ATP-binding cassette (ABC) transporter expression and localization in sea urchin development

Background: ATP‐binding cassette (ABC) transporters are membrane proteins that regulate intracellular concentrations of myriad compounds and ions. There are >100 ABC transporter predictions in the Strongylocentrotus purpuratus genome, including 40 annotated ABCB, ABCC, and ABCG “multidrug efflux” transporters. Despite the importance of multidrug transporters for protection and signaling, their expression patterns have not been characterized in deuterostome embryos. Results: Sea urchin embryos expressed 20 ABCB, ABCC, and ABCG transporter genes in the first 58 hr of development, from unfertilized egg to early prism. We quantified transcripts of ABCB1a, ABCB4a, ABCC1, ABCC5a, ABCC9a, and ABCG2b, and found that ABCB1a mRNA was 10–100 times more abundant than other transporter mRNAs. In situ hybridization showed ABCB1a was expressed ubiquitously in embryos, while ABCC5a was restricted to secondary mesenchyme cells and their precursors. Fluorescent protein fusions showed localization of ABCB1a on apical cell surfaces, and ABCC5a on basolateral surfaces. Conclusions: Embryos use many ABC transporters with predicted functions in cell signaling, lysosomal and mitochondrial homeostasis, potassium channel regulation, pigmentation, and xenobiotic efflux. Detailed characterization of ABCB1a and ABCC5a revealed that they have different temporal and spatial gene expression profiles and protein localization patterns that correlate to their predicted functions in protection and development, respectively. Developmental Dynamics 241:1111–1124, 2012. © 2012 Wiley Periodicals, Inc. Key findings: Twenty ABCB, ABCC, and ABCG genes are expressed during the first 58 hr of sea urchin development. Expressed ABC transporter genes have predicted functions in cell signaling, lysosomal and mitochondrial homeostasis, potassium channel regulation, pigmentation, and xenobiotic efflux. ABCB1a mRNA is 10–100 times more abundant than mRNA of other ABC transporters. ABCB1a is expressed in all cells of the embryo, while ABCC5a is expressed only in mesodermal precursors. ABCB1a protein localizes to the apical membrane of the embryo, while ABCC5a is expressed on basolateral membranes of polarized cells.