Genetic mapping in the major histocompatibility complex by restriction enzyme site polymorphisms: most mouse class I genes map to the Tla complex.

Abstract

From a genomic library constructed from sperm DNA of the inbred BALB/c mouse, we previously isolated 54 cosmid clones that contain 36 class I genes and can be divided by restriction map analyses into 13 gene clusters. We have isolated single-and low-copy DNA probes from each of these clusters to visualize restriction enzyme site polymorphisms in the DNAs from various congeneic and recombinant congeneic mice. These polymorphisms permit us to map each of the 13 cosmid clusters to a precise location in the major histocompatibility complex of the mouse. Thirty-one of 36 class I genes map into the TIa complex of the major histocompatibility complex whereas the remaining 5 genes map to the H-2 complex. Thus, all 36 class I genes are located in the major histocompatibility complex. Analysis of the number of restriction enzyme fragments visualized by the singleand low-copy DNA probes suggests that the class I genes in different inbred strains of mice probably undergo gene duplications and deletions, presumably by homologous but unequal crossingover.The major histocompatibility complex (MHC) of the mouse contains at least three gene families, denoted class I, class II, and class III (1-4). The molecules encoded by the class I genes fall into two categories by virtue of difference in cellular distribution, the extent of their serological polymorphisms, and their functions. The class I genes designated K, D, and L encode transplantation antigens that are found on the cell surface of most nucleated cells and are highly polymorphic (5). These integral membrane proteins serve as restricting elements that permit cytotoxic T cells to recognize viral or tumor antigens on the surface of infected or transformed cells (6). The class I genes denoted Qa-2,3, Tla, and Qa-1 encode antigens that are present on certain hematopoietic cells. They are far less polymorphic than their transplantation antigen counterparts and their functions are unknown (7).The availability of inbred strains of mice as well as congeneic mice, which are genetically identical except for the genes of the MHC, has permitted immunogeneticists to use serologic polymorphisms and recombinational analyses to identify at least six class I genes that map to two distinct complexes of MHC. The H-2 complex comprises the proximal part of the MHC on chromosome 17 and includes the K gene as its left-hand boundary and the D and L genes as its right-hand boundary. The class II and III gene families lie between the K and D regions of the H-2 complex. The Tla complex comprises the distal part of the MHC and includes the Qa-2,3, Tla, and Qa-1 genes. Various inbred strains of mice are distinguished by having different alleles at the six serologically defined loci and these constellations of alleles are denoted haplotypes. The MHC encompasses about 2 centimorgans of DNA and this may be equivalent to as much as 2,000-4,000 kilobases of DNA (1, 2, 8).We have recently isolated 54 genomic clones from a cosmid library constructed from BALB/c sperm DNA. These 54 cosmid clones cont...

A nonpolymorphic class I gene in the murine major histocompatibility complex

“…Indeed, we have noticed that the restriction map in and around a class I gene isolated from a Balb/c (H-2d haplotype) mouse library (cluster 9 in Steinmetz et al, 1982) is almost identical with the restriction map in and around the QlO gene. This gene has also been mapped to the Qa2,3 locus (Winoto et al, 1983). Thus lack of polymorphism at the QlO locus may explain why the product has not been detected serologically.…”

“…This estimate of the number of class I polypeptides contrasts with the numbers of different class i-related gene sequences that have been isolated by molecular cloning. For example, we have isolated 26 different class l-related gene sequences from a cosmid library containing C57BL/lO (H-2b) spleen DNA (Golden et al, unpublished data), and 35 gene sequences have been isolated from a Balb/c (H-2d) sperm library (Steinmetz et al, 1982;Winoto et al, 1983). The large discrepancy between the number of phenotypically characterized class I polypeptides and the number of class I gene sequences may be explained in two ways: the additional gene sequences that hybridize to the nucleic acid probes are pseudogenes-i.e., they cannot encode a class I cellsurface antigen due to a particular molecular defect; and the extra class I genes encode antigens that have not been, or cannot be, detected.…”

Molecular biology of the mouse Q region

“…The recombinants used for allocating genes to the Qa-2 region are derived from inbred mouse strains lacking the D2 and D3 genes. The probe employed by Winoto et al [8] was obtained from the D3 d gene and cross-hybridizes strongly to the 3' flanking sequence of Ql, which explains the original localization data of cluster 6. At the DNA level no linkages of genes mapping to the Q region have been reported for other mouse strains besides BIO and Balb/c.…”

Additional products of the Tla locus of the mouse.

“…For H-2, representing other class I genes, no products other than the familiar H chain were demonstrable under similar conditions. The class I members ofthe extended major histocompatibility complex of chromosome 17 of the mouse comprise a family ofgenes (H-2; Qa; Tla) that are related to one another in DNA structure (1)(2)(3)(4) and in protein-product [heavy (H)-chain] structure (5,6). The Tla gene or genes, by definition, are expressed only by thymocytes and by a proportion of T-cell leukemias presumably corresponding to the thymocyte phase of T-cell differentiation (7)(8)(9).…”