Molecular dissection of germ cell development in the planarian Schmidtea mediterranea

Abstract

Freshwater planarians appear to utilize inductive signals to specify their germ cell lineage: germ cells are believed to form post-embryonically from the pluripotent somatic stem cells, known as neoblasts. Previously, we identified a planarian homolog of nanos (Smed-nanos) and demonstrated by RNA interference (RNAi) that this gene is required for the development, maintenance, and regeneration of planarian germ cells. We have performed microarray analyses to compare gene expression profiles between planarians with early germ cells and those without them. We identified ∼300 genes that are significantly down-regulated in animals lacking early germ cells. This data set contains genes implicated in germ cell development in other organisms, conserved genes not yet reported to have germ cell-related functions, and novel genes. Analysis using putative domain functions (Clusters of Orthologous Groups) suggested diverse molecular functions, including cytoskeletal components, metabolism, RNA processing and modification, transcription, as well as signal transduction. Top hits have been validated by in situ hybridization. Functional analyses of these genes via RNA interference are being carried out. Thus far, we have identified several genes that, when knocked down by RNAi, cause various defects in germ cell development, including: impaired testes development; loss of spermatogonial stem cells; meiotic failure; and defects in sperm elongation. This work will contribute to our knowledge of conserved regulators of germ cell differentiation. (Supported by NIH-NICHD R01-HD043403.)