Structural alterations of the c-myc oncogene in human Burkitt's lymphoma and mouse plasmacytoma suggest that this oncogene is involved in several B cell neoplasms. The possibility of c-myc alterations in human myeloma has not been explored, probably because the low proliferative activity characteristic of this tumor impairs the propagation of representative cell lines for the performance of adequate cytogenetic studies. This report describes alterations in the c-myc locus with concomitant elevated expression of mRNA in the tumor cells of two of 37 patients with multiple myeloma. In one case, somatic cell hybrid studies revealed that the cloned rearranged DNA was entirely derived from chromosome 8, thus indicating a novel mechanism of c-myc activation different from that in Burkitt's lymphoma. Seven other patients exhibited five- to 12-fold overexpression of c-myc RNA when compared with normal marrow cells. Elevated mRNA expression in about one fourth of our patients suggests that the c-myc oncogene has a pathogenetic role in the evolution of multiple myeloma.

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Hybridization of a ³H-labeled bovine glucagon cDNA plasmid to human metaphase chromosomes revealed significant labeling of the distal portion of the long arm of chromosome 2. A large portion (37%) of the cells analyzed exhibited labeling of the 2. A significant percentage (40%) of the labeled sites on the 2 were in segment 2q36→37. Therefore, the human glucagon gene (GCG), was assigned to this segment. Localization of the glucagon gene, whose chromosomal assignment was previously not known, demonstrates the general applicability of in situ hybridization as a powerful gene mapping technique.

Total RNA extracted from peripheral blood lymphocytes of a patient with B-cell chronic lymphocytic leukemia (CLL) and the poly (A+) RNA was purified. A cDNA library was constructed and approximately 4,000 clones were screened in order to identify genes preferentially expressed in CLL. A relatively low repetition frequency characterizes the majority of the abundant mRNA species present in CLL lymphocytes. One clone, corresponding to the mRNA encoding the HLA-DR-associated invariant chain, was selected and its expression was examined in different leukemic cell populations and in normal tissues. DNA-RNA hybridization studies showed that the invariant chain mRNA (In-mRNA) is detectable in RNA preparations from human blood cells and their precursors, whereas no In-mRNA is found in several other tissues examined. Among various normal and leukemic leukocyte populations, the highest levels of In- mRNA are found in CLL. Therefore, a role of In-chain mRNA as a marker of CLL is proposed. Our data support a relationship between high levels of invariant chain mRNA and the out of cycle condition of CLL peripheral blood lymphocytes.