EXPRESSION OF BETA-GALACTOSIDASE UNDER THE CONTROL OF THE HUMAN C-MYCPROMOTER IN TRANSGENIC MICE IS INHIBITED BY MITHRAMYCIN

In order to assess the functional contribution of the human c-myc prom oter region in the expression of the c-myc gene, transgenic mouse line s containing a bacterial lac Z gene encoding beta-galactosidase under the control of the human c-myc protooncogene promoter were generated. Transgenic mouse embryos heterozygous for the human c-myc Z transgene demonstrate high amounts of beta-galactosidase activity as early as da y 11 of embryogenesis by histochemical staining of whole embryos using -bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) as substra te, localizing specifically to early spinal cord tissue. beta-galactos idase activity can be demonstrated by histochemical staining in brain tissue of day 14 embryos, localizing mainly to the prefrontal cortex r egion, while relative amounts of beta-galactosidase in spinal cord tis sue are reduced. Determination of specific activity of beta-galactosid ase using resorufin-beta galactopyranoside as substrate in homogenates of whole embryos heterozygous for the human c-myc/lac Z transgene dem onstrates significantly elevated beta-galactosidase activity over cont rol embryos in day 11 and day 14 embryos. Surprisingly, cell homogenat es of brain tissue from adult G(1) generation mice heterozygous for th e human c-myc/lac Z transgene demonstrate greater than 10-foId higher specific activity of beta-galactosidase over normal control brain tiss ue. Specific inhibition of the c-myc/lac Z transgene was also demonstr ated in developing embryos using mithramycin given at a dose of 150 mu g kg(-1) d(-1) intraperitoneal to pregnant females on days 7-13 of ge station. Both histochemical staining of beta-galactosidase and specifi c activity assays of day 14 embryos demonstrated significantly lower l evels of beta-galactosidase than untreated controls. These results are unique since we are able to detect expression of beta-galactosidase i n developing embryonic central nervous system tissue along with adult brain tissue of animals carrying the human c-myc Z transgene and we ar e able to specifically inhibit expression of the transgene using mithr amycin administered in utero.