EST analysis of gene expression in early cleavage-stage sea urchin embryos

A set of 956 expressed sequence tags derived from 7-hour (mid-cleavage) sea urchin embryos was analyzed to assess biosynthetic functions and to illumi nate the structure of the message population at this stage. About a quarter of the expressed sequence tags represented repetitive sequence transcripts typical of early embryos, or ribosomal and mitochondrial RNAs, while a maj ority of the remainder contained significant open reading frames. A total o f 232 sequences, including 153 different proteins, produced significant mat ches when compared against GenBank, The majority of these identified sequen ces represented 'housekeeping' proteins, i.e., cytoskeletal proteins, metab olic enzymes, transporters and proteins involved in cell division. The most interesting finds were components of signaling systems and transcription f actors not previously reported in early sea urchin embryos, including compo nents of Notch and TGF signal transduction pathways. As expected from earli er kinetic analyses of the embryo mRNA populations, no very prevalent prote in-coding species were encountered; the most highly represented such sequen ces were cDNAs encoding cyclins A and B, The frequency of occurrence of all sequences within the database was used to construct a sequence prevalence distribution. The result, confirming earlier mRNA population analyses, indi cated that the poly(A) RNA of the early embryo consists mainly of a very co mplex set of low-copy-number transcripts.