) and then shut off (the chase). (B, B′) Localization of eGFP (B) or Act88F::GFP (B′) when expressed throughout development and adulthood with the Mef2:GAL4 system (F-actin is counterstained with rhodamine-phalloidin). eGFP non-specifically labels the whole sarcomere while Act88F::GFP is specifically localized to the sarcomeric core. (C,D) A time series of representative images of IFMs from flies expressing eGFP (C) or Act88F::GFP (D) under the control of the TARGET system (F-actin counterstained with rhodamine-phalloidin). The locations of the Z-discs and M-lines are indicated by a ‘z’ or ‘m’ in both panels. (E) Quantification of fluorescent intensity at the Z-disc for eGFP during TARGET pulse-chase experiment. Intensity at the Z-disc increased during the 28 hr pulse phase but did not decline afterwards. Instead, intensity remained elevated. (F) Quantification of fluorescent intensity at the Z-disc for Act88F::GFP during TARGET pulse-chase experiment. Intensity at the Z-disc increased during the 28 hour pulse phase and then gradually declined. (G) The ratio of Z-disc to sarcomere body fluorescent intensity during the pulse-chase experiment shows that the increase in staining intensity is specific to the Z-disc for Act88F::GFP. Comparison of Z-disc to sarcomere body intensity ratios for eGFP (grey bars) and Act88F::GFP (black bars) expression shows that while eGFP localization is non-specific, Act88F::GFP is significantly enriched at the Z-disc. (H) Examples showing how Z-disc and sarcomere intensity was measured for both TARGET>eGFP and TARGET>Act88F::GFP myofibrils. Phalloidin counterstains were used to identify relevant areas. Red rectangles indicate the area quantified for Z-disc intensities. Irregular blue tetragons indicate the area quantified for sarcomere body intensities. For (E,F,G) N≥40 individual sarcomeres from ≥5 animals. For all panels, error bars indicate standard error; ns indicates not significant; * indicates a p-value<0.05, ** indicates a p-value<0.005, *** indicates a p-value<0.0005. TARGET>eGFP and TARGET>Act88F::GFP are abbreviated as T>eGFP and T>Act88F::GFP throughout.