Identification and molecular characterization of a complement C3 molecule in a lophotrochozoan, the Hawaiian bobtail squid Euprymna scolopes.

Examination of the EST database of the light organ of the Hawaiian bobtail squid Euprymna scolopes revealed a sequence with similarity to complement C3. RACE yielded the full open reading frame of this protein. Analysis of the resultant sequence revealed that Es-C3 (E. scolopes-C3) has conserved residues and domains known to be critical for C3 function. The gene encoding C3 was expressed in all tissues tested, indicating that its expression is widely distributed throughout the animal's body. Immunocytochemistry using an antibody against Es-C3 revealed that the protein is produced principally in the apical surfaces of epithelial cells. The finding of the gene encoding C3 in this mollusk extends the occurrence of this molecule to the lophotrochozoans, demonstrating that complement genes occur in all major branches of the animal kingdom.