Abstract
Studies in non-teleost vertebrates have found microRNAs (miRNAs) to be essential for proper gonadal development. However, comparatively little is known about their role during gonadal development in teleost fishes. So far in zebrafish, a model teleost, transcript profiling throughout gonadal development has not been established because of a tiny size of an organ in juvenile stages and its poor distinguishability from surrounding tissues. We performed small RNA sequencing on isolated gonads of See-Thru-Gonad line, from the undifferentiated state at 3 weeks post fertilization (wpf) to fully mature adults at 24 wpf. We identified 520 gonadal mature miRNAs; 111 of them had significant changes in abundance over time, while 50 miRNAs were either testis- or ovary-enriched significantly in at least one developmental stage. We characterized patterns of miRNA abundance over time including isomiR variants. We identified putative germline versus gonadal somatic miRNAs through differential small RNA sequencing of isolated gametes versus the whole gonads. This report is the most comprehensive analysis of the miRNA repertoire in zebrafish gonads during the sexual development to date and provides an important database from which functional studies can be performed.
Highlights
MicroRNAs are a highly conserved class of small regulatory RNAs, approximately 22 nucleotides long, which have a primary function in repressing the post-transcriptional expression of target messenger RNAs[1]
Zebrafish gonads from nine stages of development, as well as gametes (Fig. 1) were sampled and used to prepare a total of 47 small RNA libraries
We detected high abundance of let-7a-5p in testis at 6 wpf (Fig. 4), but not in sexually mature gonads, in contrast to the other four fish species, and the other zebrafish study27. miR202-5p had high abundance in rainbow trout, marine medaka, and the other zebrafish study, but we detected comparatively lower abundance (Fig. 4), similar to Nile tilapia. miR-181a-5p was highly abundant in Nile tilapia and olive flounder, as well as 12 wpf zebrafish ovaries (Fig. 4), but not highly abundant at 24 wpf ovary or in the related zebrafish study
Summary
MicroRNAs (miRNAs) are a highly conserved class of small regulatory RNAs, approximately 22 nucleotides (nt) long, which have a primary function in repressing the post-transcriptional expression of target messenger RNAs (mRNAs)[1]. Several studies have reported differential expression of miRNAs during gonadal development of commercially important teleost species. In yellow catfish (Pylodictis fulvidraco), the miRNA repertoire of immature gonads was determined[24], and in Nile tilapia (Oreochromis niloticus), gonads during sexual differentiation[25] as well as at sexual maturity have been sequenced[26]. While these studies provide important information about the miRNA repertoire during specific stages of development, the findings lack context without a more complete overview of the gonadal miRNA repertoire. A more complete overview of miRNA abundance would be beneficial to understand the role of miRNAs in teleost reproduction
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