Sequence, annotation and developmental expression of the sea urchin Ca2+-ATPase family

Whole genome sequence data permit the study of protein families regulating cellular homeostasis during development. Here we present a study of the sea urchin Ca2+-ATPases made possible by the Sea Urchin Genome Sequencing Project. This is of potential interest because adult sea urchins, their gametes and embryos live in the relatively high Ca2+ concentration of 10 mM. Three Ca2+-ATPases regulate Ca2+ levels in animal cells: plasma membrane Ca2+-ATPase (PMCA), sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) and secretory pathway Ca2+-ATPase (SPCA). The primary structures of Sp-PMCA and Sp-SERCA in the sea urchin, Strongylocentrotus purpuratus (Sp), have been published. Here, we present the primary structure of Sp-SPCA, which is 912 amino acids and has 66% identity and 80% similarity to human SPCA1. Southern blots and genome analysis show that Sp-SPCA is a single copy gene. Each Sp Ca2+-ATPase is highly conserved when compared to its human ortholog, indicating that human and sea urchin share structurally similar energy driven Ca2+ homeostasis mechanisms that have been maintained throughout the course of deuterostome evolution. Annotation using the assembled sea urchin genome reveals that Sp-SPCA, Sp-PMCA and Sp-SERCA have 23, 17 and 24 exons. RT-Q-PCR shows that transcripts of Sp-SPCA are at low levels compared to Sp-PMCA and Sp-SERCA. Gradual increases in Sp-PMCA and Sp-SERCA mRNA begin at the 18 hour hatched blastula stage and peak 4-5-fold higher by 25 h at the mid to late blastulae stage.