Abstract
Deletions in chromosome 7 of the mouse affect the expression of the metallothionein gene Mt-1, which maps on chromosome 8, and steady-state levels of Mt-1 mRNA are reduced to 15-40% of normal in livers of newborn mice homozygous for either the c3H or c14CoS deletion. Glucocorticoids fail to induce hepatic Mt-1 mRNA levels in deletion homozygotes in contrast to normal littermates. However, zinc chloride is effective in inducing Mt-1 mRNA levels in livers of deletion homozygotes as well as of their normal littermates. Other tissues (e.g., kidney and intestine) of deletion homozygotes express basal levels of Mt-1 mRNA higher than those of normal littermates. In the intestine these are furthermore inducible by both hormonal and metal agents. Thus, loss of inducibility of the Mt-1 gene in deletion homozygotes concerns glucocorticoids only and is furthermore restricted to specific cell types (i.e., hepatocytes). The trans-acting factor(s) normally encoded in the deleted region of chromosome 7 appears to be instrumental in conferring on the metallothionein gene in hepatocytes the essential competence to respond to hormonal inducing signals.