We examined the distribution of mRNAs for differentiation-stimulating factor (D-factor)/leukemia inhibitory factor (LIF) receptor in various mouse tissues by Northern blotting. A mouse cDNA fragment encoding the D-factor receptor was prepared by the RT-PCR method using human cDNA sequences as primers. The smallest mRNA (3 kb) was present in the liver, but not detectable in other tissues examined. Larger mRNAs (5 and 10 kb) were present in the placenta and the M1 cells, and also detectable in the liver, kidney, heart, lung, brain and embryos. Expression of 3 kb mRNA in the liver increased during pregnancy, being 20 times the initial level on day 15. D-factor receptor cDNAs were isolated from a cDNA library prepared from the liver of a pregnant mouse. Most of the cDNA clones encoded a soluble receptor. A cDNA probe specific for the cellular receptor did not hybridize with 3 kb mRNA in the liver. These results suggest that 3 kb mRNA encodes a soluble D-factor receptor and that the liver is the primary site of synthesis of this soluble receptor.
