A primate-specific microRNA enters the lung cancer landscape

Characterization of the lung cancer genome through unbiased next-generation sequencing has led to the discovery of new driver somatic mutations (1, 2) and gene fusions (3). Lung cancers show the second highest prevalence of somatic mutations among all cancer types, and a mutation profile that reflects the effect of chronic exposure to tobacco carcinogens, the main risk factor etiologically associated with this disease (2⇓–4). The next chapter of genomic decoding, through small RNA sequencing, brings about the discovery of primate-specific microRNAs (miRNAs) of the airway epithelium and the intriguing possibility that some may function as lung tumor suppressors (5). miRNAs were first discovered and investigated in 1993 by Ambros and colleagues and Ruvkun and colleagues (6, 7) in the course of studies on developmental timing of Caenorhabditis elegans. Despite their recent historical account, miRNA-mediated posttranscriptional control of protein-coding genes is an evolutionarily ancient mechanism that regulates key developmental processes in eukaryotes. With the degree of granularity afforded by deep sequencing technologies, the number of expressed sequences showing evidence of a characteristic miRNA hairpin structure keeps rising. The 20th edition of miRBase, the catalog of miRNA sequences, released in June 2013, contains more than 24,000 entries for hairpin precursor miRNAs. Surprisingly, with more miRNA sequences revealed comes the realization that an astounding nearly 30% of them are unique to primates, and even a few, such as miR-941, may be unique …