FOCAL POINT  (Left to right) Michael Bloodgood, Hai Le, Antony Jose, and colleagues investigate how C. elegans maintains tissue homogeneity by examining why, in the absence of the exonuclease ERI-1 (right), only some intestinal cells silence the expression of nuclear-localized GFP from a repetitive transgenic array. The researchers find that, in the absence of ERI-1, dsRNA produced from the transgene can stably silence GFP expression via the canonical RNAi pathway. This dsRNA is unequally segregated during the division of the blastomere that gives rise to intestinal cells, leading to the variation in transgene expression. ERI-1 maintains homogenous expression across the tissue by lowering dsRNA levels below a threshold required to initiate silencing.

PHOTO COURTESY OF THE AUTHORS