Lethal deletion of the complement component C4 and steroid 21-hydroxylase genes in the mouse H-2 class III region, caused by meiotic recombination.

Abstract

A recombinant H-2 haplotype, designated awl8, was produced that underwent meiotic recombination in the Ea (I-E a chain)-Slp (sex-limited protein) interval of the H-2 class III region between B1O.A (H-2a) and wild-derived B1O.MOL-SGR (H-2wm7) strains. It appeared that the H-2awl8 haplotype has a single, recessive, lethal mutation, since homozygotes for H-2aw18 were not detected in progeny generated from the intercross of mice that were heterozygous for this H-2 haplotype. Nine newly established recombinant H-2 haplotypes, which arose from the heterozygous mice that resulted from a cross between common inbred H-2 haplotypes and the awl8 haplotype, allowed us to map the lethal gene to the class III region of the H-2 complex. Southern blot analysis indicated that the awl8 haplotype has a deletion of the C4 gene and a deletion of one of the steroid 21-hydroxylase genes. This result was confirmed by an immunodiffusion test that demonstrated the absence of production of the C4 protein in mice of haplotype H-2aw18. All data that were obtained supported the hypothesis that the meiotic, presumably unequal, recombination between homologous chromosomes of the H-2a and H-2wm7 haplotypes caused the deletion of the C4 and the 21-hydroxylase genes.The class III region of the mouse major histocompatibility complex (MHC), H-2, contains genes that encode components of the early portion of the complement activation pathways, such as C2, factor B (Bf), and C4 (1, 2). The Slp (sex-limited protein) gene, located in the same region, shares marked structural homology with the C4 gene, but Slp has no hemolytic activity. The biological function of Slp is still unknown. In addition to the components of the complement pathway, two structurally homologous steroid 21-hydroxylase (21-OHase) genes, 21-OHase.A and 21-OHase.B, have been mapped adjacent to the 3' ends of the Slp and the C4 genes (3). This enzyme plays a key role in the biosynthesis of adrenal steroids. A similar close linkage of the genes for C4 and 21-OHase and a duplication of a set of these two genes has been also observed in the human class III region (4). Thus, the tandem duplication of sequences spanning, at least and approximately, 55 kilobases (kb) of the DNA segment including the C4, Slp, and 21-OHase genes is a peculiar genetic configuration that is common to both the murine and the human class III region, although it is unclear whether duplication arose prior to the evolutionary differentiation of the two species or whether it arose independently after speciation (5).There are several lines of evidence that further duplication and deletion of genes in this DNA segment take place in the class III region, in both the human and the mouse. For example, Carroll et al. (6) observed human chromosomes with one, two, and three C4 loci. Furthermore, it has been reported (7, 8) that gene deletion occurs fairly frequently in human 21-OHase genes, which, in some cases, causes a congenital adrenal hyperplasia as a result of 21-OHase deficiency. Likewise, variations in the num...

Genesis by meiotic unequal crossover of a de novo deletion that contributes to steroid 21-hydroxylase deficiency.

“…Taken together, these data provide the most direct evidence yet for the natural occurrence of an unequal crossover event in mammalian genomes. In relation to these observations, an analogous meiotic recombination event has been reported in the mouse H-2 class III region, wherein indirect short-range restriction mapping and C4 allotyping analyses have suggested that the recombinant H-2awl8 haplotype differs from the parental H-2a and H-2wm7 haplotypes in lacking a C4 gene and a functional 21-OH gene (31). Although the structures of mouse C4 and 21-OH genes show close resemblances to their human homologues, the chromosomal organizations are different in that the mouse 21-OH/C4 pairs are separated by about 80 kb of DNA and it is not known whether the regular expansion/contraction events that underpin the VNTR model in humans are also applicable in mouse.…”

Restoration of adrenal steroidogenesis by adenovirus-mediated transfer of human cytochromeP450 21-hydroxylase into the adrenal gland of21-hydroxylase-deficient mice

“…4,5 A naturally occurring strain of mouse with deletion of the CYP21 and complement 4 component genes has impaired 21-OH activity and glucocorticoid production leading to hyperproduction of ACTH with adrenocortical hyperplasia and accumulation of precursor steroids. 6,7 Since the mouse adrenal lacks 17-hydroxylase, unlike the human disease, the accumulated precursor is progesterone and no androgenization occurs in this model. Also, the deletion of the gene for complement component C4 makes the 21-hydroxylase-deficient mouse different from the human disease.…”

Extra-adrenal induction of <i>Cyp21a1</i> ameliorates systemic steroid metabolism in a mouse model of congenital adrenal hyperplasia

“…First, the 21-OHD mice do not produce adrenal androgen, and therefore, they are not strictly comparable to human patients with 21-OHD [8]. Second, the present study focused only on the short term effects of Cyp21a1 induction.…”

“…Fertilized eggs of H-2 aw18 in C57BL/10SnSlc (H-2 b ) [8], a naturally occurring mouse model of 21-OHD, was kindly provided by Dr. T. Shiroishi. The eggs were transferred to a pseudo pregnant mother.…”