How mothers program sons to use their Y chromosomes

In many species, maternally deposited Piwi-interacting RNAs (piRNAs) deliver intergenerational epigenetic information to protect progeny from transposon expansion or invasion. However, Y-chromosome-encoded piRNAs cannot be passed from mothers to male offspring, yet mothers use autosomally encoded piRNAs to allow sons to utilize their Y chromosome to protect against 'selfish' elements.