title: A shell regeneration assay to identify biomineralization candidate genes in mytilid mussels.
abstract: Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix.
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany; GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Hüning
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Skadi M
authors.initials: SM
authors.lastname: Lange
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Kirti
authors.initials: K
authors.lastname: Ramesh
authors.affiliation: Macquarie University, Sydney, Australia.
authors.forename: Dorrit E
authors.initials: DE
authors.lastname: Jacob
authors.affiliation: Georg-August Universität, Göttingen, Germany.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Jackson
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Panknin
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Magdalena A
authors.initials: MA
authors.lastname: Gutowska
authors.affiliation: Christian-Albrechts Universität, Kiel, Germany.
authors.forename: Eva E R
authors.initials: EE
authors.lastname: Philipp
authors.affiliation: Christian-Albrechts Universität, Kiel, Germany.
authors.forename: Philip
authors.initials: P
authors.lastname: Rosenstiel
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
authors.forename: Magnus
authors.initials: M
authors.lastname: Lucassen
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany. Electronic address: fmelzner@geomar.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Melzner
mesh_terms: D060105:Animal Shells / Q000502:physiology*; D000818:Animals; D002113:Calcification, Physiologic; D023281:Genomics / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D049880:Mytilus edulis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D010865:Pilot Projects; D060888:Real-Time Polymerase Chain Reaction; D012038:Regeneration; D013059:Spectrum Analysis, Raman; D059467:Transcriptome
keywords: Biomineralization; Mytilus; Shell regeneration; Transcriptomics