Mouse‐specific up‐regulation of Ccnb1 expression by miR‐199a‐5p in keratinocyte

MicroRNA (miRNA) are a class of single‐stranded, small non‐coding RNA that regulate various biological processes, including skin and hair cycle regulation, by modulating the expression of specific genes at the post‐transcriptional level. Recently, several studies reported that miRNA directly or indirectly up‐regulate target genes. Previously, we performed microarray analysis to identify the target genes of miR‐199a‐5p in a mouse skin keratinocyte cell line and detected more than 200 genes whose expression was significantly increased by miR‐199a‐5p overexpression (> 1.5‐fold). In this study, we further investigated these genes and found that cyclin B1 (Ccnb1) expression was positively regulated by miR‐199a‐5p in keratinocyte. Moreover, Ccnb1 expression was inversely correlated with miR‐199a‐5p expression during the mouse hair cycle. Cell cycle analysis showed that the proportion of cells in S phase was slightly increased, while the proportion of cells in G2/M phase decreased by miR‐199‐5p. Using luciferase assay, we found that the 3′ untranslated region of Ccnb1 was a direct target of miR‐199a‐5p. We also found that the regulation of Ccnb1 expression by miR‐199a‐5p is mouse specific. CCNB1 expression was not affected in the human and monkey cell lines. These results provide a new relationship between Ccnb1 and miR‐199a‐5p in both mouse keratinocyte and miRNA biology.