Loss of Endothelial TDP-43 Leads to Blood Brain Barrier Defects in Mouse Models of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Loss of nuclear TDP-43 occurs in a wide range of neurodegenerative diseases, and specific mutations in the TARDBP gene that encodes the protein are linked to familial Frontal Temporal Lobar Dementia (FTD), and Amyotrophic Lateral Sclerosis (ALS). Although the focus has been on neuronal cell dysfunction caused by TDP-43 variants, TARDBP mRNA transcripts are expressed at similar levels in brain endothelial cells (ECs). Since increased permeability across the blood brain barrier (BBB) precedes cognitive decline, we postulated that altered functions of TDP-43 in ECs contributes to BBB dysfunction in neurodegenerative disease. To test this hypothesis, we examined EC function and BBB properties in mice with either knock-in mutations found in ALS/FTLD patients (TARDBPG348C and GRNR493X) or EC-specific deletion of TDP-43 throughout the endothelium (Cdh5(PAC)CreERT2; Tardbpff) or restricted to brain endothelium (Slco1c1(BAC)CreERT2; Tardbpff). We found that TARDBPG348C mice exhibited increased permeability to 3kDa Texas Red dextran and NHS-biotin, relative to their littermate controls, which could be recapitulated in cultured brain ECs from these mice. Nuclear levels of TDP-43 were reduced in vitro and in vivo in ECs from TARDBPG348C mice. This coincided with a reduction in junctional proteins VE-cadherin, claudin-5 and ZO-1 in isolated ECs, supporting a cell autonomous effect on barrier function through a loss of nuclear TDP-43. We further examined two models of Tardbp deletion in ECs, and found that the loss of TDP-43 throughout the endothelium led to systemic endothelial activation and permeability. Deletion specifically within the brain endothelium acutely increased BBB permeability, and eventually led to hallmarks of FTD, including fibrin deposition, microglial and astrocyte activation, and behavioral defects. Together, these data show that TDP-43 dysfunction specifically within brain ECs would contribute to the BBB defects observed early in the progression of ALS/FTLD.

MATR3 P154S knock-in mice do not exhibit motor, muscle or neuropathologic features of ALS

Matrin 3 is a nuclear matrix protein that has many roles in RNA processing including splicing and transport of mRNA. Many missense mutations in the Matrin 3 gene (MATR3) have been linked to familial forms of amyotrophic lateral sclerosis (ALS) and distal myopathy. However, the exact role of MATR3 mutations in ALS and myopathy pathogenesis is not understood. To demonstrate a role of MATR3 mutations in vivo, we generated a novel CRISPR/Cas9 mediated knock-in mouse model harboring the MATR3 P154S mutation expressed under the control of the endogenous promoter. The P154S variant of the MATR3 gene has been linked to familial forms of ALS. Heterozygous and homozygous MATR3 P154S knock-in mice did not develop progressive motor deficits compared to wild-type mice. In addition, ALS-like pathology did not develop in nervous or muscle tissue in either heterozygous or homozygous mice. Our results suggest that the MATR3 P154S variant is not sufficient to produce ALS-like pathology in vivo.

Neurobehavioral deficits of mice expressing a low level of G127V mutant frataxin

Friedreich's ataxia (FRDA) is a neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin (FXN). Most FRDA patients are homozygous for large expansions of GAA repeats in intron 1 of FXN, while some are compound heterozygotes with an expanded GAA tract in one allele and a missense or nonsense mutation in the other. A missense mutation, changing a glycine to valine at position 130 (G130V), is prevalent among the clinical variants. We and others have demonstrated that levels of mature FXN protein in FRDA G130V samples are reduced below those detected in samples harboring homozygous repeat expansions. Little is known regarding expression and function of endogenous FXN-G130V protein due to lack of reagents and models that can distinguish the mutant FXN protein from the wild-type FXN produced from the GAA-expanded allele. We aimed to determine the effect of the G130V (murine G127V) mutation on Fxn expression and to define its multi-system impact in vivo. We used CRISPR/Cas9 to introduce the G127V missense mutation in the Fxn coding sequence and generated homozygous mice (Fxn^G127V/G127V). We also introduced the G127V mutation into a GAA repeat expansion FRDA mouse model (Fxn^GAA230/KO; KIKO) to generate a compound heterozygous strain (Fxn^G127V/GAA230). We performed neurobehavioral tests on cohorts of WT and Fxn mutant animals at three-month intervals for one year, and collected tissue samples to analyze molecular changes during that time. The endogenous Fxn G127V protein is detected at much lower levels in all tissues analyzed from Fxn^G127V/G127V mice compared to age and sex-matched WT mice without differences in Fxn transcript levels. Fxn^G127V/G127V mice are significantly smaller than WT counterparts, but perform similarly in most neurobehavioral tasks. RNA sequencing analysis revealed reduced expression of genes in oxidative phosphorylation and protein synthesis, underscoring the metabolic consequences in our mouse model expressing extremely low levels of Fxn. Results of these studies provide insight into the unique pathogenic mechanism of the FXN G130V mechanism and the tolerable limit of Fxn/FXN expression in vivo.

A Drosophila screen identifies NKCC1 as a modifier of NGLY1 deficiency

N-Glycanase 1 (NGLY1) is a cytoplasmic deglycosylating enzyme. Loss-of-function mutations in the NGLY1 gene cause NGLY1 deficiency, which is characterized by developmental delay, seizures, and a lack of sweat and tears. To model the phenotypic variability observed among patients, we crossed a Drosophila model of NGLY1 deficiency onto a panel of genetically diverse strains. The resulting progeny showed a phenotypic spectrum from 0 to 100% lethality. Association analysis on the lethality phenotype, as well as an evolutionary rate covariation analysis, generated lists of modifying genes, providing insight into NGLY1 function and disease. The top association hit was Ncc69 (human NKCC1/2), a conserved ion transporter. Analyses in NGLY1-/- mouse cells demonstrated that NKCC1 has an altered average molecular weight and reduced function. The misregulation of this ion transporter may explain the observed defects in secretory epithelium function in NGLY1 deficiency patients.

Dominant mutations of the Notch ligand Jagged1 cause peripheral neuropathy

Notch signaling is a highly conserved intercellular pathway with tightly regulated and pleiotropic roles in normal tissue development and homeostasis. Dysregulated Notch signaling has also been implicated in human disease, including multiple forms of cancer, and represents an emerging therapeutic target. Successful development of such therapeutics requires a detailed understanding of potential on-target toxicities. Here, we identify autosomal dominant mutations of the canonical Notch ligand Jagged1 (or JAG1) as a cause of peripheral nerve disease in 2 unrelated families with the hereditary axonal neuropathy Charcot-Marie-Tooth disease type 2 (CMT2). Affected individuals in both families exhibited severe vocal fold paresis, a rare feature of peripheral nerve disease that can be life-threatening. Our studies of mutant protein posttranslational modification and localization indicated that the mutations (p.Ser577Arg, p.Ser650Pro) impair protein glycosylation and reduce JAG1 cell surface expression. Mice harboring heterozygous CMT2-associated mutations exhibited mild peripheral neuropathy, and homozygous expression resulted in embryonic lethality by midgestation. Together, our findings highlight a critical role for JAG1 in maintaining peripheral nerve integrity, particularly in the recurrent laryngeal nerve, and provide a basis for the evaluation of peripheral neuropathy as part of the clinical development of Notch pathway-modulating therapeutics.

Loss of Tmem106b exacerbates FTLD pathologies and causes motor deficits in progranulin-deficient mice

Progranulin (PGRN) and transmembrane protein 106B (TMEM106B) are important lysosomal proteins implicated in frontotemporal lobar degeneration (FTLD) and other neurodegenerative disorders. Loss-of-function mutations in progranulin (GRN) are a common cause of FTLD, while TMEM106B variants have been shown to act as disease modifiers in FTLD. Overexpression of TMEM106B leads to lysosomal dysfunction, while loss of Tmem106b ameliorates lysosomal and FTLD-related pathologies in young Grn^-/- mice, suggesting that lowering TMEM106B might be an attractive strategy for therapeutic treatment of FTLD-GRN. Here, we generate and characterize older Tmem106b^-/- Grn^-/- double knockout mice, which unexpectedly show severe motor deficits and spinal cord motor neuron and myelin loss, leading to paralysis and premature death at 11-12 months. Compared to Grn^-/- , Tmem106b^-/- Grn^-/- mice have exacerbated FTLD-related pathologies, including microgliosis, astrogliosis, ubiquitin, and phospho-Tdp43 inclusions, as well as worsening of lysosomal and autophagic deficits. Our findings confirm a functional interaction between Tmem106b and Pgrn and underscore the need to rethink whether modulating TMEM106B levels is a viable therapeutic strategy.

Mitochondrial damage and senescence phenotype of cells derived from a novel frataxin G127V point mutation mouse model of Friedreich's ataxia

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin (FXN). Most FRDA patients are homozygous for large expansions of GAA repeat sequences in intron 1 of FXN, whereas a fraction of patients are compound heterozygotes, with a missense or nonsense mutation in one FXN allele and expanded GAAs in the other. A prevalent missense mutation among FRDA patients changes a glycine at position 130 to valine (G130V). Herein, we report generation of the first mouse model harboring an Fxn point mutation. Changing the evolutionarily conserved glycine 127 in mouse Fxn to valine results in a failure-to-thrive phenotype in homozygous animals and a substantially reduced number of offspring. Like G130V in FRDA, the G127V mutation results in a dramatic decrease of Fxn protein without affecting transcript synthesis or splicing. FxnG127V mouse embryonic fibroblasts exhibit significantly reduced proliferation and increased cell senescence. These defects are evident in early passage cells and are exacerbated at later passages. Furthermore, increased frequency of mitochondrial DNA lesions and fragmentation are accompanied by marked amplification of mitochondrial DNA in FxnG127V cells. Bioenergetics analyses demonstrate higher sensitivity and reduced cellular respiration of FxnG127V cells upon alteration of fatty acid availability. Importantly, substitution of FxnWT with FxnG127V is compatible with life, and cellular proliferation defects can be rescued by mitigation of oxidative stress via hypoxia or induction of the NRF2 pathway. We propose FxnG127V cells as a simple and robust model for testing therapeutic approaches for FRDA.

Strategies for assessment of botanical action on metabolic syndrome in the mouse and evidence for a genotype-specific effect of Russian tarragon in the regulation of insulin sensitivity

Published reports of botanical action are often hampered by the lack of generalized systematic approaches or by the failure to explore mechanisms that could confirm and extend the reported observations. Choice of mouse or rat housing conditions (singly or group housed) and imposed stress during handling procedures are often variable and can contribute significantly to differences in baseline phenotypes measured across studies. Differences can also be observed in the role of the extract in either the treatment of the metabolic syndrome or roles in the regulation of the emergence of metabolic syndrome. The choice of diet used can also vary between the different studies, and diet-botanical interactions must be considered. This minireview highlights the strategies being pursued by the Botanical Research Center Animal Research Core to evaluate the in vivo phenotypes of several botanical extracts during long-term feeding studies. We describe a phenotyping strategy that promotes a more rigorous interpretation of botanical action and can suggest or eliminate possible mechanisms that may be involved. We discuss the importance of selecting the mouse model, as background strain can significantly alter the underlying susceptibilities to the various components of metabolic syndrome. Finally, we present data suggesting that one of the major botanical extracts being studied, an extract of Russian tarragon, may manifest a mouse strain genotype-specific insulin-sensitizing phenotype.

Increased adiposity on normal diet, but decreased susceptibility to diet-induced obesity in mu-opioid receptor-deficient mice

The mu-opioid receptor encoded by the Oprm1 gene plays a crucial role in the mediation of food reward and drug-induced positive reinforcement, but its genetic deletion has been shown to provide food intake-independent, partial protection from diet-induced obesity. We hypothesized that mu-opioid receptor-deficient mice would show an even greater, intake-dependent, resistance to high-fat diet-induced obesity if the diet comprises a sweet component. We generated an F2 population by crossing the heterozygous offspring of homozygous female Oprm1(-/-) mice (on a mixed C57BL/6 and BALB/c genetic background) with male inbred C57BL/6 mice. Groups of genotyped wild-type (WT) and homozygous mutant (KO) males and females were fed either control chow or a high caloric palatable diet consisting of sweet, liquid chocolate-flavored Ensure together with a solid high-fat diet. Food intake, body weight, and body composition was measured over a period of 16 weeks. Unexpectedly, male, and to a lesser extent female, KO mice fed chow for the entire period showed progressively increased body weight and adiposity while eating significantly more chow. In contrast, when exposed to the sweet plus high-fat diet, male, and to a lesser extent female, KO mice gained significantly less body weight and fat mass compared to WT mice when using chow fed counterparts for reference values. Male KO mice consumed 33% less of the sweet liquid diet but increased intake of high-fat pellets, so that total calorie intake was not different from WT animals. These results demonstrate a dissociation of the role of mu-opioid receptors in the control of adiposity for different diets and sex. On a bland diet, normal receptor function appears to confer a slightly catabolic predisposition, but on a highly palatable diet, it confers an anabolic metabolic profile, favoring fat accretion. Because of the complexity of mu-opioid gene regulation and tissue distribution, more selective and targeted approaches will be necessary to fully understand the underlying mechanisms.

Effects of dietary fibers on weight gain, carbohydrate metabolism, and gastric ghrelin gene expression in mice fed a high-fat diet

Diets that are high in dietary fiber are reported to have substantial health benefits. We sought to compare the metabolic effects of 3 types of dietary fibers -- sugarcane fiber (SCF), psyllium (PSY), and cellulose (CEL) -- on body weight, carbohydrate metabolism, and stomach ghrelin gene expression in a high-fat diet-fed mouse model. Thirty-six male mice (C57BL/6) were randomly divided into 4 groups that consumed high-fat diet alone (HFD) or high-fat diet containing 10% SCF, PSY, and CEL, respectively. After baseline measurements were assessed for body weight, plasma insulin, glucose, leptin, and glucagon-like peptide 1 (GLP-1), animals were treated for 12 weeks. Parameters were reevaluated at the end of study. Whereas there was no difference at the baseline, body weight gains in the PSY and SCF groups were significantly lower than in the CEL group at the end of study. No difference in body weight was observed between the PSY and SCF animals. Body composition analysis demonstrated that fat mass in the SCF group was considerably lower than in the CEL and HFD groups. In addition, fasting plasma glucose and insulin and areas under the curve of intraperitoneal glucose tolerance test were also significantly lower in the SCF and PSY groups than in the CEL and HFD groups. Moreover, fasting plasma concentrations of leptin were significantly lower and GLP-1 level was 2-fold higher in the SCF and PSY mice than in the HFD and CEL mice. Ghrelin messenger RNA levels of stomach in the SCF group were significantly lower than in the CEL and HFD groups as well. These results suggest differences in response to dietary fiber intake in this animal model because high-fat diets incorporating dietary fibers such as SCF and PSY appeared to attenuate weight gain, enhance insulin sensitivity, and modulate leptin and GLP-1 secretion and gastric ghrelin gene expression.

The ichq mutant mouse, a model for the human skin disorder harlequin ichthyosis: mapping, keratinocyte culture, and consideration of candidate genes involved in epidermal growth regulation

Harlequin ichthyosis (HI) is a rare and usually fatal scaling skin disorder. The HI mutant mouse (ichq/ichq) has many similarities to the human disorder and provides an important model to identify candidate genes. In this study, we report refined mapping of the mouse ichq locus and consideration of the candidate genes: calpain 1 (Capn1), phospholipase C beta 3 (Plcb3), and Rela and Ikka/Chuk that encode components of the nuclear factor-kappa B (NF-kappaB) pathway. Each are strong candidates because of epidermal expression and/or changes in expression in human HI. All candidates are linked to the ichq locus on mouse Chromosome 19, although Ikka is located more distally. Genetic mapping in mouse has narrowed the ichq critical region to 4 cM. Keratinocytes from skin of +/+, +/ichq and ichq/ichq mice were cultured; all genotypes had similar expression of epidermal differentiation markers. RT-PCR amplification and sequence analysis of each candidate gene did not reveal any mutations in the ichq mouse. Mutational screening of CAPN1 cDNA from different human HI cases revealed a R433P change, but analysis of 50 normal samples demonstrated that this was an apparent polymorphism. Sequence of RELA in five unrelated human HI cases was normal. The results provide compelling evidence that none of these genes are the primary defect in the ichq mouse and that CAPN1 and RELA are not mutated in the human disorder.

Microtubule-associated protein 1A is a modifier of tubby hearing (moth1)

Once a mutation in the gene tub was identified as the cause of obesity, retinal degeneration and hearing loss in tubby mice, it became increasingly evident that the members of the tub gene family (tulps) influence maintenance and function of the neuronal cell lineage. Suggested molecular functions of tubby-like proteins include roles in vesicular trafficking, mediation of insulin signaling and gene transcription. The mechanisms through which tub functions in neurons, however, have yet to be elucidated. Here we report the positional cloning of an auditory quantitative trait locus (QTL), the modifier of tubby hearing 1 gene (moth1), whose wildtype alleles from strains AKR/J, CAST/Ei and 129P2/OlaHsd protect tubby mice from hearing loss. Through a transgenic rescue experiment, we verified that sequence polymorphisms in the neuron-specific microtubule-associated protein 1a gene (Mtap1a) observed in the susceptible strain C57BL/6J (B6) are crucial for the hearing-loss phenotype. We also show that these polymorphisms change the binding efficiency of MTAP1A to postsynaptic density molecule 95 (PSD95), a core component in the cytoarchitecture of synapses. This indicates that at least some of the observed polymorphisms are functionally important and that the hearing loss in C57BL/6J-tub/tub (B6-tub/tub) mice may be caused by impaired protein interactions involving MTAP1A. We therefore propose that tub may be associated with synaptic function in neuronal cells.

Genetic modification of hearing in tubby mice: evidence for the existence of a major gene (moth1) which protects tubby mice from hearing loss

Quantitative trait locus (QTL) analysis of genetic crosses has proven to be a useful tool for identifying loci associated with specific phenotypes and for dissecting genetic components of complex traits. Inclusion of a mutation that interacts epistatically with QTLs in genetic crosses is a unique and potentially powerful method of revealing the function of novel genes and pathways. Although we know that a mutation within the novel tub gene leads to obesity and cochlear and retinal degeneration, the biological function of the gene and the mechanism by which it induces its phenotypes are not known. In the current study, a QTL analysis for auditory brainstem response (ABR) thresholds, which indicates hearing ability, was performed in tubby mice from F(2)intercrosses between C57BL/6J- tub / tub and AKR/J-+/+ F(1)hybrids (AKR intercross) and between C57BL/6J- tub / tub and CAST/Ei.B6- tub / tub F(1)hybrids (CAST intercross). A major QTL, designated asmodifieroftubbyhearing1 ( moth1 ), was identified on chromosome 2 with a LOD score of 33.4 ( P < 10(-33)) in the AKR intercross (181 mice) and of 6.0 ( P < 10(-6)) in the CAST intercross (46 mice). This QTL is responsible for 57 and 43% of ABR threshold variance, respectively, in each strain combination. In addition, a C57BL/6J congenic line carrying a 129/Ola segment encompassing the described QTL region when made homozygous for tubby also exhibits normal hearing ability. We hypothesize that C57BL/6J carries a recessive mutation of the moth1 gene which interacts with the tub mutation to cause hearing loss in tub / tub mice. A moth1 allele from either AKR/J, CAST/Ei or 129/Ola is sufficient to protect C57BL/6J- tub / tub mice from hearing loss.

Positional cloning and molecular characterization of an immunodominant cytotoxic determinant of the mouse H3 minor histocompatibility complex

Immune responses to minor histocompatibility antigens are poorly understood and present substantial barriers to successful solid tissue and bone marrow transplantation among MHC-matched individuals. We exploited a unique positional cloning approach relying on the potent negative selection capability of cytotoxic T cells to identify the H3a gene responsible for immunodominant H2-Db-restricted determinants of the classically defined mouse autosomal H3 complex. The allelic basis for reciprocal H3a antigens is two amino acid changes within a single nonamer H2-Db-binding peptide. The H3a gene, now called Zfp106, encodes a 1888-amino acid protein with three zinc fingers and a beta-transducin domain consistent with DNA/protein binding. A region of ZFP106 is identical to a 600-amino acid sequence implicated in the insulin receptor signaling pathway.

The Molecular and Functional Characterization of a Dominant Minor H Antigen, H60

Minor histocompatibility (H) Ags elicit T cell responses and thereby cause chronic graft rejection and graft-vs-host disease among MHC identical individuals. Although numerous independent H loci exist in mice of a given MHC haplotype, certain H Ags dominate the immune response and are thus of considerable conceptual and therapeutic importance. To identify these H Ags and their genes, lacZ-inducible CD8+ T cell hybrids were generated by immunizing C57BL/6 (B6) mice with MHC identical BALB.B spleen cells. The cDNA clones encoding the precursor for the antigenic peptide/Kb MHC class I complex were isolated by expression cloning using the BCZ39.84 T cell as a probe. The cDNAs defined a new H locus (termed H60), located on mouse chromosome 10, and encoded a novel protein that contains the naturally processed octapeptide LTFNYRNL (LYL8) presented by the Kb MHC molecule. Southern blot analysis revealed that the H60 locus was polymorphic among the BALB and the B6 strains. However, none of the H60 transcripts expressed in the donor BALB spleen were detected in the host B6 strain. The expression and immunogenicity of the LYL8/Kb complex in BALB.B and CXB recombinant inbred strains strongly suggested that the H60 locus may account for one of the previously described antigenic activity among these strains. The results establish the source of an immunodominant autosomal minor H Ag that, by its differential transcription in the donor vs the host strains, provides a novel peptide/MHC target for host CD8+ T cells.

The molecular and functional characterization of a dominant minor H antigen, H60

Minor histocompatibility (H) Ags elicit T cell responses and thereby cause chronic graft rejection and graft-vs-host disease among MHC identical individuals. Although numerous independent H loci exist in mice of a given MHC haplotype, certain H Ags dominate the immune response and are thus of considerable conceptual and therapeutic importance. To identify these H Ags and their genes, lacZ-inducible CD8+ T cell hybrids were generated by immunizing C57BL/6 (B6) mice with MHC identical BALB.B spleen cells. The cDNA clones encoding the precursor for the antigenic peptide/Kb MHC class I complex were isolated by expression cloning using the BCZ39.84 T cell as a probe. The cDNAs defined a new H locus (termed H60), located on mouse chromosome 10, and encoded a novel protein that contains the naturally processed octapeptide LTFNYRNL (LYL8) presented by the Kb MHC molecule. Southern blot analysis revealed that the H60 locus was polymorphic among the BALB and the B6 strains. However, none of the H60 transcripts expressed in the donor BALB spleen were detected in the host B6 strain. The expression and immunogenicity of the LYL8/Kb complex in BALB.B and CXB recombinant inbred strains strongly suggested that the H60 locus may account for one of the previously described antigenic activity among these strains. The results establish the source of an immunodominant autosomal minor H Ag that, by its differential transcription in the donor vs the host strains, provides a novel peptide/MHC target for host CD8+ T cells.

Expression screening of a yeast artificial chromosome contig refines the location of the mouse H3a minor histocompatibility antigen gene

The H3 complex, on mouse Chromosome 2, is an important model locus for understanding mechanisms underlying non-self Ag recognition during tissue transplantation rejection between MHC-matched mouse strains. H3a is a minor histocompatibility Ag gene, located within H3, that encodes a polymorphic peptide alloantigen recognized by cytolytic T cells. Other genes within the complex include beta2-microglobulin and H3b. A yeast artificial chromosome (YAC) contig is described that spans the interval between D2Mit444 and D2Mit17, a region known to contain H3a. This contig refines the position of many genes and anonymous loci. In addition, 23 new sequence-tagged sites are described that further increase the genetic resolution surrounding H3a. A novel assay was developed to determine the location of H3a within the contig. Representative YACs were modified by retrofitting with a mammalian selectable marker, and then introduced by spheroplast fusion into mouse L cells. YAC-containing L cells were screened for the expression of the YAC-encoded H3a(a) Ag by using them as targets in a cell-mediated lympholysis assay with H3a(a)-specific CTLs. A single YAC carrying H3a was identified. Based on the location of this YAC within the contig, many candidate genes can be eliminated. The data position H3a between Tyro3 and Epb4.2, in close proximity to Capn3. These studies illustrate how genetic and genomic information can be exploited toward identifying genes encoding not only histocompatibility Ags, but also any autoantigen recognized by T cells.

Expression Screening of a Yeast Artificial Chromosome Contig Refines the Location of the Mouse H3a Minor Histocompatibility Antigen Gene

The H3 complex, on mouse Chromosome 2, is an important model locus for understanding mechanisms underlying non-self Ag recognition during tissue transplantation rejection between MHC-matched mouse strains. H3a is a minor histocompatibility Ag gene, located within H3, that encodes a polymorphic peptide alloantigen recognized by cytolytic T cells. Other genes within the complex include β2-microglobulin and H3b. A yeast artificial chromosome (YAC) contig is described that spans the interval between D2Mit444 and D2Mit17, a region known to contain H3a. This contig refines the position of many genes and anonymous loci. In addition, 23 new sequence-tagged sites are described that further increase the genetic resolution surrounding H3a. A novel assay was developed to determine the location of H3a within the contig. Representative YACs were modified by retrofitting with a mammalian selectable marker, and then introduced by spheroplast fusion into mouse L cells. YAC-containing L cells were screened for the expression of the YAC-encoded H3aa Ag by using them as targets in a cell-mediated lympholysis assay with H3aa-specific CTLs. A single YAC carrying H3a was identified. Based on the location of this YAC within the contig, many candidate genes can be eliminated. The data position H3a between Tyro3 and Epb4.2, in close proximity to Capn3. These studies illustrate how genetic and genomic information can be exploited toward identifying genes encoding not only histocompatibility Ags, but also any autoantigen recognized by T cells.

Novel HY peptide antigens presented by HLA-B27

We have identified two peptides corresponding to the male-specific HY minor histocompatibility Ags presented by HLA-B27 in transgenic rodents, isolated from whole cell extracts and from immunoprecipitated B27 molecules of male B27 rat spleen cells. HPLC peptide fractions that sensitized female B27 targets for lysis by B27-restricted anti-HY CTL were analyzed by electrospray tandem mass spectrometry using a new highly sensitive quadrupole/time-of-flight instrument. Two peptide sequences were obtained, KQYQKSTER and AVLNKSNREVR. Synthetic peptides corresponding to these sequences bound B27 in vitro and were recognized by distinct B27-restricted anti-HY CTL populations. Neither peptide sequence entirely matches known protein sequences or shows a resemblance to known Y chromosome genes, but both show homology to known autosomally encoded proteins. Both peptides were shown to be controlled by the Sxr(b) segment of the short arm of the mouse Y chromosome, a segment known to contain all previously identified HY Ags. Taken together, these findings suggest that the two peptides arise as a result of Y chromosome-regulated control of one or more autosomal gene products. Although arginine at position 2 is a dominant anchor residue for peptides bound to B27, neither B27-presented HY sequence contains this residue. These studies, employing sensitive new methodology for identification of MHC-bound peptides, significantly extend the complexity of the genetic basis of HY Ags and expand the repertoire of antigenically active peptides bound to B27.

Novel HY peptide antigens presented by HLA-B27

We have identified two peptides corresponding to the male-specific HY minor histocompatibility Ags presented by HLA-B27 in transgenic rodents, isolated from whole cell extracts and from immunoprecipitated B27 molecules of male B27 rat spleen cells. HPLC peptide fractions that sensitized female B27 targets for lysis by B27-restricted anti-HY CTL were analyzed by electrospray tandem mass spectrometry using a new highly sensitive quadrupole/time-of-flight instrument. Two peptide sequences were obtained, KQYQKSTER and AVLNKSNREVR. Synthetic peptides corresponding to these sequences bound B27 in vitro and were recognized by distinct B27-restricted anti-HY CTL populations. Neither peptide sequence entirely matches known protein sequences or shows a resemblance to known Y chromosome genes, but both show homology to known autosomally encoded proteins. Both peptides were shown to be controlled by the Sxr(b) segment of the short arm of the mouse Y chromosome, a segment known to contain all previously identified HY Ags. Taken together, these findings suggest that the two peptides arise as a result of Y chromosome-regulated control of one or more autosomal gene products. Although arginine at position 2 is a dominant anchor residue for peptides bound to B27, neither B27-presented HY sequence contains this residue. These studies, employing sensitive new methodology for identification of MHC-bound peptides, significantly extend the complexity of the genetic basis of HY Ags and expand the repertoire of antigenically active peptides bound to B27.

A genetic linkage map of mouse chromosome 2 extending from thrombospondin to paired box gene 1, including the H3 minor histocompatibility complex

The classical minor histocompatibility 3 (H3) locus was originally defined by the phenotype of skin graft rejection, which is a complex genetic trait. H3 is now known to be a gene complex comprised of a minimum of two functionally interdependent alloantigen-encoding loci, H3a and H3b. H3a encodes a peptide recognized by cytotoxic T cells, and H3b encodes a peptide that stimulates helper T cells. The H3 complex also contains the beta2-microglobulin gene (B2m), and polymorphisms in B2m contribute to the tissue rejection phenotype. We describe a high-density genetic linkage map of a 16-cM region of mouse Chromosome 2 from thrombospondin (Thbs1) to paired box gene 1 (Pax1). This genetic map includes H3a, H3b, and B2m. Other genes and anonymous loci have also been placed on the map. H3a maps between D2Mit444 and B2m in close vicinity to several known genes. H3b maps 12 cM distal to H3a, and the proprotein convertase subtilisin/kexin type 2 gene (Pcsk2; formerly Nec2) cosegregates with H3b in a high-resolution backcross panel. The H3 complex spans a region that shows conserved synteny to human chromosomes 15q, 2q, and 20p.

Gene mapping in a murine cell line by immunoselection with cytotoxic T lymphocytes

Minor histocompatibility (H) loci encode alloantigens that are recognized by cytotoxic T (Tc) lymphocytes. A (C57BL/10 x 129)F1-derived transformed lymphocyte cell line was immunoselected in vitro with cloned Tc cells that were specific for H-3aa, a Chromosome 2-encoded minor H antigen. This cell line is heterozygous at H-3a (former symbol, Cd-1) and other loci. Three groups of antigen-loss variants were identified. One group contained mutations affecting only the antigen-encoding gene. Another group probably arose through a single homologous interchromosomal exchange, resulting in extensive regions of loss of heterozygosity (LOH). The third group of variants contained an interstitial LOH, one of which was shown to be a significant deletion. Several deletion boundaries were identified, one of which ordered the closely linked H-3a and beta 2-microglobulin (B2m) genes. We suggest that Tc immunoselection against minor H antigens is a promising approach for targeting negative selection to specified chromosomal regions and can provide high-resolution genetic map information.

Bacillus subtilis flagellar proteins FliP, FliQ, FliR and FlhB are related to Shigella flexneri virulence factors

The amino acid sequences of the Bacillus subtilis flagellar proteins, FliP, FliQ, FliR and FlhB, as deduced from their respective nucleotide sequences, were found to share significant homology to the Shigella flexneri Spa24, Spa9, Spa29 and Spa40 virulence proteins, respectively. These proteins are required for the presentation of surface plasmid antigens. These results further support the growing hypothesis that a superfamily of proteins exists for the biosynthesis of supramolecular structures that lie in an external to the cell membrane.

Chemotactic methyltransferase promotes adaptation to repellents in Bacillus subtilis

Bacillus subtilis cheRB, which encodes the chemotactic methyltransferase, has been cloned and sequenced. CheRB is a polypeptide of 256 amino acids, with a predicted molecular mass of 28 kDa. A comparison of the predicted amino acid sequence of B. subtilis CheRB with that of Escherichia coli CheRE demonstrates that the two enzymes share 31% amino acid identity. The homology was functional in that the expression of cheBB in an E. coli cheRE null mutant made the bacteria Che+. In contrast to cheRE null mutants which show a strong smooth swimming bias, cheRB null mutants were predominantly tumbly. They respond to the addition and subsequent removal of attractant. They also respond to the addition of repellent but do not adapt; they resume prestimulus bias on removal of repellent. Tethering analysis of a culture of a cheRB null mutant revealed two distinct subpopulations, each demonstrating unique behaviors. One showed a strong clockwise flagellar rotation bias, whereas the other was more random. The latter phenotype may be due to a deficiency of CheB and may reflect an interaction of CheB and CheR. Measurements of CheB activity in the cheR null mutant showed them to be only 20% of wild type levels. We conclude from this work that CheRB functions to promote adaptation to repellent stimuli in B. subtilis, whereas CheRE functions to promote adaptation to attractant stimuli in E. coli.

High-resolution mapping of a minor histocompatibility antigen gene on mouse chromosome 2

Minor histocompatibility (H) loci are significant tissue transplantation barriers but are poorly understood at the genetic and molecular level. We describe the construction of a high-resolution genetic map that positions a class II MHC-restricted minor H antigen locus and orders 12 other genes and genetic markers within the we-un interval of mouse Chromosome (Chr) 2. An intersubspecific backcross between B10.UW/Sn-H-3b and CAST/Ei, an inbred stock of Mus musculus castaneus, was used for this purpose. A total of 1168 backcross mice were generated, and 71 we-un recombinants were identified. Significant compression of the genetic map in males versus females and transmission distortion of CAST-derived we, un, and Aw genes were observed. Monoclonal T cell lines specific for two minor H alloantigens, Hd-1a and Hd-2a, encoded by gene(s) that map to the we-un interval were used to antigen type the backcross mice. The results suggest the Hd-1a and Hd-2a antigens are most likely encoded by a single gene, now referred to as H-3b. The determined gene order is we-0.09 +/- 0.09-Itp-0.62 +/- 0.23-D2Mit77-0.26 +/- 0.15-[Evi-4, Pcna, Prn-p]-0.26 +/- 0.15-Scg-1-0.44 +/- 0.19-[Bmp2a, D2Mit70]-0.09 +/-. 0.09-[D2Mit19, D2Mit46]-1.59 +/- 0.36-D2Mit28-0.97 +/- 0.28-D2Ler1-1.50 +/- 0.35-H-3b-0.26 +/- 0.15-un (% recombination +/- 1 SE). Because the average resolution of the backcross is 0.09 cM, the backcross panel should facilitate the physical mapping and molecular identification of a number of genes in this chromosome region.

The genetic origin of minor histocompatibility antigens

The purpose of this study was to elucidate the genetic origin of minor histocompatibility (H) antigens. Toward this end common inbred mouse strains, distinct subspecies, and species of the subgenus Mus were examined for expression of various minor H antigens. These antigens were encoded by the classical minor H loci H-3 and H-4 or by newly identified minor H antigens detected as a consequence of mutation. Both minor H antigens that stimulate MHC class I-restricted cytotoxic T cells (Tc) and antigens that stimulate MHC class II-restricted helper T cells (Th) were monitored. The results suggested that strains of distinct ancestry commonly express identical or cross-reactive antigens. Moreover, a correlation between the lack of expression of minor H antigens and ancestral heritage was observed. To address whether the antigens found on unrelated strains were allelic with the sensitizing minor H antigens or a consequence of antigen cross-reactivity, classical genetic segregation analysis was carried out. Even in distinct subspecies and species, the minor H antigens always mapped to the site of the appropriate minor H locus. Together the results suggest: 1) minor H antigen sequences are evolutionarily stable in that their pace of antigenic change is slow enough to predate subspeciation and speciation; 2) the minor H antigens originated in the inbred strains as a consequence of a rare polymorphism or loss mutation carried in a founder mouse stock that caused the mouse to perceive the wild-type protein as foreign; 3) there is a remarkable lack of antigenic cross-reactivity between the defined minor H antigens and other gene products.

Gene-protein relationships in the flagellar hook-basal body complex of Bacillus subtilis: sequences of the flgB, flgC, flgG, fliE and fliF genes

The nucleotide sequence of five genes from the major Bacillus subtilis chemotaxis locus has been determined. Four of these genes encode proteins that are homologous to the Salmonella typhimurium FlgB, FlgC, FlgG and FliF proteins. One gene encodes a protein that is homologous to the Escherichia coli FliE protein. The data from S. typhimurium and E. coli suggest that all of these proteins form part of the hook-basal body (HBB) complex of the bacterial flagella. The FlgB, FlgC and FlgG proteins are components of the proximal and distal rods. The FliF protein forms the M-ring that anchors the rod assembly to the membrane. The role of the FliE protein within the HBB complex has not yet been determined. The similarity between the B. subtilis and S. typhimurium proteins suggests that the structure of the M-ring and the rod may be similar in the two species. However, we observed some differences in size and amino acid composition between some of the corresponding homologues that suggest the basal body proteins may be organized slightly differently within B. subtilis.

Nucleotide sequence and characterization of a Bacillus subtilis gene encoding a flagellar switch protein

The nucleotide sequence of the Bacillus subtilis fliM gene has been determined. This gene encodes a 38-kDa protein that is homologous to the FliM flagellar switch proteins of Escherichia coli and Salmonella typhimurium. Expression of this gene in Che+ cells of E. coli and B. subtilis interferes with normal chemotaxis. The nature of the chemotaxis defect is dependent upon the host used. In B. subtilis, overproduction of FliM generates mostly nonmotile cells. Those cells that are motile switch less frequently. Expression of B. subtilis FliM in E. coli also generates nonmotile cells. However, those cells that are motile have a tumble bias. The B. subtilis fliM gene cannot complement an E. coli fliM mutant. A frameshift mutation was constructed in the fliM gene, and the mutation was transferred onto the B. subtilis chromosome. The mutant has a Fla- phenotype. This phenotype is consistent with the hypothesis that the FliM protein encodes a component of the flagellar switch in B. subtilis. Additional characterization of the fliM mutant suggests that the hag and mot loci are not expressed. These loci are regulated by the SigD form of RNA polymerase. We also did not observe any methyl-accepting chemotaxis proteins in an in vivo methylation experiment. The expression of these proteins is also dependent upon SigD. It is possible that a functional basal body-hook complex may be required for the expression of SigD-regulated chemotaxis and motility genes.

Transposon Tn917lacZ mutagenesis of Bacillus subtilis: identification of two new loci required for motility and chemotaxis

We have used Tn917lacZ to mutagenize the Bacillus subtilis chromosome and have isolated mutants that are defective in chemotaxis and motility. Mapping of the transposon inserts identified two new loci. Mutations in one of these loci generated mutants that had paralyzed flagella. Accordingly, we designate this a mot locus. The other locus is closely linked to the first and encodes proteins specifying chemotaxis functions. This locus is designated the cheX locus. Both the mot and cheX loci map close to ptsI. An additional transposon insert that maps in the hag locus was obtained. The pattern of beta-galactosidase expression from some of the transposons suggested that the mot locus is regulated by sigD, a minor sigma factor of B. subtilis. The cheX locus appeared to be under the control of vegetative sigA. Four transposon inserts were mapped to a previously characterized che locus near spcB. These mutants did not produce flagellin and were defective in the methylation of the methyl-accepting chemotaxis proteins. This locus probably encodes proteins required for flagellum biosynthesis and other proteins that are required for the methylation response.

Transcriptional organization of a cloned chemotaxis locus of Bacillus subtilis

A cloned chemotaxis operon has been characterized. Thirteen representative che mutations from different complementation groups were localized on the physical map by recombination experiments. The use of integration plasmids established that at least 10 of these complementation groups within this locus are cotranscribed. An additional three complementation groups may form part of the same transcript. The direction of transcription and the time of expression were determined from chromosomal che-lacZ gene fusions. The promoter was cloned and localized to a 3-kilobase fragment. Expression of beta-galactosidase from this promoter was observed primarily during the logarithmic phase of growth. Three-factor PBS1 cotransduction experiments were performed to order the che locus with respect to adjacent markers. The cheF141 mutation is 70 to 80% linked to pyrD1. This linkage is different from that reported previously (G. W. Ordal, D. O. Nettleton, and J. A. Hoch, J. Bacteriol. 154:1088-1097, 1983). The cheM127 mutation is 57% linked by transformation to spcB3. The gene order determined from all crosses is pyrD-cheF-cheM-spcB.

A mutation in P23, the first gene in the RNA polymerase sigma A (sigma 43) operon, affects sporulation in Bacillus subtilis

Mutations within P23, the first gene of the Bacillus subtilis sigma A operon, were not detrimental to vegetative growth or sporulation. One deletion of P23 resulted in a strain that sporulated earlier than the wild type. This aberrant phenotype may be due to the simultaneous deletion of a sigma H promoter from the sigma A operon.

The nucleotide sequence and gene organization of the gerA spore germination operon of Bacillus subtilis 168

The nucleotide sequence of the second and third genes in the Bacillus subtilis spore germination locus, gerA, has been determined and the amino acid (aa) sequence was derived. Two open reading frames (ORFs), corresponding to genes II and III, encode 364-aa residue and 373-aa residue polypeptides, respectively. The gene II product, Mr 41,257, would contain long stretches of hydrophobic aa residues and may be a membrane protein; the gene III product, Mr 42,363, is relatively hydrophilic but possesses an apparent signal peptide for transfer across, and perhaps localisation on, a membrane. The ORFs for genes I and II overlap by eleven codons and the termination codon of gene II overlaps the initiation codon of gene III. Insertional inactivation experiments using integrational plasmids have indicated that the gerA locus is a single transcriptional unit. The expression of the gerA genes has been studied using a lacZ transcriptional fusion; they constitute a developmentally regulated operon.