F. Kerfourn et al., THE STRUCTURE, REARRANGEMENT AND ONTOGENIC EXPRESSION OF DB AND JB GENE SEGMENTS OF THE MEXICAN AXOLOTL T-CELL ANTIGEN RECEPTOR-BETA CHAIN (TCRB), Immunogenetics, 44(4), 1996, pp. 275-285
We sequenced a total of 189 independent rearrangements in which the VB
7.1 element is associated with CB1 (99 clones) or CB2 (90 clones) isot
ypes of the T-cell receptor (TCR) P chain in the Mexican axolotl. Thre
e stages of development were analyzed: 2.5 months, 10 months, and 25 m
onths. Three JBI segments were associated with the VB-CBI rearrangemen
ts and six JB2 segments with VB-CB2. As in other vertebrates, some ami
no acid positions were conserved in all J beta s (e.g., Phe-108, Gly-1
09, Gly-111, Thr-112, and Val-116). Two 11 nucleotides DB-like sequenc
es, differed by one (A or T) central residue and could be productively
read in the three putative reading frames. Most of the DB1 and JB1 se
gments were in the VB-CB1 clones, and most of the DB2 and JB2 segments
were in the VB-CB2 clones, suggesting that the TCRB locus is organize
d into independent DB-JB-CB clusters that used the same collection of
VB segments. About 40% of the beta-chain VDJ junctions in 2.5-month-ol
d larvae had N nucleotides, compared with about 73% in 10-25-month old
animals. The beta-chain VDJ junctions had about 30% of defective rear
rangements at all stages of development, which could be due to the slo
w rate of cell division in the axolotl lymphoid organs, and the large
genome in this urodele. Many of the axolotl CDR beta 3 sequences deduc
ed for in frame VDJ rearrangements are the same in animals of differen
t origins. Such redundancy could be a statistical effect due to the sm
all number of thymocytes in the developing axolotl, rather than to som
e bias due to junctional preferences.