A microarray-based analysis of oocyte quality in the European clam Ruditapes decussatus

Abstract

Abstract A microarray-based analysis was performed with the objective of describing genomic features of oocytes and looking for potential markers of oocyte quality in the economically important European clam, Ruditapes decussatus . Oocytes of 25 females from Ria de Aveiro, western coast of Portugal (40°42′N; 08°40′W) were selected for this study and oocyte quality was estimated by success of D-larval rate under controlled conditions, which appeared to vary from 0 to 95%. By genome-wide expression profiling with a DNA microarray, 526 probes appeared differentially expressed between two groups representing the largest and smallest value of D larval rates, named good (represented by a mean D-larval yield of 57 ± 22%) and poor (9 ± 5%) quality oocytes. Enrichment analysis showed “lysosome” (dre04142) as the single pathway represented in the enriched KEGG pathway terms, with 8 genes coding for putative cathepsins. Furthermore, differentially expressed genes involved in oocyte protection (DnaJ (Hsp40), Hsp70, cyclophilin B, PDI), maturation (Cam-PDE1C, PRDM9, G protein), sperm–egg interaction (PDI, G protein) and apoptosis (TNF) were also identified. From these, the apoptosis pathway was supposed to assume an important role in oocyte quality as the mRNA level of caspase 8 appeared also negatively correlated with the D-larval yield. Finally, a G-protein transcript was identified as more abundant in poor quality oocytes, which underlines the importance of release prophase I block and meiotic maturation in the oocytes of this species. This study provided new highly valuable information on genes specifically expressed by mature oocytes of R. decussatus , for further understanding of the mechanisms of early development in this species. Statement of relevance Understand the mechanisms of early development in the European clam R. decussatus .