title: Identification of genes associated with shell color in the black-lipped pearl oyster, Pinctada margaritifera.
abstract: BACKGROUND
  Color polymorphism in the nacre of pteriomorphian bivalves is of great interest for the pearl culture industry. The nacreous layer of the Polynesian black-lipped pearl oyster Pinctada margaritifera exhibits a large array of color variation among individuals including reflections of blue, green, yellow and pink in all possible gradients. Although the heritability of nacre color variation patterns has been demonstrated by experimental crossing, little is known about the genes involved in these patterns. In this study, we identify a set of genes differentially expressed among extreme color phenotypes of P. margaritifera using a suppressive and subtractive hybridization (SSH) method comparing black phenotypes with full and half albino individuals.
  
  
  RESULTS
  Out of the 358 and 346 expressed sequence tags (ESTs) obtained by conducting two SSH libraries respectively, the expression patterns of 37 genes were tested with a real-time quantitative PCR (RT-qPCR) approach by pooling five individuals of each phenotype. The expression of 11 genes was subsequently estimated for each individual in order to detect inter-individual variation. Our results suggest that the color of the nacre is partially under the influence of genes involved in the biomineralization of the calcitic layer. A few genes involved in the formation of the aragonite tablets of the nacre layer and in the biosynthesis chain of melanin also showed differential expression patterns. Finally, high variability in gene expression levels were observed within the black phenotypes.
  
  
  CONCLUSIONS
  Our results revealed that three main genetic processes were involved in color polymorphisms: the biomineralization of the nacreous and calcitic layers and the synthesis of pigments such as melanin, suggesting that color polymorphism takes place at different levels in the shell structure. The high variability of gene expression found within black phenotypes suggests that the present work should serve as a basis for future studies exploring more thoroughly the expression patterns of candidate genes within black phenotypes with different dominant iridescent colors.
authors.affiliation: Laboratoire d'Excellence "CORAIL", USR 3278 CNRS-CRIOBE- EPHE, Perpignan, France, Papetoai, Moorea, French Polynesia. sarah.lemer@gmail.com.|Present address: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA. sarah.lemer@gmail.com.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lemer
authors.affiliation: Ifremer, UMR 241 EIO, Laboratoire d'Excellence "CORAIL", BP 7004, 98719, Taravao, Tahiti, French Polynesia. Denis.Saulnier@ifremer.fr.
authors.forename: Denis
authors.initials: D
authors.lastname: Saulnier
authors.affiliation: Ifremer, UMR 241 EIO, Laboratoire d'Excellence "CORAIL", BP 7004, 98719, Taravao, Tahiti, French Polynesia. Yannick.gueguen@ifremer.fr.|Present address: Ifremer, UMR 5244 IHPE, UPVD, CNRS, Université de Montpellier, CC 80, F-34095, Montpellier, France. Yannick.gueguen@ifremer.fr.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Gueguen
authors.affiliation: Laboratoire d'Excellence "CORAIL", USR 3278 CNRS-CRIOBE- EPHE, Perpignan, France, Papetoai, Moorea, French Polynesia. planes@univ-perp.fr.
authors.forename: Serge
authors.initials: S
authors.lastname: Planes
mesh_terms: D000818:Animals; D003116:Color; D020224:Expressed Sequence Tags; D005786:Gene Expression Regulation; D060734:Nacre / Q000235:genetics*; D010641:Phenotype; D049911:Pinctada / Q000235:genetics*
chemical_list: D060734:Nacre