Differential localization of mRNAs during early development in the mollusc, Crepidula fornicata.

Certain mRNAs have been shown to be segregated in different cells in various metazoan embryos. These events represent aspects of autonomous mechanisms that establish particular embryonic cell fates and axial properties associated with asymmetric cell divisions. The spiralian lophotrochozoans (which include molluscs, annelids, nemerteans, gnathostomulids, dicyemid mesozoans, entoprocts, and platyhelminthes) exhibit a highly conserved pattern of early development that involves stereotypical, asymmetric cell divisions (termed "spiral cleavage"). Recently, it was demonstrated that various mRNAs are dynamically localized to the centrosomes in specific cells during early development in the gastropod mollusc, Ilyanassa obsoleta. During subsequent cell divisions, these messages become segregated in particular daughter cells, and it has been proposed that these events distinguish the developmental potential of these cells within the early embryo of I. obsoleta. The molecular mechanisms underlying these events, however, are still unknown. Here we show for the first time in another spiralian lophotrochozoan (the gastropod Crepidula fornicata) that similar patterns of mRNA localization take place during early development. To characterize the transcriptome of early development, and identify candidate genes for the expression analyses, high-throughput sequencing was carried out, via GS FLX Titanium 454 pyrosequencing. The annotated sequences have been made available as a resource for the scientific community (www.life.illinoi.edu/henry/crepidula_databases.html). Presumably, specific proteins associated with centrosomes may be important for these mRNA localization events. In silico sequence comparisons with known centriolar/centrosomal, ciliary/basal body proteomes shows that a large number of those proteins are represented in the collection of expressed sequence tags of C. fornicata annotated in this study. These data should be useful for future studies of the role of specific mRNAs in controlling cell fate and axial specification in the spiralian Lophotrochozoa, and for dissecting the underlying molecular mechanisms that accomplish these events.