Mouse spleen and IgD-secreting plasmacytomas contain multiple IgD δ chain RNAs

Immunoglobulin gene expression requires that cells combine the correct genetic information by DNA rearrangement and RNA processing to produce mature, translatable mRNAs. The mechanisms that operate to produce IgD heavy chain (δ chain) mRNA are thought to be especially complex1–3. Like other immunoglobulins, IgD exists in membrane and secreted forms4,5. By analogy with results of studies of μ6–10and γ11,12gene expression, we expected that δ chains would also be encoded by two different mRNAs, containing common sequence information transcribed from constant region gene segments but different information transcribed from coding sequences located 3′ to the constant region gene segments. Instead, we identified13more than two δ mRNAs in normal mouse spleen and in two IgD-secreting plasmacytomas14, TEPC 1017 and TEPC 1033. Now we have used 32P-labelled DNA fragments prepared from a δ cDNA clone15and a δ genomic clone16to characterize by hybridization these δ RNAs, fractionated on methyl mercury hydroxide agarose gels. We find that normal mouse spleen contains a major 2.9-kilobase (kb) and a minor 2.1-kb RNA encoding membrane-bound δ chains (δm) and that TEPC 1017 and TEPC 1033 contain similar δmRNAs plus a 1.75-kb RNA encoding secreted δ chains (δm). We have also observed less abundant δ RNA species (2.65 and 3.2 kb). Different gene segments or combinations of segments are used in the 3′ termini of the multiple δ RNAs.