Fig. 7. The relationship between LIF-STAT3, GSK3ß and Myc in maintenance of ES cell self-renewal. Following LIF withdrawal, Myc transcriptional activity collapses, GSK3ß is activated and Myc becomes phosphorylated at T58, triggering its ubiquitin (u)-mediated, proteosome-dependent degradation. `?' indicates the possible role of pathways involved in (1) suppression of GSK3ß activity or (2) pathways of transcriptional control that collaborate with LIF to control Myc transcription. The latter could involve signals generated by serum-derived growth factors. The involvement of LIF/STAT3-Myc independent pathways are also indicated.