INTERCELLULAR TRANSFER OF p-GLUCURONIDASE IN CHIMERIC MICE

Chimeric mice were produced by aggregating 2 embryos, each of which was homozygous for a different structural allele of the enzyme /?-glucuronidase. The two alleles used were Gus, the 'wild-type' allele, and Gus, an allele whose gene product shows decreased activity in all tissues as well as decreased heat stability. Staining of untreated adult chimeric livers for glucuronidase activity revealed a mosaic of high (Gus) and low (Gus*) activity cells. The boundaries between cells of different activity were sharp and revealed no diffusion of enzyme or reaction product. Treating sections at 73 °C before staining led to a decay of staining activity in normal (non-chimeric) Gus/Gus and Giis/Gus tissue. The rates of activity loss under the conditions used differed by 10-fold. Of the 2 genotypes in the chimera, the dark-staining, Gus, cells decayed in a fashion similar to that of the Gus/Gus control. The light-staining, Gus, cells of the chimera lost their staining in a unique fashion. Within 20 min they quickly lost a majority of their staining activity but that which remained was relatively heat stable. The second GusMike phase of the decay, seen both photographically and photometrically, suggests that Giis* gene product has been transferred to cells of Gus/Giu genotype.