The human genome includes many retroelements including the human endogenous retroviruses (HERVs). ERV3, one of the most studied HERVs, is thought to have integrated 30 to 40 million years ago and is present in higher primates with the exception of gorillas. Taken together, the observation of genome conservation, the detection of transcript expression, and the presence of conserved ORFs is circumstantial evidence for a functional role. A functional role is also suggested by the observation that downregulation of ERV3 is reported in choriocarcinoma.
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