“…Moreover, mature miRNAs exert their repressive function in association with a member of the Argonaute (Ago) protein family (reviewed by Iwakawa and Tomari, 2015), and the removal of this Ago effector protein has also been a useful tool for assessing the contribution of miRNA-mediated repression to different processes. For instance, in Caenorhabditis elegans, zygotic removal of both miRNA-dedicated Argonautes, ALG-1 and ALG-2, causes embryonic arrest during morphogenesis (Vasquez-Rifo et al, 2012). In mice, two Ago2 null alleles lead to developmental arrest around embryonic day (E) 5.5 or 7.5 (Alisch et al, 2007;Morita et al, 2007), and loss of Dicer1 also causes early embryonic lethality, with animals arresting before E7.5, prior to the body plan being established (Bernstein et al, 2003); however, it should be noted that Dicer is also involved in the endo siRNA pathway, so a contribution from this other class of small RNAs should be considered in the interpretation of such experiments.…”