Mollusk shell formation is a fascinating aspect of biomineralization research. Shell matrix proteins play crucial roles in the control of calcium carbonate crystallization during shell formation in the pearl oyster, Pinctada fucata. Characterization of biomineralization-related genes during larval development could enhance our understanding of shell formation. Genes involved in shell biomineralization were isolated by constructing three suppression subtractive hybridization (SSH) libraries that represented genes expressed at key points during larval shell formation. A total of 2,923 ESTs from these libraries were sequenced and gave 990 unigenes. Unigenes coding for secreted proteins and proteins with tandem-arranged repeat units were screened in the three SSH libraries. A set of sequences coding for genes involved in shell formation was obtained. RT-PCR and in situ hybridization assays were carried out on five genes to investigate their spatial expression in several tissues, especially the mantle tissue. They all showed a different expression pattern from known biomineralization-related genes. Inhibition of the five genes by RNA interference resulted in different defects of the nacreous layer, indicating that they all were involved in aragonite crystallization. Intriguingly, one gene (UD_Cluster94.seq.Singlet1) was restricted to the ‘aragonitic line’. The current data has yielded for the first time, to our knowledge, a suite of biomineralization-related genes active during the developmental stages of P.fucata, five of which were responsible for nacreous layer formation. This provides a useful starting point for isolating new genes involved in shell formation. The effects of genes on the formation of the ‘aragonitic line’, and other areas of the nacreous layer, suggests a different control mechanism for aragonite crystallization initiation from that of mature aragonite growth.
Background:The microstructure of nacre is controlled by the proteins in them. Results: When PfN23 was knocked down, the shell formation in adults and larvae was suppressed.
Conclusion:The basic protein PfN23 is important for the control of crystal growth in nacre. Significance: This might provide a valuable complementary to the classic view that acidic proteins control nacre formation.
Background: Thermodynamically unstable magnesium calcite is deposited in the shell of pearl oysters at ambient pressure. Results: The novel acidic matrix protein PfN44 interacts with magnesium to inhibit the deposition of aragonite. Conclusion: PfN44 participates in shell formation by inhibiting aragonite formation. Significance: Results of this study suggest a connection between the matrix protein and magnesium.
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