Identification of neuropeptides from eyestalk transcriptome profiling analysis of female oriental river prawn (Macrobrachium nipponense) under hypoxia and reoxygenation conditions.

The oriental river prawn, Macrobrachium nipponense, is a commercial freshwater prawn species in China. It is highly sensitive to hypoxia, and this has posed a challenge to its intensive culturing. To date, the effects of hypoxia on reproduction in female prawns are not entirely clear, as are the underlying mechanisms of the effects of hypoxia. In this work, comparative transcriptome and gene expression analyses of the eyestalk were performed in M. nipponense females under hypoxia and reoxygenation conditions. Sequencing and de novo assembly of the combined reads yielded 43,583 unigenes with an average length of 1726 bp. A total of 711 genes were found to be differentially expressed in the eyestalk under the hypoxia and reoxygenation conditions. With the help of functional and pathway enrichment analysis of the differentially expressed genes, a novel set of transcripts that were associated with several important functions, such as hormone biosynthesis and progesterone-mediated oocyte maturation, were identified. Additionally, ten neuropeptides were identified based on the differentially expressed transcripts, and they were validated by quantitative real-time polymerase chain reaction (qRT-PCR) and reverse transcription PCR (RT-PCR) analyses. Three neuropeptide genes were expressed in the neural tissue and ovary of the prawns; this indicates that they were involved in reproductive processes. In particular, RNA interference (RNAi) short neuropeptide F dramatically promoted ovary maturation, as indicated by the gonad somatic index. While the present findings do indicate that hypoxia affects reproductive function in M. nipponense females, in-depth functional analyses of the candidate neuropeptides should be conducted in the future to understand their role in hypoxia adaptation and the associated mechanisms that affect the reproductive capacity of this species.