Fig. 1

Expression and distribution of mRNP granule proteins in isolated skeletal muscle fibers. A Schematic of an isolated myofiber (MF) depicting myonuclei (MN) and an associated muscle satellite cell (MuSC). The longitudinal striations represent orientation of the myofibrils while the cross-striations represent the A-band (A) and Z line (Z). B–D, B’–D’ Depict magnified views of the regions enclosed by brackets (dotted lines) in B–D to visualize subcellular distribution of Fmrp. Arrow heads indicate cytoplasm, double arrows indicate nucleus. Fmrp puncta are observed both in nucleus and cytoplasm of MuSC (B, B’) and as cross-striated staining in myofiber. Puncta also accumulate in a cytoplasmic domain adjacent to the MN, while MN is itself not stained (C, C’). Nuclear accumulation of Fmrp is also seen in the Pax7⁺ MuSC nucleus (D, D’) but not in an adjacent Pax7^- MN. B’, C’, and D’ represent single-channel (488) images. E–G Distribution of Fmrp puncta (green) in myofiber in a cross-striated pattern congruent with Z lines revealed by α-actinin (red). Arrows in G point to Fmrp puncta co-localizing with α-actinin striations. H–I. Secondary antibody controls (mouse and rabbit) do not show either punctate or striated background. K Distinct GW182 bodies are visible in Pax7⁺ MuSC. Pax7^- MN also show distinct perinuclear puncta (arrowheads) and significant punctate staining is observed in MF cytoplasm in a doublet striated pattern likely reflecting A-band localization. K’ Region within brackets in k magnified to show GW182 puncta in the MuSC nucleus (double arrow). L, L’ No enrichment (either nuclear or cytoplasmic) is detected of Dcp1a in MuSC nucleus (marked with the membrane marker Caveolin 1). Faint fibrillar puncta are observed in myofibers. M, M’ Xrn1 is faintly detected in MuSC, but strongly expressed in myofibres in both a longitudinal and cross-striated pattern. K’, L’, and M’ represent single channel (green) images of enlarged areas indicated by brackets in K, L, and M, respectively