Directors Seminar: From soma to germ line: how a novel gene became indispensable for reproduction

How novel genes arise in the genome, whether and how they become incorporated into existing gene regulatory networks, and how they can evolve to acquire novel functional over time, are open questions in evolutionary biology. We have used the insect gene oskar as a case study to examine these issues. oskar was first identified and described in the fruit fly Drosophila melanogster for its indispensable role in the germ line and for posterior patterning. In this and likely in other holometabolous insects, oskar assembles germ plasm, a maternally provided cytoplasmic determinant that specifies germ cells. However, a role for oskar in the nervous system, rather than in the germ line, is what appears to be conserved between Drosophila and a basally branching hemimetabolous insect, the cricket Gryllus bimaculatus (Gb). To understand the origins of this novel gene, and the mechanisms underlying the evolution of its function, we have applied functional genetics, biochemistry, bioinformatics and behavioral assays. We discuss evidence regarding the genesis of the novel oskar gene, the biochemical changes in Oskar protein that may have contributed to the evolution of its germ plasm role, and the molecular mechanism of its function in cricket learning and memory.

Cassandra Extavour is a Professor in the Department of Organismic and Evolutionary Biology at Harvard University. Her laboratory is interested in understanding early embryonic development, the genes that control this, the evolutionary origin of those genes and how their functions have changed over evolutionary time. Because of the critical role of germ cells not only in development but also in evolution, her work has primarily focused on germ cell development in a comparative context, using a range of arthropod systems.