Rearrangement and expression of {chi} light chain genes can occur without {micro} heavy chain expression during differentiation of pre-B cells

The kinetics of light (L) chain gene rearrangement and expressionon mRNA and protein level has been studied with four stromalcell/IL-7 reactive, long-term in vitro proliferating pre-B celllines and clones, two from fetal liver of normal mice and twofrom fetal liver of E_µH-bcl-2 transgenic (bcl-2-tg) mice.These pre-B cell lines and clones are DJ_H-rearranged on bothH chain alleles. Two of the clones harbor H chain rearrangementswhich do not allow the expression of V_HDJ_H rearranged H chaingenes as _µH chain proteins. Upon removal of IL-7 fromthe pre-B cell cultures all four cell lines rearrange V_H-DJ_Hand V_L-J_L gene segments, loose the surface expression of c-kit,CD43, and surrogate light chain, as well as the capacity tobe clonable on stromal cells in the presence of IL-7. Pre-Bcells from normal mice die by apoptosis during differentiation,while those from bcl-2-tg mice do not. All four lines and clonesexpress comparable levels of mRNA for _µH and _µLchains with the same time kinetics during 3 days of differentiation.However, only two of the four pre-B cell lines and clones express_µH chain protein, whereas all four pre-B cell lines andclones express _µL chain protein at comparable levels between2x10⁵ and 1.40x10⁶ _µL chain molecules per cell. Theseresults suggest that _µH chain expression is not mandatoryfor rearrangement and normal expression of _µL chain geneswhen pre-B cells differentiate to B cells.