Comparative Analysis and Identification of Differentially Expressed microRNAs in the Hypothalamus of Kazakh Sheep Exposed to Different Photoperiod Conditions

MicroRNAs (miRNA) plays an important role in several mammalian biological regulatory processes by post-transcriptionally regulating gene expression. However, there is little information on the miRNAs involved in the photoperiodism pathway that controls seasonal activity. To enhance our knowledge on the effect of different photoperiod conditions on miRNA, we divided Kazakh sheep into two groups: one exposed to a long photoperiod (LP, 16L:8D) and another with exposed to a short photoperiod (SP, 8L:16D) under supplemental feeding conditions. Further we compared the related miRNAs and target genes between the two groups. Fifteen differentially expressed miRNAs were identified, which were associated with 310 regulatory pathways covering photoperiodism, reproductive hormones, and nutrition. The miR-136-GNAQ pair was selected and validated as a differentially expressed, and a dual-luciferase reporter assay showed that the negative feedback loop existed between them. Examination of the expression profile revealed that the GNAQ expression was low in the estrous females both under LP and SP conditions, but high expression of GNAQ was observed in the anestrous females under LP conditions. Moreover, functional analysis revealed that KISS1 and GnRH expression was upregulated when GNAQ expression was downregulated in the hypothalamic cells, whereas DIO2 and TSHB expression was downregulated. Thus, miR-136-GNAQ might act as a switch in the regulation of seasonal estrus under different photoperiod conditions. These findings further enrich our understanding of the relationship between miRNAs and seasonal regulation of reproductive activity. Furthermore, our study provides novel insights into the miRNA-mediated regulatory mechanisms for overcoming photoinhibition in the seasonally breeding mammals, such as Kazakh sheep.