Programmed DNA elimination in multicellular organisms.

Genetic information typically remains constant in all cells throughout the life cycle of most organisms. However, there are exceptions where DNA elimination is an integral, developmental program for some organisms, associated with generating distinct germline versus somatic genomes. Programmed DNA elimination occurs in unicellular ciliates and diverse metazoa ranging from nematodes to vertebrates. DNA elimination can occur through chromosome breakage and selective loss of chromosome regions or the elimination of individual chromosomes. Recent studies provide compelling evidence that DNA elimination is a novel form of gene silencing, dosage compensation, and sex determination. Further identification of the eliminated sequences, genome changes, and in depth characterization of this phenomenon in diverse metazoans is needed to shed new light on the functions and mechanisms of this regulated process.