The emerging role of microRNAs in fish ovary: A mini review

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression primarily at the post-transcriptional levels. It is now well established that miRNAs are crucial regulators of many developmental and physiological processes, including reproduction. In teleosts, expression profiling studies have shown that miRNAs are expressed in the fish ovary and their levels are regulated during follicle development and by hormones. Using CRISPR/Cas9 mediated gene knockout strategies, several recent studies have provided strong evidence that miR-202 and miR-200s on chromosome 23 play critical roles in regulating ovarian development, oogenesis, and ovulation. In this mini review, we provide a brief overview of canonical miRNA biogenesis and functions; summarize miRNAs that are expressed in fish ovary; and discuss the emerging role of miRNAs in regulating fish ovarian functions.

Transgenic fluorescent zebrafish lines that have revolutionized biomedical research

Since its debut in the biomedical research fields in 1981, zebrafish have been used as a vertebrate model organism in more than 40,000 biomedical research studies. Especially useful are zebrafish lines expressing fluorescent proteins in a molecule, intracellular organelle, cell or tissue specific manner because they allow the visualization and tracking of molecules, intracellular organelles, cells or tissues of interest in real time and in vivo. In this review, we summarize representative transgenic fluorescent zebrafish lines that have revolutionized biomedical research on signal transduction, the craniofacial skeletal system, the hematopoietic system, the nervous system, the urogenital system, the digestive system and intracellular organelles.

Dynamics of miRNA transcriptome during gonadal development of zebrafish

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.