MicroRNAs (miRNAs) are a class of non-coding single-stranded RNA molecules, about 22 nucleotides in length, and highly conserved in evolution. They participate in a variety of important biological processes, including the development, differentiation, and apoptosis of eukaryotes. Recent studies have discovered that miRNAs play important roles in the development of primordial germ cells, spermatogenesis, and the process of fertilization.