Piwi proteins, together with their associated Piwi-interacting RNAs (piRNAs), are evolutionarily conserved in animals and play important roles in transposon silencing during gametogenesis []. Mammalian Piwi proteins include PIWIL1/Miwi, PIWIL2/Mili, PIWIL3 and PIWIL4/Miwi2.PIWI-like 1 (PIWIL1) is essential for the transition of round spermatid into elongated spermatid [], and also plays a role in the polarisation and radial migration of newborn neurons in the developing cerebral cortex [].
