Cracking the Shell: An Investigation of Shell Repair in the Oyster, Crassostrea virginica

Mollusc shell formation has been an intriguing phenomenon for decades and current research efforts represent a paradigm shift in how oyster shell formation occurs. The older model of shell formation suggests a lack of cellular components as transport vectors for organic and mineral components. However, current research focuses on the potential role of oyster blood cells, hemocytes, in moving organic and mineral components to the shell formation front. A protein biomarker, the amino acid L-3,4-dihydroxyphenylalanine (L-DOPA), is unique to the proteins involved in insoluble organic matrix formation. Tracking the location and temporal occurrence of L-DOPA-containing proteins reveals the potential role of cells in shell repair. Three notch-repair experiments were conducted: a short term 36-hour notch-repair study, a mid-term 7-day notch-repair study, and a long term 8-week notch-repair study. At discrete time intervals, selected oyster compartments of hemocytes, mantle tissues, hemolymph, and nascent shell were sampled to determine the spatial and temporal distributions of the DOPA biomarker. Preliminary results show an increase in DOPA concentration in hemolymph from 0 to 48 hours. Conversely, hemocytes show a decrease in DOPA over time, with the greatest amount of DOPA present at 0 hours and a subsequent decrease over the course of repair. Additionally, nascent shell was analyzed during the 8-week study through the use of scanning electron microscopy (SEM). Analysis of the shell surface showed haphazard crystal formation under normal mineral deposition with crystals irregular in size, shape, and general placement. Newly formed shell from a notched specimen at 48 and 96 hours after notching; however, is characterized by directional and more uniformly shaped crystals. Together these results suggest that hemocytes are selectively shuttling and releasing protein resources to areas of shell repair and provide additional support for the cellular mediated shell formation model, where hemocytes play an active role in materials transport