LIMITED FUNCTIONAL DIVERSITY IN KAPPA-LIGHT-CHAINS - JUNCTIONAL SEQUENCES FROM CD43(-CELL PROGENITORS RESEMBLE THOSE FROM PERIPHERAL B-CELLS()B220(+) EARLY B)
Kd. Victor et al., LIMITED FUNCTIONAL DIVERSITY IN KAPPA-LIGHT-CHAINS - JUNCTIONAL SEQUENCES FROM CD43(-CELL PROGENITORS RESEMBLE THOSE FROM PERIPHERAL B-CELLS()B220(+) EARLY B), The Journal of immunology, 152(7), 1994, pp. 3467-3475
Among all adult T and B cell Ag receptor chains, only Ig light chains
lack N regions. It is thought that this is due to the fact that light
chain genes rearrange after heavy chain genes, and that terminal deoxy
nucleotidyl transferase, the enzyme that adds N regions, is no longer
expressed at that stage. However, this concept has been challenged rec
ently by the demonstration that 3 to 10% of B cell precursors (CD43(+)
B220(+)) appear to rearrange their light chains at approximately the s
ame time as they undergo V-H-->DJ rearrangements. To examine N region
addition in B cell precursors undergoing early kappa-chain rearrangeme
nt, we PCR amplified rearranged V(kappa)21 genes from the CD43(+)B220(
+) bone marrow cells and compared them to sequences obtained from whol
e bone marrow and spleen. Unexpectedly, all three populations showed s
imilar to 10% N region containing junctions, most consisting of only o
ne N nucleotide. Thus, even the B cell precursors that rearrange light
chains at this early stage of development lack much N region diversit
y. Twelve percent of the sequences unambiguously contained P regions,
which were from 1 to 5 nucleotides in length. All but 2 of the 41 prod
uctive rearrangements had the commonly observed CDR3 length of nine am
ino acids. Many (71%) of the sequences were out of frame. CDR3 length
was very restricted in nonproductive rearrangements too, and deletion
of nucleotides from V-kappa and J(kappa) gene segments was limited. Th
us, even at the level of nonproductive rearrangements, junctional dive
rsity is minimal for kappa-chains.