The Macrostomum lignano EST database as a molecular resource for studying platyhelminth development and phylogeny

We report the development of an Expressed Sequence Tag (EST) resource for the flatworm Macrostomum lignano. This taxon is of interest due to its basal placement within the flatworms. As such, it provides a useful comparative model for understanding the development of neural and sensory organization. It was anticipated on the basis of previous studies e.g., Sánchez-Alvarado et al., Development, 129:5659–5665, (2002)] that a wide range of developmental markers would be expressed in later-stage macrostomids, and this proved to be the case, permitting recovery of a range of gene sequences important in development. To this end, an adult Macrostomum cDNA library was generated and 7,680 Macrostomum ESTs were sequenced from the 5′ end. In addition, 1,536 of these aforementioned sequences were sequenced from the 3′ end. Of the roughly 5,416 non-redundant sequences identified, 68% are similar to previously reported genes of known function. In addition, nearly 100 specific clones were obtained with potential neural and sensory function. From these data, an annotated searchable database of the Macrostomum EST collection has been made available on the web. A major objective was to obtain genes that would allow reconstruction of embryogenesis, and in particular neurogenesis, in a basal platyhelminth. The sequences recovered will serve as probes with which the origin and morphogenesis of lineages and tissues can be followed. To this end, we demonstrate a protocol for combined immunohistochemistry and in situ hybridization labeling in juvenile Macrostomum, employing homologs of lin11/lim1 and six3/optix. Expression of these genes is shown in the context of the neuropile/muscle system.