Figure 4.

SMN granules within neurites are deficient of Sm proteins in motor neurons. Primary cultured mouse motor neurons were double immunostained for SMN (A, in green) and Sm proteins (B, in red), a major component of snRNPs. Images were deconvolved, superimposed, and registered using fiduciary beads (arrows) in the mounting medium. A, SMN was prevalent in the nucleus and was distributed throughout the cytoplasm and neurites within granules. B, Sm proteins were highly enriched in the nucleus and showed significant staining only within the perinuclear cytoplasm, in which there was colocalization with SMN (C, merged colors, inset a enlarged in bottom row). C, In the neurite, a very low frequency of colocalized signal (in yellow) appeared. Sm protein levels in the middle neurite segment (see enlarged inset b in bottom row) were markedly reduced compared with SMN. In the distal neurite segment, the amount of Sm proteins was extremely low with respect to SMN (enlarged inset c).