Cloning and tissue-specific expression of mouse macrophage colony-stimulating factor mRNA

Macrophage colony-stimulating factor (CSF-1) stimulates the production of macrophages from bone marrow progenitor cells. We have identified a cDNA clone for murine CSF-1 by antibody screening of a mouse L-cell cDNA library in the expression vector lambda gt11. A screen of about 150,000 recombinant plaques yielded 6 clones that reacted well with an antibody raised against denatured and reduced mouse L-cell CSF-1. These clones were further screened with synthetic oligonucleotides based on the amino-terminal amino acid sequence of CSF-1. One clone, which hybridized to the oligonucleotides, was sequenced and found to contain a single open reading frame. This encompassed 68 amino acids of the mature protein, including the entire amino-terminal sequence we previously reported. This is preceded by what appears to be a 31 amino acid signal peptide. Blot analysis showed that this cDNA hybridizes to a major mRNA species of about 4.5 kilobases (kb) as well as several smaller, less abundant mRNA species (3.8, 2.3, and 1.4 kb) present in mouse L cells. A similar pattern of hybridization was observed with mRNA from a human pancreatic carcinoma cell line that produces CSF-1. Striking differences in the qualitative and quantitative expression of mRNA species for CSF-1 were observed in various mouse tissues. Liver expressed primarily a 1.4-kb species, heart and lung expressed primarily a 4.5-kb species, brain expressed high levels of both the 4.5-kb and 1.4-kb species, and intestine lacked detectable CSF-1 transcripts. Southern blot analysis suggests that the CSF-1 gene is present as a single copy in the mouse haploid genome and that it is not rearranged or amplified in L cells.