WYNN, A.*; SHAFER, T.H.; University of North Carolina Wilmington: Four differentially expressed Callinectes sapidus (blue crab) cuticular transcripts containing the Rebers-Riddiford consensus sequence

Decapod crustaceans such as Callinectes sapidus, the blue crab, provide a unique opportunity to study the proteins involved in biomineralization. Subsequent to each molt, the majority of the exoskeleton calcifies while morphologically similar cuticle at the joints remains uncalcified (arthrodial membrane). Several proteins from both types of cuticle contain the chitin-binding Rebers-Riddiford (RR) consensus sequence, Gx8Gx7YxAxExGYx7Px2P. This study obtained sequence and expression data from hypodermal tissue of C. sapidus for four transcripts containing the RR consensus sequence. Expression analysis using Northern blot and quantitative PCR revealed that two of the transcripts, CSAMP8.1 and CSAMP6.0, are found only in arthrodial membrane and expressed uniformly both before and after the molt. Analysis of the remaining two transcripts, CSCP8.5 and CSCP8.2, revealed that both are expressed solely in pre-molt calcified cuticle, indicating possible involvement in the mineralization of the pre-exuvial cuticle. NCBI Blast results for CSAMP8.1 and CSAMP6.0 identified sequence homology with proteins containing the RR consensus sequence found in the uncalcified membranes of Cancer pagarus, Marsupenaeus japonicus, and Homarus americanus. NCBI Blast results for CSCP8.2 and CSCP8.5 identified sequence homology with calcification-associated peptides containing the RR consensus sequence obtained from the calcified cuticle of Procambarus clarkii. These results add C. sapidus to the list of arthropods containing cuticular proteins with the characteristic RR consensus sequence. The differential expression of these four genes is consistent with the hypothesis that RR-containing proteins play an important role in regulating calcification.