REARRANGEMENT AND EXPRESSION OF KAPPA LIGHT-CHAIN GENES CAN OCCUR WITHOUT MU HEAVY-CHAIN EXPRESSION DURING DIFFERENTIATION OF PRE-B CELLS

The kinetics of kappa light (kappaL) chain gene rearrangement and expression on mRNA and protein level has been studied with four stromal cell/IL-7 reactive, long-term in vitro proliferating pre-B cell lines and clones, two from fetal liver of normal mice and two from fetal liver of EmuH-bcl-2 transgenic (bcl-2-tg) mice. These pre-B cell lines and clones are DJH-rearranged on both H chain alleles. Two of the clones harbor H chain rearrangements which do not allow the expression of V(H)DJ(H) rearranged H chain genes as muH chain proteins. Upon removal of IL-7 from the pre-B cell cultures all four cell lines rearrange V(H)-DJ(H) and V(L)-J(L) gene segments, loose the surface expression of c-kit, CD43, and surrogate light chain, as well as the capacity to be clonable on stromal cells in the presence of IL-7. Pre-B cells from normal mice die by apoptosis during differentiation, while those from bcl-2-tg mice do not. All four lines and clones express comparable levels of mRNA for muH and kappaL chains with the same time kinetics during 3 days of differentiation. However, only two of the four pre-B cell lines and clones express muH chain protein, whereas all four pre-B cell lines and clones express kappaL chain protein at comparable levels between 2 X 10(5) and 1.4 x 10(6) kappaL chain molecules per cell. These results suggest that muH chain expression is not mandatory for rearrangement and normal expression of kappaL chain genes when pre-B cells differentiate to B cells.