Genetics and expression of the Q6 and Q8 genes. An LTR-like sequence in the 3' untranslated region

Natural Loss-of-Function Mutations in Qa2 and NCF1 Cause the Spread of Mannan-Induced Psoriasis

A basis for the genetic predisposition to psoriasis is a single locus, PSORS1, within the major histocompatibility complex I region. This murine major histocompatibility complex locus encodes nonclassical molecules such as Qa2. We hypothesized that a natural loss-of-function variant of Qa2 gene clusters promotes psoriasis. In this study, we have developed a mannan-induced psoriasis model with the double deficiency of Qa2 and ROS owing to natural mutations of Qa2 gene clusters and the Ncf1 gene in the C57BL/6 background, respectively. We report three key findings in mice with mannan-induced psoriasis. A complete deficiency of Qa2 resulted in the expansion of IL-17‒producing γδ T cells and group 3 innate lymphoid cells in draining lymph nodes, leading to ear psoriasis. A single copy of Qa2-encoding genes was enough to protect against mannan-induced psoriasis, and such a protection was erased by a mutated Ncf1. Double defects with Qa2 and Ncf1 elicited a spread of exaggerated ear psoriasis to the nails, and the deficiency of γδ T cells reduced the severity of nail psoriasis. Collectively, these findings in mice provide evidence for the importance of Ncf1 mutations and Qa2 gene clusters, possibly corresponding to the PSORS1 locus in the spread of psoriasis.

MicroRNA expression in preimplantation mouse embryos from Ped gene positive compared to Ped gene negative mice

PURPOSE

The mouse preimplantation embryo development (Ped) gene product, Qa-2, influences the rate of preimplantation embryonic development and overall reproductive success. Here we investigated the expression pattern of two microRNAs, miR-125a and miR-125b, known to be involved in development in lower organisms, in preimplantation embryos from the two-cell, four-cell, eight-cell, morula, and blastocyst stages of development from the congenic B6.K1 (Ped negative) and B6.K2 (Ped positive) strains of mice.

METHOD

B6.K1 and B6.K2 congenic mice differ only in the absence (B6.K1) or presence (B6.K2) of the genes encoding Qa-2 protein. We analyzed the expression of miR-125a and miR-125b in B6.K1 and B6.K2 preimplantation embryos by using real-time PCR.

RESULT

We found no variability in miR-125b expression at any developmental stage in both strains. However, miR-125a expression increased during development in both strains and was ten times higher in Ped negative (B6.K1) embryos than in Ped positive (B6.K2) embryos by the blastocyst stage of development.

CONCLUSION

Our results show that the absence of the Ped gene profoundly affects the level of a miRNA (miR-125a) known to regulate early development. The implication is that miR-125a is likely involved in the regulation of timing of early development in mice.

Listing, location, binding motifs, and expression of nonclassical class I and related genes and molecules

The tables presented in this appendix list nonclassical class I or related genes/molecules arranged by the chromosomal region where they are encoded. This includes genes that fall into the Ib region of the murine major histocompatibility complex (MHC) which includes H2-Q, -T, and -M, as well as CD1, which lies outside the MHC region. A final table includes genes/molecules that are encoded in diverse regions. They are included in this section because they are either class I related in that their heavy chain is related to classical class I and/or they are associated with ion given is for the C57BL/6 (B6) strain unless otherwise noted.

Differential expression of Ped gene candidates in preimplantation mouse embryos

The Ped (preimplantation embryonic development) gene influences the rate of mouse preimplantation embryonic development and subsequent survival. Four similar tandem genes in the Q region of the major histocompatibility complex-Q6, Q7, Q8, and Q9-were identified as Ped gene candidates. In this study, expression of these genes during preimplantation development was examined and quantitated by reverse transcription-polymerase chain reaction and single nucleotide primer extension assays in order to investigate their contribution to the Ped gene phenotype. The Q7/Q9 gene pair was found to be transcribed in preimplantation mouse embryos, whereas transcription of the Q6/Q8 gene pair was undetectable. Both Q7 and Q9 are expressed in embryos from one Ped fast strain, C57BL/6, while only the Q9 gene is expressed in another Ped fast strain, B6.K2. These results suggest that both the Q7 and Q9 genes can function as the Ped gene in the mouse. Interestingly, the expression pattern of the Q7 and Q9 genes in preimplantation embryos is the same as in splenic lymphocytes. However, the Q6 and Q8 genes are expressed in splenic lymphocytes but not in preimplantation embryos. Treatment of mouse preimplantation embryos with interferon gamma (gamma-IFN) did not induce expression of the Q6/Q8 genes but enhanced expression of the Q7/Q9 genes. The mechanism of this differential transcription pattern is currently under investigation.

Developmental expression of the mouse MHC Q genes

To investigate the role of class Ib genes in the Q region of the mouse major histocompatibility complex (MHC), the developmental expression and foetal tissue distribution of the Q genes were studied in the C57BL/6 mouse. Using RNase protection assays, we examined Q gene expression in a wide spectrum of foetal tissues at different stages of gestation, Q4, Q6 and Q8 were widely expressed in a variety of tissues. In contrast, the expression of Q1 was restricted to the thymus and intestinal epithelium.

Autoimmunity, apoptosis defects and retroviruses

Autoimmunity and AIDS both share the common feature of increased expression of retroviral protein products and abnormal apoptosis of immune cells (81). This leads to a more global immunomodulatory defect (82-84). The challenge in the future will be to devise compounds that can either regulate the effect of the retroviral products on apoptosis, or that can inhibit apoptosis pathways in order to restore normal immune system function.

Retroviruses, apoptosis and autogenes

Autoimmunity and autoimmune disease are not the same. Autoimmunity is a normal consequence of aging, potentially reversible and possibly physiological. Autoimmune disease is dependent on genetic, viral, hormonal and psychoneuroimmunological factors. Aside from the apparently normal regulation of autoimmune responses by immune response genes, little is known about other genetic factors. Here, Norman Talal and John Mountz propose the term autogene to describe non-MHC genes which directly or indirectly interfere with important immunoregulatory actions. When mutated or otherwise genetically altered (e.g. by retrotransposon insertion), these genes predispose to immune dysregulation, lymphoproliferation and autoimmunity.

The defect in Fas mRNA expression in MRL/lpr mice is associated with insertion of the retrotransposon, ETn

Fas is a cell surface protein of the tumor necrosis factor receptor, nerve growth factor receptor, CD40 family, and is involved in the control of lymphocyte apoptosis. A mutation in the Fas gene in MRL/lpr mice results in massive lymphoproliferation (lpr) and accelerated autoimmunity. To further study the nature of this defect, Fas mRNA expression was evaluated by reverse transcriptase polymerase chain reaction as well as by Northern blotting. These studies revealed that the wild-type Fas message was produced at approximately 10-fold lower levels in the lpr compared with the ++ substrain of MRL mice. In addition to the wild-type transcript, lpr mice also synthesized chimeric transcripts containing an insertion of the early retrotransposon (ETn). Molecular cloning and nucleotide sequencing of a Fas-ETn chimeric cDNA suggested that the striking reduction in wild-type Fas mRNA levels and the presence of aberrant transcripts in MRL/lpr mice are most likely explained by the insertion of the ETn retrotransposon into an intron of the Fas gene and induction of alternative splicing involving the 5' ETn long terminal repeat.

Characterization of a class Ib gene of the rat major histocompatibility complex

The cDNA and a partial genomic sequence of a rat class I major histocompatibility (RT1) gene, 11/3R, is reported here. The sequence contains several unique amino acid residues at certain positions, mutations in exon 7 (which is not expressed), a mutation of the canonical exon 8 stop codon to a sense codon, and includes a long 3' untranslated region (utr). The structure of exon 7 differs from that found in most rat class I genes and resembles exon 7 of most H-2K,D,L,Q genes. Parts of the 3' noncoding region are homologous to the RT1.A-4 and certain H-2 genes. Expression is detectable by northern blot analysis in mitogen-stimulated lymphocytes only, by polymerase chain reaction (PCR) in each tissue tested. After transfection into L cells 11/3R can be shown to be expressible at the cell surface. Probes derived from the 3' noncoding part crosshybridize with a number of restriction fragments which map to the RT1.C region, thus defining a subfamily of RT1.C region genes. Several members of this subfamily are deleted in the lm1 RT1 mutant. The 11/3R gene presents typical features of a class Ib gene. Aspects of evolution and the potential function of the gene are discussed.

Insertional mutations in mammals and mammalian cells

The retroposon sequences, their mechanisms of transposition and the occurrence of insertional mutation in the mammalian genome are reviewed. Insertional mutations fall into two broad categories: those due to the disruption of a gene following the physical integration of a foreign DNA sequence result in loss of gene product and would be expected to be associated with a recessive mutation. A second class of insertional mutation is well documented in which upon integration the promoter/enhancer activities inherent in the retroposon genome exert their influence on neighboring genes. This promoter/enhancer activity of integrated retroposons may have effects over relatively long distances and thus limit the possibilities of establishing an association between retroposon integration and mutation. It is emphasized that a systematic search for insertional mutations in the mammalian genome involves an extensive two-dimensional array of possible retroposon sequences and mutant alleles. Present results represent only a small portion of the total array. Future studies promise to be fruitful in efforts to isolate genes through insertional tagging, to characterize the mechanisms of retroposon transposition, as well as to study the stability of the mammalian genome.

Characterization of T cell proliferative responses induced by anti-Qa-2 monoclonal antibodies

The MHC class I Qa-2 Ag are attached to the cell surface by a glycanphosphatidylinositol (GPI) anchor. Crosslinking of Qa-2 and several other cell surface Ag attached by the GPI linkage has been shown to lead to cell activation. We have developed 10 new anti-Qa-2 mAb and characterized their capacity to induce proliferation of spleen cells. In the absence of anti-Ig-mediated crosslinking, none of the mAbs alone could induce activation. However, mAb 23.1 which reacts with the alpha 3 domain of Qa-2, when combined with most of the other mAbs (alpha 1, alpha 2 domain reactive), activated cells in the absence of anti-Ig crosslinking. The mAb pair 23.1 plus 24.16 was the most proficient and induced proliferation in the absence of any exogenous second signals. Responses were greatly enhanced and equivalent to those seen with anti-CD3 by the addition of phorbol myristate acetate (PMA). Ionomycin, rIL-2, or rIL-4 also potentiated anti-Qa-2 responses but less efficiently than PMA. Significant strain variation in the magnitude Qa-2-mediated proliferative responses was observed correlating with the levels of Qa-2 expressed on the cell surface. Crosslinking of Qa-2 molecules by the mAb combinations was required because monovalent Fab fragments failed to activate cells. F(ab')2 fragments of mAb 23.1 plus 24.16 induced vigorous proliferation indicating that accessory cell presentation of the mAb via Fc receptors was not required. Immobilized (plate bound) anti-Qa-2 mAb induced proliferation suggesting that the Qa-2 pathway may be distinct from that of other GPI molecules such as Thy-1 and Ly-6. Populations enriched for T cells (approximately 95%) responded as well as whole spleen cells, whereas B lymphocytes failed to proliferate to anti-Qa-2. Both CD4+ and CD8+ cells were activated following crosslinking of Qa-2. Finally, T cell activation mediated by Qa-2 induced elevation of [Ca2+]i, IL-2R expression, and the release of IL-2. These data demonstrate that crosslinking of Qa-2 on T lymphocytes represents a potent pathway for inducing cell activation.

Isolation of virus-like (VL30) elements from the Q10 and D regions of the major histocompatibility complex

Previous studies from our laboratory have described two endogenous provirus-like sequences in a series of cosmids spanning the TL region of the major histocompatibility complex (MHC) of normal C57BL/10 mice. At least one of these viruses shares similarities with VL30 elements. To determine if additional VL30-like retroviral elements are integrated in the MHC, we constructed a cosmid library using DNA from a radiation leukemia virus (RadLV)-transformed cell line derived from C57BL/6 mice. The library was first screened using the H-2III (5') probe, which detects Class I genes of the H-2 complex. In the primary screening 163 H-2III positives were isolated. The H-2III-positive isolates were then hybridized with an AKR-derived virus probe, EcoB/S, which contains sequences from both the pol and the env genes of the virus. Nine virus-positive isolates were detected. Localization of these cosmid isolates containing viral sequences within the H-2 complex was done utilizing low-copy probes and confirmed using previously mapped cosmid isolates from other laboratories. We report here the isolation and characterization of VL30-like elements from the Qa and D regions of the MHC of several inbred mouse strains.

Biochemical differences in Qa-2 antigens expressed by Qa-2+,6+ and Qa-2+,6- strains. Evidence for differential expression of the Q7 and Q9 genes

Cell surface forms of Qa-6 class I molecules are biochemically indistinguishable from Qa-2 although Qa-6 maps telomeric to Qa-2 with the recombinant strain B6.K2. Analysis of appropriate F1 strains did not demonstrate the presence of a trans acting factor that could modify the Qa-2 molecule to produce the Qa-6 determinant. Also, neither a neighboring cell surface molecule nor oligosaccharides were found to block the recognition of the Qa-6 determinant in Qa-2+,6- strains. The 2-D gel profiles of neuraminidase or endoglycosidase treated anti-Qa-2 immunoprecipitates from lysates of cell surface iodinated Qa-2+,6+ strains revealed an additional basic polypeptide which was absent from that of Qa-2+,6- strains. Thus, differential sialylation/glycosylation of Qa-2 molecules masks detection of Qa-2 antigen heterogeneity when cell surface forms are analyzed. Qa-6+ phenotype associated polypeptides were also found at various stages of post-translational processing in cells metabolically labeled in the presence and absence of tunicamycin. Northern analyses using Q7 and Q9 specific oligonucleotide probes revealed appropriate sized transcripts for both genes in the Qa-2+,6+ strain B6 but only Q9 in the Qa-2+,6- strain B6.K2. These data demonstrate that there is structural heterogeneity in Qa-2 antigens expressed by Qa-2+,6+ and Qa-2+,6- strains which results from differential expression of the Q7 and Q9 genes.