miR-218 appears to be a vertebrate specific microRNA and has now been predicted and experimentally confirmed in a wide range of vertebrate species.[1] The extents of the hairpin precursors are not known. In this case the mature sequence in excised from the 5'arm of the hairpin.
miR-218 is specifically expressed by mammalian motor neurons during embryonic development into adulthood, and motor neurons lacking expression of miR-218 exhibit hyperexcitability, neuromuscular junction failure, and neurodegeneration, as demonstrated by knockout mouse models.[2]
The involvement of miR-218 in cancer has also been investigated. miR-218, along with miR-585, has been found to be silenced by DNA methylation in oral squamous cell carcinoma.[3] It is also downregulated in Nasopharyngeal carcinoma, with artificially-induced expression serving to slow tumour growth.[4] miR-218 has also been found to have tumour suppressing qualities in bladder cancer cells.[5] miR-218 expression was associated with overall survival in breast cancer datasets.[6]
^Lánczky A, Nagy Á, Bottai G, Munkácsy G, Szabó A, Santarpia L, Győrffy B (December 2016). "miRpower: a web-tool to validate survival-associated miRNAs utilizing expression data from 2178 breast cancer patients". Breast Cancer Research and Treatment. 160 (3): 439–446. doi:10.1007/s10549-016-4013-7. PMID27744485.