Transcriptome analysis reveals key molecular events of germinal vesicle breakdown inSipunculus nudus

Abstract

Germinal vesicle (GV) breakdown (GVBD) is an important event in the maturation of oocytes. This process is also a prerequisite for the fertilization of many invertebrates. In Sipunculus nudus, the gonads cannot be observed with the naked eye. Oocytes develop freely in the coelomic fluid and separated easily. Thus, they are a good material for studying invertebrate GVBD. We isolated and obtained samples of oocytes from GV and GVBD phases of S. nudus and constructed two oocyte transcriptomes. Transcriptome analysis identified 14,170 differentially expressed unigenes (DEUs). Gene Ontology (GO) enrichment analysis showed that 69 GO terms were significantly enriched, and 6 GO terms including integral component of membrane (GO: 0016021), nuclearus (GO: 0005634), protein kinase activity (GO: 0004672), protein tyrosine phosphatase activity (GO: 0004725), spindle pole (GO: 0000922) and microtubule organizing center (GO: 0005815) were closely related to GVBD. We identified 31 DEUs associated with the GVBD process including M-phase inducer phosphatase 2 (CDC25B), 5-hydroxytryptamine receptor (5-HTR) and calcium-transporting ATPase sarcoplasmic/endoplasmic reticulum type (SERCA). The results support the view that hormonal action, calcium regulation, phosphorylation and spindle microtubule action may participate in the process of GVBD. This research presented the development process of S. nudus oocytes and provided valuable materials for the GVBD in other invertebrates.