Spatially restricted expression of strim, a novel TRIM-containing gene, in the oral ectoderm of the developing sea urchin embryo Paracentrotus lividus.

The recent wealth of genomic data has confirmed that bilaterians as simple as nematodes and as complex as humans use the same basic toolkit of transcription factors and signaling molecules to process spatial and temporal information during development (1,2). Among these regulators, the TRIM/RBCC (Tripartite motif/RING-Bbox-Coiled Coil) family represents one of the largest classes of putative E3 ubiquitin ligases that play essential roles in cell cycle regulation and development (3). It consists of rapidly evolving genes, identified in eukaryotic organisms (4,5). In the sea urchin Paracentrotus lividus we have identified a locus containing two copies, probably originated from a duplication event, of a gene coding for a TRIM-containing factor that we named strim (sea urchin TRIM). Both genes consist of a single 1839bp-long exon and share extensive sequence similarity. As embryogenesis occurs, zygotic transcription of strim starts at the very early cleavage and reaches its maximum at the morula stage. From the gastrula stage onward, strim expression fades out and very low amounts of mRNA are detectable, by RT-PCR, at prism stage. Very interestingly, whole mount in situ hybridization showed that strim transcripts are asymmetrically localized in the embryo, being restricted exclusively to the oral ectoderm. These results could suggest a role for strim in cell specification of the oral domain.