Expression patterns of Pl-c-jun during Paracentrotus lividus sea urchin development.

Abstract The AP-1 transcription factor is involved in many cellular events such as cell cycle, cell proliferation, differentiation. It consists of dimers composed of different proteins, c-jun, junB, c-fos, Fra-1 and Fra-2. We isolated the complete cDNA encoding the Pl-c-jun gene from P.lividus embryos and described the phylogenetic relationships with homologs of different phyla. We found that Pl-c-jun mRNA levels, measured by QPCR, were high in unfertilized egg, and decreased during development if compared to egg's mRNA. The spatial expression of Pl-c-jun mRNA, detected by WMISH in embryos at different developmental stages, showed ubiquitous transcripts in the cleavage stages. Then, Pl-c-jun mRNA was restricted in a few cells at the vegetative region of blastula and in some skeletogenic cells, the Primary Mesenchyme Cells (PMC), in gastrula and pluteus embryos. The localization of c-jun protein was studied by immunofluorescence experiments on whole mount embryos using commercial antibodies. The presence of total c-jun protein in the PMCs was confirmed, showing a cytoplasmic localization, while its phosphorylated form was restricted to the nucleus of the same cells. Preliminary Western Blot of total c-jun protein, in subcellular fractionation experiments, showed nuclear and cytoplasmic localization too. The specific localization of Pl-c-jun in PMC suggests a role as a regulatory element of skeletogenic genes.