A medaka gonad-specific lncRNA may act as pri-miR-202 to regulate testicular endocrine homeostasis and spermatogenesis.

A large number of long non-coding RNAs (lncRNAs) are expressed in animal gonads, but their functions are poorly understood. In this study, a gonad-specific lncRNA, termed lnc4, was identified and characterized in the model fish medaka (Oryzias latipes). The expression pattern and in vitro functional analyses indicated that lnc4 was likely to be a primary transcript of miR-202 (pri-miR-202). Results of single-molecule fluorescence in situ hybridization demonstrated that the precursor miR-202 (pre-miR-202) was highly expressed in the nuclei of testicular somatic cells, including Leydig and Sertoli cells, whereas only a small amount of lnc4 molecules could be detected co-expressed with pre-miR-202 in Sertoli cells due to its low expression level. Deletion of the lnc4 locus led to a significant reduction in testis size and a dramatic decrease in the number of male germ cells, as well as a reduction in sperm viability. Moreover, lnc4 knockout resulted in enhanced synthesis and secretion of testicular somatic cells and accelerated differentiation of immature male germ cells. Taken together, functional studies of lnc4 and its mature transcript miR-202 will contribute to the understanding of the important role of non-coding RNAs in animal or human reproductive disorders.