Immunoglobulin λ Gene Rearrangement Can Precede κ Gene Rearrangement
Immunoglobulin Gene Rearrangement Can Precede Gene Rearrangement
JORG BERG 0
MINDY MCDOWELL 0
HANS-MARTIN JCK 0
MATTHIAS WABL 0
0 Department of Microbiology and Immulology, University of California , San Francisco, California 94143-0414 , USA
Immunoglobulin genes are generated during differentiation of B lymphocytes by joining but no light-chain.gene. Although there is only one heavy-chain locus, there are two lightgene segments. A mouse pre-B cell contains a functional immunoglobulin heavy-chain gene, chain loci: c and It has been reported that c loci in the germ-line configuration are never (in man) or very rarely (in the mouse) present in cells with functionally rearranged -chain genes. Two explanations have been proposed to explain this: (a) the ordered rearrangement theory, which postulates that light-chain gene rearrangement in the pre-B cell is first attempted at the c locus, and that only upon failure to produce a functional n: chain is there an attempt to rearran,ge the ;t locus; and (b) the stochastic theory, which postulates that rearrangement at the locus proceeds at a rate that is intrinsically much slower than that at the c locus. We show here that ;-chain genes are generated whether or not the c locus has lost its germ-line arrangement, a result that is compatible only with the stochastic theory.
Isotypic exclusion; n; germ-line arrangement; stochastic theory; ordered rearrangement theory
INTRODUCTION
Immunoglobulins consist of two identical heavy (H)
chains and two identical light (L) chains. Both H
and L chains consist of variable (V) and constant (C)
regions. A given lymphocyte produces only one type
of V region pair, i.e., it is monospecific. Although B
lymphocytes are diploid, the products of only one
allele encoding H, and one allele encoding L, are
expressed on the cell membrane. This phenomenon,
called allelic exclusion, is necessary to ensure the
monospecificity of B lymphocytes
(Pernis et al.,
1965; Weiler, 1965)
. At tle L-chain loci,
monospecificity requires isotypic exclusion in addition to
allelic exclusion. That is, a B cell expresses either n:
VX2
*Corresponding author.
or
but not both. In the mouse, the one VI gene
segment (see Fig. 1) can combine with either the
joining (J) ,1 or J,3 segment to form a ;1 or
gene with the nearest C segment, and the one V,2
gene segment can join either to J,2 to form a ,2
gene or to J,l or J3 to form the rare genes that
contain V2 and C,1, or V,2 and C3
(Blomberg et
al., 1981; Reilly et al., 1984; Weiss et al., 1985)
.
Isotypic exclusion extencls also to these various genes
within the
locus.
In mouse c-producing cells, the
but most of the
rearranged,
examined so far contained no n: loci in the germ-line
locus is rarely
X-producing cells
configuration; only one c locus in the germ-line
configuration was detected in 11 -producing
hybridomas
(Coleclough.et al., 1981)
. In the mouse,
there are over 200 Vc genes, but only two V, genes.
It was argued that the enzyme(s) joining the V gene
segment to the J gene segment will have a greater
chance of binding to a recognition sequence
belonging to a Vc than to a V, gene, and that the
asymmetry in the behavior of the two L-chain loci
could be explained by a simple stochastic model
with unequal rate constants
(Coleclough et al.,
1981)
. The n::, ratio of 95:5 in mouse serum is
consistent with this view. However, in human
serum, the n::, ratio is 60:40, and in the human
producing B cells examined so far, there were no
loci in the .germ-line configuration
(Hieter et al.,
1981)
. And, except for one case
(Denny et al., 1985)
,
there were no rearrangements in human
cproducing cells
(Hieter et al., 1981)
. This led to the
idea, now widely accepted, that n: rearrangement
obligatorily precedes rearrangement, and that
rearrangement will be attempted only if c
rearrangement fails to produce a functional c gene
(Hieter et al., 1981; Alt et al., 1986)
. On this theory,
isotypic exclusion has a different basis than allelic
exclusion.
To get a better understanding of what is
happening at the L loci, it is important to consider
the effect of c deletion. In the mouse, of the 22
alleles in 11 ,-producing hybridomas investigated so
far, 14 were nonproductively rearranged, 1 was in
the germ-line configuration, and 7 were deleted
(Coleclough et al., 1981)
. In human ,-producing
cells, 1 of 20 c alleles was nonproductively
rearranged, and 19 were deleted
(Hieter et al., 1981)
.
Thus, it is possible that the c alleles are deleted after
gene rearrangement, and that, therefore, the
stochastic theory may have been prematurely
dismissed.
o cN
K probe
(A)
kb
RESULTS AND DISCUSSION
n: Germ-Line Arrangement in a ;L-Producing
Myeloma
The first clue that the alleles are deleted after
gene rearrangement came from our investigation of FIGURE 2. Southern blot analysis of HindllI-digested DNA from
the ,-producing mouse myeloma J558, which has various mouse cell lines. The hybridizing c probe is a Hindlll
b (...truncated)