Hemocytes participate in calcium carbonate crystal formation, transportation and shell regeneration in the pearl oyster Pinctada fucata

• Published in: Fish & shellfish immunology 2016-04, Vol.51, p.263-270
• Main Authors: Li, Shiguo, Liu, Yangjia, Liu, Chuang, Huang, Jingliang, Zheng, Guilan, Xie, Liping, Zhang, Rongqing
• Format: Article
• Language: English
• Subjects: Animal Shells - metabolism; Animals; Biological Transport; Biomineralization; CaCO3 crystal; Calcium Carbonate - metabolism; Granulocytes - metabolism; Hemocyte; Hemocytes - metabolism; Hemocytes - ultrastructure; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Mollusca; Pinctada - metabolism; Pinctada fucata; Shell regeneration
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2016.02.027

In this study, light microscope, scanning and transmission electron microscope, hematoxylin-eosin and fluorescent staining, and mass spectrometry methods were employed to observe the calcium carbonate (CaCO3) crystal formation, hemocyte release and transportation, and hemocyte distribution at the shell regeneration area and to analyse the proteome of hemocytes in the pearl oyster, Pinctada fucata. The results indicated that intracellular CaCO3 crystals were observed in circulating hemocytes in P. fucata, implying that there was a suitable microenvironment for crystal formation in the hemocytes. This conclusion was further supported by the proteome analysis, in which various biomineralization-related proteins were detected. The crystal-bearing hemocytes, mainly granulocytes, may be released to extrapallial fluid (EPF) by the secretory cavities distributed on the outer surface of the mantle centre. These granulocytes in the EPF and between the regenerated shells were abundant and free. In the regenerated prismatic layer, the granulocytes were fused into each column and fragmented with the duration of shell maturation, suggesting the direct involvement of hemocytes in shell regeneration. Overall, this study provided evidence that hemocytes participated in CaCO3 crystal formation, transportation and shell regeneration in the pearl oyster. These results are helpful to further understand the exact mechanism of hemocyte-mediated biomineralization in shelled molluscs. •CaCO3 crystals are observed in circulating hemocytes in Pinctada fucata.•Hemocyte proteome shows the molecular basis for CaCO3 crystal formation.•Crystal-bearing hemocytes may be secreted by secretory cavities on mantle.•Hemocytes directly involve in the regeneration of prismatic layer in P. fucata.