The Analysis of Lineage-Specific Gene Activity During Sea Urchin Development

Abstract

The experimental approach presented here aims to understand the mechanisms by which differential genomic expression is first established in the various spatial domains of the sea urchin embryo. In terms of regulatory organization, the sea urchin and most invertebrate taxa share a general form of embryogenesis in which cell lineage plays an important role. Regions upstream of genes whose expression patterns identify particular embryonic territories are used to construct in vitro reporter genes, which are easily injected into sea urchin embryos. Various reporter gene constructs are utilized to identify regulatory domains of the territorial marker genes. By experimentally altering the sequences in the regulatory domains, we can ascertain the functional relationship among the components. Because sea urchin embryos are easily obtained in large quantity, a straightforward strategy for the biochemical isolation of their nuclear proteins has proved successful. Techniques including affinity chromatography, gel mobility assays, and protein gel blots probed with DNA fragments permit the direct isolation and identification of proteins that specifically bind to segments of the regulatory domains. When interpreted against a background of cell lineage and fate, the mechanisms of transcriptional regulation thus revealed produce a vertically integrated explanation of blastomere specification in the early sea urchin embryo.

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