CD44 and cancer: It has been demonstrated that TG2 is specifically expressed in more aggressive mesenchymal (CD44+) GSCs, but not in less aggressive proneural GSC subtype, in which TG2 can be induced by aldehyde dehydrogenase 1A3 (a retinaldehyde dehydrogenase) and retinoic acid, opening new possible strategies to fight this type of cancer [109].