Molecular Correlates of Programmed DNA Elimination

The sea lamprey (Petromyzon marinus: a vertebrate) undergoes reproducible programmed genome rearrangements (PGRs) that mediate the deletion of ~20% of its germline DNA during the development of somatic cell lineages. The genomic differentiation of germline and soma that results from PGR is intriguing from an evolutionary and developmental standpoint because the germline plays a unique role in an organism’s biology. Specifically, the germline must retain the ability to undergo meiotic recombination and the capacity to differentiate into every cell type (pluripotency), whereas these same factors can potentially disrupt genome integrity or cell fate specification if misexpressed in somatic cells. The programmatic elimination of genes is conceptualized as a means of resolving fundamental genetic tradeoffs between germline and soma. Here, we present results from several recent studies that shed new light on the cellular/developmental mechanisms that mediate programmed genome rearrangement, focusing on subcellular morphology, correlated epigenetic changes and a novel class of small RNAs. With its highly dynamic genome biology, lamprey presents a novel evolutionary and developmental model for studying mechanisms of genome stability/instability, biological functions that are unique to pluripotent cell lineages, and fundamental genetic tradeoffs between germline and soma.