Characterization Of Specific miRNAs Involved In Maternal-Zygotic Transition In Rainbow Trout Embryos (Oncorhynchus mykiss)

Maternal-zygotic transition (MZT) is a critical stage for normal embryonic development. During MZT, maternal transcript clearance and zygotic genome activation are highly regulated. In order to identify specific miRNAs that regulate MZT in rainbow trout, we analyzed miRNA transcriptome profiles in different stage embryos. A total of 8 egg/embryo samples including unfertilized egg, 3 hpf (hours post fertilization), 7.5 hpf, 10.5 hpf, 3 dpf (days post fertilization), 6 dpf, 16 dpf, and 24 dpf embryos were collected and small RNAs isolated from these samples were subjected to deep sequencing using the Illumina platform. Over 20 million mappable sequences from each stage sample were produced, from which 760, 352, 347, 313, 396, 481, 600 and 577 known miRNAs were identified, and 325, 411, 91, 308, 45, 478, 187, 360 and 347 novel miRNAs were predicted, respectively. miRNAs of the miR-430 (a, b, c, d, and i) and miR-200 (a and b) families were specifically expressed in 3 dpf and 6 dpf embryos. In addition, 14 novel miRNAs showed high expression in the embryos from 3 hpf to 6 dpf. A total of 784 target genes of these specifically expressed miRNAs were predicted. Gene ontology enrichment analysis showed that most of the target genes are involved in metabolic and biosynthetic processes, as well as in regulation of biological process. Understanding the key miRNAs that regulate MZT during early development may ultimately lead to the development of new strategies to improve egg quality and developmental potential of early embryos in rainbow trout.