ABSTRACT: Mndal, a new interferon-inducible family member, is highly polymorphic, suppresses cell growth and may modify plasmacytoma susceptibility. The human HIN-200 gene cluster and its mouse counterpart, the Interferon inducible-200 (Ifi200) family, both on Chr 1, are associated with several diseases, including solid tumors and lupus. Our study was initiated to identify the modifier gene(s) encoded by the Pctm locus, in which mouse B cell plasmacytomas induced by pristane are associated with heterozygosity of Chr 1 genes near the Ifi200 cluster. A screen for differentially expressed genes in granulomatous tissues induced by pristane in resistant and susceptible strains identified a new Ifi200 member whose expression was 1000-fold higher in the strain carrying the resistant allele of Pctm, and was the most highly expressed Ifi200 gene. The gene, designated Mndal (for MNDA-like, myeloid nuclear differentiation antigen like), was absent in the susceptible genome, as were genomic sequences upstream of Ifi203, the gene adjacent to Mndal. Ectopic expression of MNDAL suppressed cell growth, which, together with the disease susceptibility of heterozygotes at the Pctm locus, suggests that Mndal, perhaps with Ifi203, acts as a tumor suppressor and display(s) haplo-insufficiency. Mndal is highly polymorphic among inbred mouse strains, as it is absent in 10/24 strains. This polymorphism may have implications for other disease modifiers mapping to the same region. Experiment Overall Design: Using institutionally approved animal protocols, mice were given 0.5 ml TMPD intraperitoneally. Three and 18 days later, total RNA was extracted from mesentery of experimental/control animals, using TRIzol (Invitrogen). Labeled aRNA prepared from 1 µg of RNA (MessageAmpII aRNA Amplification kit, Ambion protocols) was hybridized to mouse genome 430 2.0 array chips, processed on Workstation 450, and analyzed with Gene Chip Operating Software (GCOS; Affymetrix). Differential expression was assessed by ANOVA (Partek Genomics Suite).
