Dataset Information

Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera.

ABSTRACT: The bivalve Pinctada margaritifera exhibits three main transplant phenotypes derived from the donor (from which a mantle graft tissue, the saibo, is excised), the recipient (into which the saibo is implanted with a nucleus, leading to the formation of a pearl sac "chimera") and the cultured pearls themselves. This first phenome study on the species derived from a large experimental graft. Transplant phenotype was assessed at three scales: 1) macro, pearl size, colour, grade, 2) micro, pearl surface microstructure, and 3) molecular, biomineralisation gene expression level in saibo and pearl sac tissues. From donor to pearl, the phenome revealed fine variations of quality traits dependent on the position on the mantle where the saibo was cut, whose variation could overlap with inter-individual donor phenotype differences. A single donor phenotype could therefore produce multiple pearl phenotypes at the scale of the saibo position, mirroring its original activity at the mantle position level and the colour and shape of the shell. This phenome study provides essential information on phenotypic trait architecture enabling us to explore and explain the main biological functions and pave the way for a phenomic project on P. margaritifera that could benefit the pearl industry.

SUBMITTER: Ky CL

PROVIDER: S-EPMC5794767 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera.

Ky Chin-Long CL Quillien Virgile V Broustal Floriane F Soyez Claude C Devaux Dominique D

Scientific reports 20180201 1

The bivalve Pinctada margaritifera exhibits three main transplant phenotypes derived from the donor (from which a mantle graft tissue, the saibo, is excised), the recipient (into which the saibo is implanted with a nucleus, leading to the formation of a pearl sac "chimera") and the cultured pearls themselves. This first phenome study on the species derived from a large experimental graft. Transplant phenotype was assessed at three scales: 1) macro, pearl size, colour, grade, 2) micro, pearl surf ...[more]

PMID: 29391512

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Project description:BackgroundColor 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.ResultsOut 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.ConclusionsOur 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.

Project description:The genomics of economically important marine bivalves is studied to provide better understanding of the molecular mechanisms underlying their different reproductive strategies. The recently available gonad transcriptome of the black-lip pearl oyster Pinctada margaritifera is a novel and powerful resource to study these mechanisms in marine mollusks displaying hermaphroditic features. In this study, RNAseq quantification data of the P. margaritifera gonad transcriptome were analyzed to identify candidate genes in histologically-characterized gonad samples to provide molecular signatures of the female and male sexual pathway in this pearl oyster. Based on the RNAseq data set, stringent expression analysis identified 1,937 contigs that were differentially expressed between the gonad histological categories. From the hierarchical clustering analysis, a new reproduction model is proposed, based on a dual histo-molecular analytical approach. Nine candidate genes were identified as markers of the sexual pathway: 7 for the female pathway and 2 for the male one. Their mRNA levels were assayed by real-time PCR on a new set of gonadic samples. A clustering method revealed four principal expression patterns based on the relative gene expression ratio. A multivariate regression tree realized on these new samples and validated on the previously analyzed RNAseq samples showed that the sexual pathway of P. margaritifera can be predicted by a 3-gene-pair expression ratio model of 4 different genes: pmarg-43476, pmarg-foxl2, pmarg-54338 and pmarg-fem1-like. This 3-gene-pair expression ratio model strongly suggests only the implication of pmarg-foxl2 and pmarg-fem1-like in the sex inversion of P. margaritifera. This work provides the first histo-molecular model of P. margaritifera reproduction and a gene expression signature of its sexual pathway discriminating the male and female pathways. These represent useful tools for understanding and studying sex inversion, sex differentiation and sex determinism in this species and other related species for aquaculture purposes such as genetic selection programs.

Project description:BACKGROUND:Black pearl farming is based on culture of the blacklip pearl oyster Pinctada margaritifera (Mollusca, lophotrochozoa), a protandrous hermaphrodite species. At first maturation, all individuals are males. The female sex appears progressively from two years old, which represents a limitation for broodstock conditioning for aquaculture production. In marine mollusks displaying hermaphroditic features, data on sexual determinism and differentiation, including the molecular sex determining cascade, are scarce. To increase genomic resources and identify the molecular mechanisms whereby gene expression may act in the sexual dimorphism of P. margaritifera, we performed gonad transcriptome analysis. RESULTS:The gonad transcriptome of P. margaritifera was sequenced from several gonadic samples of males and females at different development stages, using a Next-Generation-Sequencing method and RNAseq technology. After Illumina sequencing, assembly and annotation, we obtained 70,147 contigs of which 62.2% shared homologies with existing protein sequences, and 9% showed functional annotation with Gene Ontology terms. Differential expression analysis identified 1,993 differentially expressed contigs between the different categories of gonads. Clustering methods of samples revealed that the sex explained most of the variation in gonad gene expression. K-means clustering of differentially expressed contigs showed 815 and 574 contigs were more expressed in male and female gonads, respectively. The analysis of these contigs revealed the presence of known specific genes coding for proteins involved in sex determinism and/or differentiation, such as dmrt and fem-1 like for males, or foxl2 and vitellogenin for females. The specific gene expression profiles of pmarg-fem1-like, pmarg-dmrt and pmarg-foxl2 in different reproductive stages (undetermined, sexual inversion and regression) suggest that these three genes are potentially involved in the sperm-oocyte switch in P. margaritifera. CONCLUSIONS:The study provides a new transcriptomic tool to study reproduction in hermaphroditic marine mollusks. It identifies sex differentiation and potential sex determining genes in P. margaritifera, a protandrous hermaphrodite species.

Dataset Information

Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera.

Publications

Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera.

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