Fig. 3. Co-expression of BRII-myc and HA-BRIa-ca leads to an increase in stimulation of the pSBE-Luc reporter gene activity compared with the single transfection of BRIa-ca. BRIa-ca and BRII-KR do not increase the luciferase activity of the pSBE-Luc. Also co-expression of BRIa-ca and BRII-KR does not result in an increase in luciferase activity, indicating that the kinase activity of BRII is required. Limb mesenchymal cells (isolated from day 11.5 mouse embryos) were transfected with a pSBE-Luc reporter, expression vector containing either of the two receptors and pRLSV40 (normalisation). Cells were plated at high density in the wells of a 24-well tissue culture dish, and 48 hours following transfection cells were lysed and luciferase activity measured.