Co-expression of full-length and truncated Ig mu-chains in human B lymphocytes results from alternative splicing of a single primary RNA transcript.
A survey of Ig synthesis among mu-heavy chain-producing human B cell lines indicated that roughly one-third co-express full length (mu+) and a particular type of truncated mu-chain (designated mu'). The relative molecular size of the intracellular form of this truncated mu-chain and its normal pattern of N-glycosylation suggested that mu'-chains were missing a single Ig domain at the protein level. Cell-free translation of polyA+ RNA from mu'-producing human B cell lines generated appropriate mu'-translation products, and Northern blot analysis demonstrated the presence of correspondingly truncated mu'-transcripts in these lines. These results pointed to a pretranslational basis for mu+/mu' co-expression. Sequencing of mu+- and mu'-cDNA clones from two human B cell lines showed that mu+- and mu'-transcripts derive from the same primary transcript, with mu'-mRNA formed by a direct leader-to-C mu 1 exon splice such that the heavy chain variable region exon is excluded via a cassette-type alternative splicing mechanism. Southern blot analysis of the rearranged Ig heavy chain genes in one B cell line confirmed that the co-expressed mu+- and mu'-mRNA derive from the same rearranged Ig heavy chain gene. mu'-cDNA clones were readily isolated from normal human bone marrow lymphocytes, whereas peripheral B cells do not appear to express mu'-transcripts. The frequent occurrence of mu'-mRNA in B cell lines, and its high relative expression in untransformed bone marrow lymphocytes attest to a mode of post-transcriptional control of Ig gene expression that may have implications for human B cell development.
Caldwell
J
J
Department of Microbiology and Immunology, Wake Forest University Medical Center, Winston-Salem, NC 27103.
McElhone
P
P
Brokaw
J
J
Anker
R
R
Pollok
B A
BA
D001402:B-Lymphocytes / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000032:analysis; D015321:Gene Rearrangement; D006801:Humans; D007148:Immunoglobulin mu-Chains / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016133:Polymerase Chain Reaction; D012326:RNA Splicing; D014158:Transcription, Genetic
D007148:Immunoglobulin mu-Chains; D004247:DNA