We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus purpuratus , a model for developmental and systems biology. The sequencing strategy combined whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones, aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome. The genome encodes about 23,300 genes, including many previously thought to be vertebrate innovations or known only outside the deuterostomes. This echinoderm genome provides an evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes.

Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related¹. These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae^2,3,4,5, closely related to the kelps^6,7 (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic² approaches to explore these and other^4,5 aspects of brown algal biology further.

During the past decade, there has been growing interest in the role of translational regulation of gene expression in many organisms. Polysome profiling has been developed to infer the translational status of a specific mRNA species or to analyze the translatome, i.e. the subset of mRNAs actively translated in a cell. Polysome profiling is especially suitable for emergent model organisms for which genomic data are limited. In this paper, we describe an optimized protocol for the purification of sea urchin polysomes and highlight the critical steps involved in polysome purification. We applied this protocol to obtain experimental results on translational regulation of mRNAs following fertilization. Our protocol should prove useful for integrating the study of the role of translational regulation in gene regulatory networks in any biological model. In addition, we demonstrate how to carry out high-throughput processing of polysome gradient fractions, for the simultaneous screening of multiple biological conditions and large-scale preparation of samples for next-generation sequencing.

Globin mRNAs accumulate to 95% of total cellular mRNA during terminal erythroid differentiation, reflecting their extraordinary stability. The stability of human α-globin mRNA is paralleled by formation of a sequence-specific RNA-protein (RNP) complex at a pyrimidine-rich site within its 3′ untranslated region (3′UTR), the α-complex. The proteins of the α-complex are widely expressed. The α-complex or a closely related complex also assembles at pyrimidine-rich 3′UTR segments of other stable mRNAs. These data suggest that the α-complex may constitute a general determinant of mRNA stability. One or more αCPs, members of a family of hnRNP K-homology domain poly(C) binding proteins, are essential constituents of the α-complex. The ability of αCPs to homodimerize and their reported association with additional RNA binding proteins such as AU-rich binding factor 1 (AUF1) and hnRNP K have suggested that the α-complex is a multisubunit structure. In the present study, we have addressed the composition of the α-complex. An RNA titration recruitment assay revealed that αCPs were quantitatively incorporated into the α-complex in the absence of associated AUF1 and hnRNP K. A high-affinity direct interaction between each of the three major αCP isoforms and the α-globin 3′UTR was detected, suggesting that each of these proteins might be sufficient for α-complex assembly. This sufficiency was further supported by the sequence-specific binding of recombinant αCPs to a spectrum of RNA targets. Finally, density sedimentation analysis demonstrated that the α-complex could accommodate only a single αCP. These data established that a single αCP molecule binds directly to the α-globin 3′UTR, resulting in a simple binary structure for the α-complex.