The miR-8 microRNA precursor (homologous to miR-141, miR-200, miR-236), is a short non-coding RNA gene involved in gene regulation. miR-8 in Drosophila melanogaster is expressed from the 3' arm of related precursor hairpins (represented here), along with miR-200, miR-236, miR-429 and human and mouse homolog miR-141. Members of this precursor family have now been predicted or experimentally confirmed in a wide range of species. The bounds of the precursors are predicted based on conservation and base pairing and are not generally known. The miR-200 family is highly conserved in bilaterian animals, with miR-8 as the sole homolog in Drosophila. This species has accordingly been used heavily in work looking to uncover the biological function of the miR-200 family. miR-8 has been observed at all developmental stages of the embryo, with a complete absence from cultured S2 cells of D. melanogaster. Its expression has been seen to be strongly upregulated in larvae and this expression then sustained through to adulthood.
The miR-200 family is believed to play an essential role in tumor suppression by inhibiting epithelial-mesenchymal transition (EMT), the initiating step of metastasis (Korpal). EMT occurs as part of embryonic development, and shares many similarities with cancer progression. During EMT, cells lose adhesion and increase in motility. This is characterized by repression of E-cadherin expression, which also occurs during the initial stages of metastasis.