RNAi in Xenopus: look before you leap.

RNAi has revolutionized reverse genetics; however, RNAi is not necessarily ubiquitous or constitutive. Lund and colleagues (pp. 1121-1131) show that microRNA (miRNA) effector Argonautes (Agos) are limiting and easily saturated during early Xenopus embryogenesis. Moreover, this stage is devoid of slicing capacity. Supplementation of Ago proteins rescued endogenous miRNA activity in the presence of exogenous siRNAs, and, excitingly, ectopic Ago2 could now support RNAi in Xenopus. These observations may potentially facilitate RNAi in other recalcitrant model organisms.