Abstract
BackgroundEarly development of an oviparous organism is based on maternally stocked structural, nutritional and regulatory components. These components influence the future developmental potential of an embryo, which is referred to as egg quality. Until zygotic genome activation, translational activity in a fish early embryo is limited to parentally inherited transcripts only. In this study, we asked whether egg transcriptome is associated with egg quality in Atlantic salmon (Salmo salar), which is capable of storing ovulated eggs in its abdominal cavity for a long time before spawning.ResultsWe analyzed messenger RNA (mRNA) and micro RNA (miRNA) transcriptomes throughout the post-ovulatory egg retention period in batches of eggs from two quality groups, good and poor, classified based on the future developmental performance. We identified 28,551 protein-coding genes and 125 microRNA families, with 200 mRNAs and 5 miRNAs showing differential abundance between egg quality groups and/or among postovulatory ages. Transcriptome dynamics during the egg retention period was different in the two egg quality groups. We identified only a single gene, hepcidin-1, as a potential marker for Atlantic salmon egg quality evaluation.ConclusionThe overlapping effect of post-ovulatory age on intrinsic egg developmental competence makes the quantification of egg quality difficult when based on transcripts abundance only.
Highlights
Development of an oviparous organism is based on maternally stocked structural, nutritional and regulatory components
After excluding low-count reads (< 1 Reads per kilobase million (RPKM)) and counting at gene level, 28,551 genes were annotated as conserved messenger RNA (mRNA), which is 48.4% of non-repeat associated loci of salmon genome
Maternal micro RNA (miRNA) targets We found 13,365 Atlantic salmon Expressed sequence tag (EST) with 3’3′ untranslated region (UTR) sequences
Summary
Development of an oviparous organism is based on maternally stocked structural, nutritional and regulatory components These components influence the future developmental potential of an embryo, which is referred to as egg quality. In addition to inherited DNA epigenetic features [2, 3], mature oocytes contain components essential for further embryonic development These essential nutrients, maternal RNAs and proteins are acquired to oocytes in the course of maturation process [4]. Majority of ray-finned fish species ovulate mature oocytes into an ovarian lumen or directly into abdominal cavity, where they are stored until spawning. This postovulatory retention period varies in teleosts from hours to weeks, depending on species, and the deterioration in oocyte developmental competence progresses in time [7]. In Atlantic salmon (Salmo salar), postovulatory aging shows the effect on Bizuayehu et al BMC Genomics (2019) 20:315 egg developmental competence after 2-week retention [10]
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