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. 2023 Mar 10;14:1329. doi: 10.1038/s41467-023-37017-7

Fig. 4. Mef2D forms liquid-like and solid-like higher order assembly.

Fig. 4

a Mef2D foci in the nucleus and cytoplasm. Subcellular distribution of Mef2D wt, var3, var4 and var8 in C2C12 cells grown in cycling or differentiating medium exhibit foci formation in both the nucleus and cytoplasm. Higher-order assembly is most pronounced in case of var8 with rigid β-domain, but is also observed in case of var3 and var4 with mobile β-domain. 24 hrs post-transfection cells were fixed and stained with an antibody specific for Mef2D. Nucleic acid was stained using DAPI. The scale bar is 10 μm on the representative images. The experiment was performed four times (cycling medium) and three times (differentiating medium). Quantification is shown in panel b. b Quantification of MEF2D cells with cytoplasmic higher-order structures (foci). The percentage of Mef2D overexpressing cells with cytoplasmic aggregates is significantly higher in case of var8 with rigid β-domain. Cycling C2C12 cells: n = 4, ± s.e.m.; differentiating C2C12 cells: n = 3 independent experiments, ± s.e.m. Total number of cells counted > 150. Significances were computed by one-way ANOVA followed by Bonferroni-Holm Posthoc in reference to wt: var3 p = 0.13 (cycling) and p = 0.87 (differentiated), var4 p = 0.09 (cycling) and p = 0.60 (differentiated), var8 p = 0.04 (cycling) and p = 0.04 (differentiated). c, d Analysis of mobility of Mef2D higher-order assemblies in nuclear foci (c) and cytoplasmic foci (d). Mobility was assessed by fluorescence recovery after photobleaching (FRAP) performed after 24 hours post-transfection of GFP-tagged MEF2D wt, var3, var4 and var8 in C2C12 cells. The mean of the FRAP curve +/- standard error of the mean (s.e.m.) is shown. c Number of nuclear foci analyzed: wt (3); var3 (3); var4 (3); var8 (3). d number of cytoplasmic aggregates analyzed: wt (11); var3 (10); var4 (10); var8 (9). All Mef2D proteins show high mobility inside the nuclear foci (c) and nucleoplasm (Supplementary Fig. 5b). This is in sharp contrast with the low mobility inside cytoplasmic foci (d).