Search

calaxin is a newly identified calcium sensor gene that modulates the movement of flagella (and possibly cilia). It was first identified from the ascidian Ciona intestinalis, and its orthologs have been observed in a wide range of animals and choanoflagellates. However, no calaxin-ortholog in a Lophotrochozoa species has been reported so far. This leaves open the question of whether the modulation of ciliary motility by calaxin is conserved among animals. We report a calaxin gene from the Pacific oyster Crassostrea gigas. This gene, termed cgi-calaxin, possesses three conserved EF-hand motifs as its orthologs from chordates. A phylogenetic analysis confirmed its orthology. Expression analysis revealed high expression in typical ciliated tissues such as gill and hepatopancreas. The spatiotemporal expression of the gene during early development was investigated using whole mount in situ hybridization. The results revealed that cgi-calaxin mRNA was aggregated in ciliated tissues of early larvae such as prototroch and velum. Immunofluorescence experiment further certified the ciliary localization of Cgi-Calaxin protein in D-veligers. We prepared the recombinant protein of cgi-calaxin and proved it had the capacity to bind to calcium. These results support the conserved roles of cgi-calaxin as a calcium sensor in ciliated cells and enrich the current knowledge on regulatory mechanisms of molluscan cilia. Moreover, we found the gene to be expressed in poorly ciliated tissues, such as adductor muscle, indicating possible roles in non-ciliated cells, which merits further investigation. [ABSTRACT FROM AUTHOR]

The Pacific oyster Crassostrea gigasis a potential model organism of bivalve mollusks. Comprehensive studies on the proteome of its sperm are necessary to expand our understanding on its reproduction and development, which however are still poor currently. In this study, to improve the situation, we conducted a proteomic analysis on the sperm based on two-dimensional electrophoresis combined with protein identification through mass spectra data. Fifty-six protein spots with constant and relatively high expression levels were selected for protein identification. Among them, 36 were identified (corresponding to 31 proteins), including cytoskeletal proteins, proteins involved in energy supply, protein modifiers, signal regulators, antioxidant proteins, and others. We proposed that these proteins might play important roles in sperm motility, gamete interaction, and oxidation resistance. In particular, we observed several heat shock proteins that were proved to play essential roles in animal sperms. A further immunofluorescence experiment revealed a mitochondria localization of Hsp60s and wide distributions of Hsp70s, indicating these proteins might function in various processes such as mitochondrial function, gamete interaction, and regulation of receptor activity. Our data will provide fundamental supports for the studies on the mechanisms of fertilization and contribute to expand the understandings on reproduction and development of bivalve mollusks.