LACK OF CORRELATION BETWEEN C-MYC EXPRESSION AND PROGRAMMED OR EXPERIMENTALLY-INDUCED CELL-DEATH DURING CHICK LIMB DEVELOPMENT

The protooncogene c-myc positively regulates cell death in most in vit ro cell model systems under conditions of restricted proliferation, an d it has been proposed that cell death is a physiological function of c-myc. To investigate possible changes in c-myc expression concomitant with programmed cell death, we have analyzed c-myc mRNA expression du ring chick limb development. Expression of c-myc was high in the premu scular masses at earlier stages and in the chondrogenic condensations at later stages of limb development, as demonstrated by in situ mRNA h ybridization in sections and whole-mount. However, we did not detect c -myc expression in specific limb areas where massive apoptosis was occ urring. Furthermore, when the apical ridge was removed from stage 20 w ing buds, there was no increase in the expression of c-myc in the subr idge mesoderm, despite the extensive cell death induced by this surgic al manipulation. Therefore, our results show no correlation between el evated c-myc expression and either programmed or experimentally-induce d apoptosis in the developing limb. These results argue against a role of c-myc in cell death occurring in vivo.