Developmental functions of piRNAs and transposable elements: a Drosophila point-of-view.

The primary function of the piRNA pathway is to repress the expression and transposition of transposable elements. However, the piRNA pathway has additional biological and developmental functions. These functions are either a consequence of transposon regulation, or they result from direct roles of transposable elements in chromosome structure and gene regulation through piRNAs. Recent data have extended the functions of transposable elements in gene regulation, revealing a trans-acting role of transposable element piRNAs in the control of gene expression. Over the last few years, extensive studies on the piRNA pathway have rapidly increased our understanding of the relationships between transposable elements and the host genome, and of the essential role of transposable elements in biological and developmental processes.