Mouse Immunoglobulin Heavy Chain Gene Research Articles

Identification of D segments of immunoglobulin heavy-chain genes and their rearrangement in T lymphocytes.

The finding that the diversity (D) and joining (JH) but not the variable (VH) DNA segments of mouse immunoglobulin heavy-chain genes are joined in the DNA of some cloned cytolytic T cells, led to identification and sequencing of three different D DNA segments. Two segments identified on the embryo DNA carry on both the 5' and 3' sides two sets of characteristic sequences separated by a 12-base pair spacer, which have been implicated as recognition signals for a recombinase. The third segment, identified in a form joined with a JHDNA segment in a T cell, carries the recognition signal on the 5' side. These results support the 12/23-base pair model for somatic generation of immunoglobulin V genes, and rule out the possibility that the cytolytic T cells use assembled VH, D and JH sequences to encode their antigen receptors.

Ordering of mouse immunoglobulin heavy chain genes by molecular cloning.

We have determined the order of the mouse immunoglobulin gamma 1, gamma 2 b, gamma 2 a and epsilon genes by molecular cloning of overlapping chromosomal segments. The results clearly demonstrate that the order is 5'-gamma 1-(21 kilobases)-gamma 2b-(15 kilobases)-gamma 2a-(15 kilobases)-epsilon-3'. There seem to be no J regions at the 5' side of each constant region gene so far obtained except for the mu gene and these constant region genes seem to have repetitive sequences characteristic of switch (S) regions at their 5' side.

Deletions are associated with somatic rearrangement of immunoglobulin heavy chain genes

The organization of mouse immunoglobulin heavy chain genes has been investigated by hybridization with cloned μ and α cDNA probes. Restriction endonuclease fragments bearing μ and α constant region genes and two types of variable region (V H) genes were compared in BALB/c embryos, liver and nine plasmacytomas synthesizing IgM, IgA, IgG 1, IgG 2a, IgG 2b and IgG 3. Embryo DNA was found to contain a single copy of the C μ gene per haploid genome. In contrast, one V H probe (HPC 76) detected at least six related V H genes, while the other (S107) detected a separate set of at least four genes, indicating that the germline contains distinct sets of multiple related V H genes. Most V H genes within the two subsets remained in germline context in different plasmacytomas, providing no evidence for somatic reassortment of V H genes. One plasmacytoma was devoid of specific V H genes, including some related to the expressed V H sequence. This may mean that the translocation event creating an active heavy chain gene involves deletion of the DNA between the expressed V H and C H sequences. The context of C H sequences in DNA from a plasmacytoma secreting IgM differed from that in embryo DNA, as did C α sequences in two IgA- and several IgG-secreting plasmacytomas. Unlike heavy chain expression, rearrangement was not confined to one allele and often took different forms within a single cell line, presumably varying on different homologous chromosomes. Each rearrangement, whether resulting in an active C gene or not, appeared to change sequences upstream but not downstream from the C H gene. Significantly, the eight IgG and IgA plasmacytomas examined had undergone deletions of at least half and often all C μ sequences while retaining the embryo level of C α sequences. Hence a deletion mechanism may be responsible for the switch in expression from one C H gene to another which occurs during differentiation of a lymphocyte clone.

Mutual homology of mouse immunoglobulin gamma-chain gene sequences.

We have assessed the relative homology of mouse immunoglobulin heavy-chain gene sequence using complementary DNAs (cDNAs) synthesized against gamma-chain mRNAs (gamma 1, gamma 2a, gamma 2b, and gamma 3) purified from mouse myelomas. cDNAs complementary to the gamma-chain mRNAs did not cross-hybridize with the mu- and alpha-chain mRNAs, whereas they cross-hybridized to significant extents (22--66%) with the gamma-chain mRNAs of other subclasses. The heterologous hybrids formed, however, melt at 5--13 degrees C lower temperatures as compared to the homologous hybrids, indicating that significant portions of the heterologous hybrids are mismatched. The rates of the cross-hybridization reactions are 2- to 17-fold slower than those of the homologous hybridization reactions. Therefore, the gamma-chain gene sequences of four subclasses share a part of homology with each other, but they are different enough to be measured separately. Cross-hybridization analysis indicate that the gamma 2a and gamma 2b genes are the most closely related, while the gamma 1 and gamma 3 genes are the least related among the gamma subclass genes.