Involvement of Hox genes in shell morphogenesis in the encapsulated development of a top shell gastropod (Gibbula varia L.)
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Regulatory gene expression during the patterning of molluscan shells has only recently drawn the attention of scientists. We show that several Hox genes are expressed in association with the shell gland and the mantle in the marine vetigastropod Gibbula varia (L.). The expression of Gva-Hox1, Gva-Post2, and Gva-Post1 is initially detected in the trochophore larval stage in the area of the shell field during formation of embryonic shell. Later, during development, these genes are expressed in the mantle demonstrating their continuous role in larval shell formation and differentiation of mantle edge that secretes the adult shell. Gva-Hox4 is expressed only late during the development of the veliger-like larva and may also be involved in the adult shell morphogenesis. Additionally, this gene also seems to be associated with secretion of another extracellular structure, the operculum. Our data provide further support for association of Hox genes with shell formation which suggest that the molecular mechanisms underlying shell synthesis may consist of numerous conserved pattern-formation genes. In cephalopods, the only other molluscan class in which Hox gene expression has been studied, no involvement of Hox genes in shell formation has been reported. Thus, our results suggest that Hox genes are coopted to various functions in molluscs.
KeywordsGastropod Hox genes Shell morphogenesis Trochophore larva Veliger larva
The authors are grateful to two anonymous reviewers for their constructive comments. We are thankful to Achim Meyer at the Johannes Gutenberg University of Mainz, Germany for his advice with collecting and rearing of animals and to Prof. Michael Akam and Dr. Joakim Eriksson for offering LS the opportunity of training in expression experiments at University Museum of Zoology, University of Cambridge, UK. LS was supported by an EC fellowship within the MOLMORPH network under the 6th Framework Programme “Marie Curie Fellowships for Early Stage Research Training (EST) (Contract number MEST-CT-2005 - 020542).
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