Maternal transcript profiles associated with egg viability in rainbow trout, Oncorhynchus mykiss, and comparisons among populations

Authors: Weber, Gregory - Greg; Birkett, Jill; MARTIN, KYLE - Troutlodge, Inc; DIXON,II, DOUG - Troutlodge, Inc; Gao, Guangtu; Leeds, Timothy - Tim; Vallejo, Roger; Ma, Hao

Submitted to: Aquaculture America
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Markers that can serve as predictors of egg quality and for diagnosing problems with embryo production would benefit fish hatcheries. Since transcription is arrested in the late-stage oocyte the maternal transcriptome stored in the oocyte provides nearly all the mRNA required for oocyte maturation, fertilization, and early cleavage of the embryo. The transcriptome of the unfertilized egg has therefore been targeted to identify informative markers and levels of specific transcripts have been shown to associate with various measures of egg quality. However, these differentially expressed genes (DEGs) have not been consistent among studies. As a start to determining factors that contribute to disparate results among studies, we compared expression of 65 select transcripts previously reported to be potential markers of egg quality in rainbow trout, among three populations. Transcript identified as DEGs from unfertilized eggs of different quality based on eyeing rate were compared among two year classes of the same line (A1, A2) and a population from a different hatchery (B) using an assay based on the nCounter analysis data system (Nanostrings Technologies; Seattle, WA). Most of the genes in the assay, 54, are DEGs from a transcriptome analysis of egg viability using RNA-Seq and fish from Group A1. A total of 32 transcripts were identified as DEGs among the three groups by regression analysis. As could be expected, Group A1 had the most DEGs, 26. Group A2 had 15 DEGs and 14 were shared with A1. Group B which included fish from a different population than the fish from which most of the transcripts were first identified as potential markers of egg quality, had the least DEGs, 12. Seven of the 12 DEGs in Group B overlapped with A1 or A2, and six of these transcripts, dcaf11, impa2, mrpl39_like, senp7, tfip11 and uchl1, were found in all three groups. Our results indicate DEGs for egg quality can overlap among populations of rainbow trout and therefore maternal transcripts found to be differentially expressed between low- and high-quality eggs in one population can be of value for use in other populations, at least when using the same criteria for egg quality. The pattern of transcripts differentially expressed with egg quality remain consistent among year classes of the same line supporting value to line specific DEG discovery efforts. On the other hand, less similarity in dysregulated transcripts among lines than within year classes of the same line suggests patterns of transcriptome dysregulation may provide insight into causes of decreased viability within a hatchery population. Although many DEGs were confirmed, there is considerable variability in transcript abundance among eggs of similar quality for each of the genes and low correlations between transcript abundance and eyeing rate. These factors make it difficult to predict the quality of a single batch of eggs based on transcript abundance of just a few genes.