Evolution Research - General Evolution News

Scientists have identified a group of genes that control the formation of shapes and colour patterns on the shell of the tropical marine mollusc referred to as 'abalone' (info). A study published in the open access journal BMC Biology reveals that the shape and colour patterns on the shell of the mollusc mirror the localised expression of specific genes in the mantle, a layer of skin situated just below the shell. The authors of the study identify one gene in particular that controls the formation of blue dots on the shell of the mollusc.

Daniel Jackson, Bernard Degnan and colleagues from the University of Queensland, Australia, collaborated with colleagues from the Department of Geobiology at the University of Gottingen, Germany to analyse gene expression in the tropical abalone Haliotis asinina (Images). They sequenced 530 randomly-selected genes expressed in the mantle tissue of the young abalone.

Continued at "Patterns On Tropical Marine Mollusk Shell Mirror Gene Expression Patterns"
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Based on the open access BMC Biology paper "A rapidly evolving secretome builds and patterns a sea shell"

Abstract (Provisional*):

Background

Instructions to fabricate mineralized structures with distinct nanoscale architectures, such as seashells and coral and vertebrate skeletons are encoded in the genomes of a wide variety of animals. In mollusks, the mantle is responsible for the extra-cellular production of the shell, directing the ordered biomineralization of CaCO3 and the deposition of architectural and color patterns. The evolutionary origins of the ability to synthesize calcified structures across various metazoan taxa remain obscure, with only a small number of protein families identified from molluskan shells. The recent sequencing of a wide range of metazoan genomes coupled with the analysis of gene expression in non-model animals has allowed us to investigate the evolution and process of biomineralization in gastropod mollusks.

Results

Here we show that over 25% of the genes expressed in the mantle of the vetigastropod Haliotis asinina encode secreted proteins, indicating that hundreds of proteins are likely to be contributing to shell fabrication and patterning. Almost 85% of the secretome encodes novel proteins; remarkably only 19% of these have identifiable homologues in the full genome of the patellogastropod Lottia scutum. The spatial expression profiles of mantle genes that belong to the secretome is restricted to discrete mantle zones, with each zone responsible for the fabrication of one of the structural layers of the shell. Patterned expression of a subset of genes along the length of the mantle is indicative of roles in shell ornamentation. For example, Has-sometsuke maps precisely to pigmentation patterns in the shell, providing the first case of a gene product to be involved in molluskan shell pigmentation. We also describe the expression of 2 novel genes involved in nacre (mother of pearl) deposition.

Conclusions

The unexpected complexity and evolvability of this secretome, and the modular design of the molluskan mantle enables diversification of shell strength and design, and as such must contribute to the variety of adaptive architectures and colors found in mollusk shells. The composition of this novel mantle-specific secretome suggests that there are significant molecular differences in the ways in which gastropods synthesize the shell.

* "The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production."

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