ACTB and melanoma: To this end, we implanted B16.F10 murine melanoma cells into C57BL/6 mice that carry the Xbp1-Venus fusion transgene under the control of the cytomegalovirus (CMV)-β actin promoter, known as the ER stress-activated indicator (ERAI) [41], which reports IRE1α-mediated XBP1 splicing through the expression of the fluorescent Venus protein.