IDENTIFICATION OF MITOCHODRIAL GENOME-ENCODED SMALL RNAS RELATED TO EGG QUALITY DETERIORATION CAUSED BY POST-OVULATORY AGING IN RAINBOW TROUT    

Numerous factors have been reported to affect rainbow trout egg quality, among which, post-ovulatory aging is one of the most significant causes as reared rainbow trout do not usually volitionally oviposit the ovulated eggs. Frequent examination of the stock is therefore required in order to reduce overtime retention of the eggs in the female abdominal cavity; however, some females are not correctly identified as having ovulated.  In order to uncover the genetic regulation underling egg deterioration caused by post-ovulatory aging in rainbow trout, mitochondrial genome encoded small RNA fragments were analyzed for unfertilized eggs on Day 1, Day 7, and Day 14 post-ovulation with fertilization rates of 91.8%, 73.4%, and less than 50%, respectively.

A total of 248 mitochondrial genome-encoded small RNAs (mitosRNAs) were identified from Illumina high throughput sequencing of libraries constructed from Day 1, Day 7, and Day 14 eggs. Ninety-eight of the small RNAs exhibited more than a three-fold difference in expression between eggs from females exhibiting low and high fertilization rates. RT-qPCR analysis was carried out for 14 randomly selected differentially expressed mitosRNAs, for which 12 were confirmed to be consistent with the sequencing reads. The identified mitosRNAs can potentially serve as biomarkers for egg quality. Further characterization of the differentially expressed mitosRNAs would increase our understanding of mechanisms involved with deterioration of egg quality caused by post-ovulatory aging in rainbow trout.