SURROGATE LIGHT CHAIN-DEPENDENT SELECTION OF IG HEAVY-CHAIN-V REGIONS

Bone marrow B cell precursors frequently rearrange the Ig heavy chain variable (V-H) gene segment V(H)81X, It is puzzling, therefore, that m ature B cells in adult mice rarely express mu-heavy chains bearing thi s V-H gene segment, We show in this work in transformed pre-B cell lin es that two V(H)81X/mu-chains that differ in their V-H-D-J(H) joining sequences are not assembled covalently with the B cell precursor-speci fic surrogate light (SL) chain and are not expressed on the cell surfa ce, From these findings, we propose that a B cell precursor clonally e xpands and proceeds to the next developmental stage only if it express es a mu-chain with a V-H domain that, together with the SL chain, dire cts the formation of a signal-transducing mu/SL chain membrane complex , Therefore, a checkpoint exists early in B cell development, at which SL chain not only screens B cell precursors for the presence of a ful l-length p-chain, but also for a V-H domain that promotes the assembly of a mu/SL chain complex.