Molecular characterization of CHST11 and its potential role in nacre formation in pearl oyster Pinctada fucata martensii

Background: C4ST-1 catalyzes the transfer of sulfate groups in the sulfonation of chondroitin during chondroitin sulfate synthesis. Chondroitin sulfate consists of numerous copies of negatively charged sulfonic acid groups that participate in the nucleation process of biomineralization. In the present study, we obtained two CHST11 genes (PmCHST11a and PmCHST11b) which encoded the C4ST-1 and explored the functions of these genes in the synthesis of chondroitin sulfate and in the formation of the nacreous layer of shells. Results: Both PmCHST11a and PmCHST11b had a sulfotransferase-2 domain, a signal peptide and a transmembrane domain. These properties indicated that these genes localize in the Golgi apparatus. Real-time PCR revealed that both PmCHST11a and PmCHST11b were highly expressed in the central zone of the mantle tissue. Inhibiting PmCHST11a and PmCHST11b via RNA interference significantly decreased the expression levels of these genes in the central zone of the mantle tissue and the concentration of chondroitin sulfate in extrapallial fluid. Moreover, shell nacre crystallized irregularly with a rough surface after RNA interference. Conclusions: This study indicated that PmCHST11a and PmCHST11b are involved in the nacre formation of Pinctada fucata martensii through participating in the synthesis of chondroitin sulfate.

Biomineralization: Some complex crystallite-oriented skeletal structures.

The present review focuses on some specific aspects of biomineralization with regard to the evolution of the first focused visioning systems in trilobites, the formation of molluscan shell architecture, dental enamel and its biomechanical properties and the structure of the calcified amniote egg, both fossil and recent. As an interdisciplinary field, biomineralization deals with the formation, structure and mechanical strength of mineralized skeletonized tissue secreted by organisms. Mineral matter formed in this way occurs in all three domains of life and consists of several mineral varieties, of which carbonates, phosphates and opaline silica are the most common. Animals and plants need mechanical support to counteract gravitational forces on land and hydrostatic pressure in the deep ocean, which is provided by a skeletonized framework. Skeleton architecture mainly consists of basic elements represented by small usually micrometer- to nanometer-sized crystallites of calcite and aragonite for carbonate systems and apatite crystallites for phosphatic ones, and then these building blocks develop into structured more complex frameworks. As selective pressures work towards optimizing stress and response, the orientation, morphology and structural arrangement of the crystallites indicates the distribution of the stress field of the biomineralized tissue. Large animals such as the dinosaurs have to deal with large gravitational forces, but in much smaller skeletonized organism such as the coccoliths, a few micrometer in diameter made up of even smaller individual crystallites, van der Waals forces play an increasingly important role and are at present poorly understood. Skeleton formation is dependent upon many factors including ambient water chemistry, temperature and environment. Ocean chemistry has played a vital role in the origins of skeletonization, 500 to 600 million years (ma) ago with the dominance of calcium carbonate as the principal skeleton-forming tissue and with phosphates and silica as important but secondary materials. The preservation of calcareous skeletons in deep time has resulted in providing interesting information: for example, the number of days in the Devonian year has been established on the basis of well-preserved lunar (annual) cycles, and isotope chemistry has led to an elaborate protocol for using O18/O16 stable isotopes for palaeotemperature measurements in the geological past. Stable isotopes of dental apatite have helped to establish ecological shifts (terrestrial to wholly marine) during the evolution of the Cetacea. Biomineralization as a field of specialization is still searching for its own independent identity, but gradually, its importance is being realized as a model for engineering applications especially at the nanometer scale.