Small RNA including microRNA (miRNA) and Piwi-interacting RNA (piRNA) play important roles in germline maintenance and maturation in a wide variety of species. However, relatively little is known about the role of miRNA in male germline maturation in humans and other primates. Here, we focused on rhesus macaques, as a model primate species closely related to humans, to study small RNA expression in testis samples throughout postnatal development and maturation. During testis development, we observe a sharp transition in overall miRNA and piRNA expression levels resulting from a rise in piRNA and a corresponding decrease in miRNA abundance. Unexpectedly, this transition takes place at approximately one year of age – far earlier than rhesus macaque sexual maturation at 4-5 years of age. Although the overall trend is for declining expression, we identified a group of 29 miRNA that show a marked increase in expression in macaque testis at approximately five years of age – the time interval associated with macaque sexual maturation. These miRNA are preferentially expressed in testis and tend to target genes involved in transcriptional regulation, DNA binding, cell migration, embryonic morphogenesisand variety of other functions associated with growth and development. In addition, 14 of these 29 miRNA originate from one primate-specific miRNA cluster. 

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