Location: Cool and Cold Water Aquaculture ResearchTitle: Transcriptome analysis of egg viability in rainbow trout Oncorchynchus mykiss
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 9/19/2018
Publication Date: 3/7/2019
Citation: Ma, H., Martin, K., Dixon Iii, D., Weber, G.M. 2019. Transcriptome analysis of egg viability in rainbow trout Oncorchynchus mykiss. Aquaculture America Conference. AAC:3719.
Technical Abstract: Background: Maternal mRNA transcripts are accumulated in the oocyte during oogenesis to provide for protein synthesis from oocyte maturation through early embryonic development, when nuclear transcription is silenced. These maternal transcripts have short poly(A) tails after undergoing post-transcriptional processing necessary for stabilizing the transcripts for storage. The transcripts undergo cytoplasmic polyadenylation when the transcripts are to be translated. Transcriptome analyses comparing total mRNA content and content of elongated poly(A) mRNAs among eggs of different quality can provide insight into molecular mechanism affecting developmental competence of the egg. The present study used RNA-seq to compare transcriptomes of unfertilized eggs of rainbow trout families yielding different eyeing rates, following rRNA-removal and poly(A) capture for construction of the libraries. Results: The percentage of embryos to reach the 32-cell stage at 24 hours post-fertilization was significantly correlated to family eyeing rate, supporting the embryos were developmentally compromised before zygote genome activation. RNA sequencing identified 2 differentially expressed transcripts (DETs) from total mRNA sequencing comparing families with low quality (<5% eyeing), medium quality (30%-50% eyeing), and high quality (>80% eyeing) eggs. In contrast, RNA sequencing from poly(A) capture transcript sequencing identified 945 DETs between low and high-quality eggs, 1012 between low and medium quality eggs, and only 2 between medium and high-quality eggs. The transcripts encoded by mitochondrial genes were enriched in the polyadenylated transcript sequencing and reduced in low quality eggs. Similarly, mitochondrial DNA was reduced in low quality eggs compared with medium and high-quality eggs. The functional gene analysis classified the 945 DETs between low and high-quality eggs into 31 functional modules, many of which were related to ribosome and mitochondrion. The other modules were involved in transcription, translation, cell division, apoptosis, and immune responses. Conclusions: Our results support differences in egg quality deriving from differences in mitochondrial function and maternal nuclear transcript activation and polyadenylation before ovulation, as opposed to accumulation and storage of maternal nuclear transcripts during oogenesis. Transcriptome comparisons support low-quality eggs suffered from inadequacies for oxidative phosphorylation and translation. The differentially expressed transcripts identified in this study provide insight into developmental competence in rainbow trout eggs.