Abstract
BackgroundBlack 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.ResultsThe 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-491) contains supplementary material, which is available to authorized users.
Highlights
Black pearl farming is based on culture of the blacklip pearl oyster Pinctada margaritifera (Mollusca, lophotrochozoa), a protandrous hermaphrodite species
P. margaritifera is a biological model for biomineralization [6,7] and reproduction [8,9]; it is a sentinel species in the context of global change [5] and is economically important for pearl production, a domain in which genetic selection can contribute to quality improvement
Gonad development stage and sex were determined by histological methods and samples were classified into the ten different categories of gonadic tissues described in Figure 1: male and female at “Early” stage, “Intermediate” stage, at “Mature” stage, “Regressed” stage; “Inversion” and “Undetermined”
Summary
Black pearl farming is based on culture of the blacklip pearl oyster Pinctada margaritifera (Mollusca, lophotrochozoa), a protandrous hermaphrodite species. P. margaritifera is a biological model for biomineralization [6,7] and reproduction [8,9]; it is a sentinel species in the context of global change [5] and is economically important for pearl production, a domain in which genetic selection can contribute to quality improvement. It has been shown that the pearl aspect/quality is dependent on the genetics of the graft donor oyster [10]. The aim of the P. margaritifera selection program, is to breed families of graft donor oysters selected for their capacity to produce pearls of quality and/or particular colors and/ or rapid growth [11]. It relies on the knowledge of the underlying physiological mechanisms and factors controlling them [12,13,14]
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