GFP of rare codons in fruit fly embryo (IMAGE) Duke University Caption A translucent fruit fly larvae glows where a green fluorescent protein (GFP) is being expressed by codons that are rare in the fly genome. Only two tissues, the brain (left) and testis (right) are capable of expressing this version of GFP. Credit Fox Lab, Duke University Usage Restrictions none License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.