Transcriptomic features of Pecten maximus oocyte quality and maturation

Abstract

The king scallop Pecten maximus is a high valuable species of great interest in Europe for both fishery and aquaculture. Notably, there has been an increased investment to produce seed for enhancement programmes of wild scallop populations. However, hatchery production is a relatively new industry and it is still underdeveloped. Major hurdles are spawning control and gamete quality. In the present study, a total of 14 scallops were sampled in the bay of Brest (Brittany, France) to compare transcriptomic profiles of mature oocytes collected by spawning induction or by stripping. To reach such a goal, a microarray analysis was performed by using a custom 8x60K oligonucleotide microarray representing 45,488 unique scallop contigs. First we identified genes that were differentially expressed depending on oocyte quality, estimated as the potential to produce D-larvae. Secondly, we investigated the transcriptional features of both stripped and spawned oocytes. Genes coding for proteins involved in cytoskeletal dynamics, serine/threonine kinases signalling pathway, mRNA processing, response to DNA damage, apoptosis and cell-cycle appeared to be of crucial importance for both oocyte maturation and developmental competence. This study allowed us to dramatically increase the knowledge about transcriptional features of oocyte quality and maturation, as well as to propose for the first time putative molecular markers to solve a major bottleneck in scallop aquaculture.

Fig 1. D-larval rates.

Values of D-larval rates of released oocytes (REL) expressed as percentages of trochophore at 48 hpf on the total count of oocytes employed for the fertilization. Standard deviation refers to batch replicates (n = 3) as described in [20].

Fig 2. Enrichment analysis of transcripts significantly correlated with D-larval rates.

Significant enriched BP_direct terms obtained through the enrichment analysis performed on the transcripts significantly correlated with D-larval rates. The green bars identify the number of the correlated genes belonging to the annotation term. Only terms with minimum gene counts of 5 were reported. Numbers beside the bars correspond to the Fold Enrichment reported for each term.

Fig 3. Correlation between gene expression and D-larval rates.

Values of fluorescence reported for probes encoding HUS1, CASP2, GLO1, SIRT1 and PDIA4. Samples are reported in the x axis. Expression level (principal y axis) is expressed in terms normalized fluorescence. The D-larval rate is reported in term of percentage (secondary y axis) and described by a blue line.

Fig 4. Enrichment analysis of DEGs between stripped and released oocytes.

Significant enriched BP_direct terms obtained through the enrichment analysis performed on DEGs between STR and REL oocytes. The orange bars identify the number of the correlated genes belonging to the annotation term. Only terms with minimum gene counts of 5 were reported. Numbers beside the bars correspond to the Fold Enrichment reported for each term.

Fig 5. Main processes affecting oocyte quality.

Genes positively and negatively correlated with D-larval rates were reported in green and in red colour, respectively.