C. GFP immuno-EM staining in FGFR3/4KO chondrocytes infected with a constitutive nuclear (and active) mutant TFEB fused to GFP tag (TFEB- S142A:S211A-GFP). GFP positive gold immune-particles showed presence of GFP-puncta into the nucleus (N, stained in green for visualization). Lysosomes were stained in blue for visualization. Insets showed magnification of lysosomes. Quantification of lysosome diameter (nm) in control (wild type) and FGFR3;4KO chondrocytes infected with empty or with TFEB- S142A:S211A-GFP vector. Mean +/- standard error of the mean (sem) of N=3 biological replicates. n=40 (veh) n=78 (FGFR3;4KO) n=57 (FGFR3;4KO +TFEB-S142A:S211A-GFP) cells were analyzed. Scale bar 500 nm. Kruskal Wallis test p=1.43e-13; Nemenyi post hoc test ***p<0.0005; NS not significant. 