PTEN negatively regulates phospho-inositide 3-kinase (PI3K) signalling and is frequently mutated in human cancers. Because complete deletion of PTEN is embryonic lethal in most model organisms, studying its biological role has been challenging. Choorapoikayil et al. studied the consequences of reduced PTEN expression using mutant zebrafish (which naturally express two functional Pten genes). They find that zebrafish lacking three of the four normal Pten alleles are viable but develop hemangiosarcomas (aggressive tumours of blood vessel origin), mainly close to the eye. These data introduce a new zebrafish model of hemangiosarcoma and expand knowledge on the role of PTEN in endothelial cells. Page 241

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