Fig. 4a-e.

Gems represent a distinct category of nuclear bodies by ultrastructural analysis. a,b Double immunoelectron labeling illustrating the distribution of coilin (large gold particles) and SMN (survival of motor neurons protein product; small gold particles) in nuclear bodies from differentiated UR61 cells upon 36 h of dexamethasone treatment. a A typical Cajal body (CB) composed of coiled dense threads appears decorated with large and small gold particles. b This nuclear body of granular nature and moderate electron density, identified as a gem, is only labeled with small gold particles, whereas some nucleoplasmic large particles (arrows) are seen in the vicinity of this body. c To confirm the ultrastructure of gems, we used the cellular model of MEF42, which does not contain coilin, but accumulates gems. Simple immunogold labeling for SMN reveals an immunolabeled nuclear body (gem) identical to that described in b corresponding to a UR61 cell. d Double immunolabeling of a CB-gem pair in a differentiated UR61 cell. Large particles decorate the dense threads of the CB, whereas small particles appear segregated on the associated granular body. e This CB, double immunolabeled for coilin and SMN, has an associated mass of amorphous low density material free of both molecular constituents. Bar represents 100 nm