Revealing Mytilus galloprovincialis transcriptomic profile during ontogeny

Mediterranean mussels are a worldwide spread bivalve species with extraordinary biological success. One of the reasons of this success could be the reproduction strategy of bivalves, characterized by the presence of trochophore larvae. Larval development in bivalves has been a topic of raising interest in the scientific community but it deserves much more attention. The principal objective of this work was to study the transcriptomic profile of the ontogeny of M. galloprovincialis analyzing the gene expression in different developmental stages, from oocytes to seed. For this purpose, after conducting a 454 sequencing of transcriptome of mussel hemocytes, adult tissues and larvae, a new DNA microarray comprising sequences of was designed and developed. The studied developmental stages: unfertilized oocytes, veliger (3 days post fertilization; dpf) and pediveliger (20dpf) larvae, settled juveniles (25dpf) and seed (30dpf), showed very different transcriptomic profiles and clustered in groups defining their characteristic gene expression along ontogeny. Mature mussels were obtained from a commercial shellfish farm in Vigo (NW Spain) during the spawning season. Mussels spawning and larval rearing was performed as detailed in Balseiro et al., 2013. Biological replicates were taken at each developmental stage: oocytes, veliger, pediveliger, settled and seed. Total RNA isolation was conducted following the manufacturer’s specifications in combination with the RNeasy Mini kit (Qiagen) for RNA purification after DNase I treatment. Next, the concentration and purity of the RNA were measured using a NanoDrop ND1000 spectrophotometer. Finally, RNA integrity was tested on an Agilent 2100 Bioanalyzer (Agilent Technologies). Only the samples with high RNA quality and quantity were used for labeling and hybridization. 3 to 5 biological replicates were used for each developmental stage and trochophore samples were discarded due to the low RNA integrity.