Abstract
Calcium (Ca2+) is a ubiquitous intracellular messenger, controlling a diverse range of cellular processes, including fertilization and development of the embryo. One of the key mechanisms involved in triggering intracellular calcium release is the generation of the second messenger inositol-1,4,5-phosphate (IP3) by the phospholipase C (PLC) class of enzymes. Although five distinct forms of PLC have been identified in mammals (, , , , and ), only one, PLC, has thus far been detected in echinoderms. In the present study, we describe the isolation of a cDNA encoding a novel PLC isoform of the delta () subclass, PLC-su, from the egg of the Pacific purple sea urchin Strongylocentrotus purpuratus. We also demonstrate the presence of this PLC within the sperm and in the early embryo. The PLC-su cDNA (2.44 kb) encodes a 742 amino acid polypeptide with an open reading frame of 84.6 kDa and a pI of 6.04. All of the characteristic domains found in mammalian PLC isoforms (PH domain, EF hands, an X–Y catalytic region, and a C2 domain) are present in PLC-su. A homology search revealed that PLC-su shares most sequence identity with bovine PLC2 (39%). We present evidence that PLC-su is expressed in unfertilized eggs, fertilized eggs, and in the early embryo. In addition to Northern and polymerase chain reaction (PCR) analyses, in situ hybridization experiments further demonstrated that the embryonic regions within which the PLC-su transcript can be detected during early embryonic development are associated with the highest levels of proliferative activity, suggesting a possible involvement with metabolism or cell cycle regulation.
