Abstract
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.
Highlights
The black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758) var. cumingi (Jameson, 1901) is a benthic bivalve occurring in subtropical and tropical coral reefs
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
The most significant outcomes of our study are the two models we constructed allowing us to improve our understanding of the specific reproduction of the marine bivalve P. margaritifera
Summary
The black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758) var. cumingi (Jameson, 1901) is a benthic bivalve occurring in subtropical and tropical coral reefs. Cumingi (Jameson, 1901) is a benthic bivalve occurring in subtropical and tropical coral reefs. The black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758) var. It is widely distributed in the Indo-Pacific region: throughout the Equatorial zone, down to Northern Australia and extending up to the south of Japan [1]. Genetic selection programs have been encouraged because it was demonstrated that the pearl quality is dependent on the genetics of the graft donor oyster [3]. The aim of the P. margaritifera selection program, is to breed families of graft donor oysters selected for their capacity to produce high quality pearls and/or particular colors and/or rapid growth [4,5,6]
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