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Unequal exchange and meiotic instability of disease-resistance genes in the Rp1 region of maize.

The Rp1 region of maize was originally characterized as a complex locus which conditions resistance to the fungus Puccinia sorghi, the causal organism in the common rust disease. Some alleles of Rp1 are meiotically unstable, but the mechanism of instability is not known. We have studied the role of recombination in meiotic instability in maize lines homozygous for either Rp1-J or Rp1-G. Test cross progenies derived from a line that was homozygous for Rp1-J, but heterozygous at flanking markers, were screened for susceptible individuals. Five susceptible individuals were derived from 9772 progeny. All five had nonparental combinations of flanking markers; three had one combination of recombinant flanking markers while the other two had the opposite pair. In an identical study with Rp1-G, 20 susceptible seedlings were detected out of 5874 test cross progeny. Nineteen of these were associated with flanking marker exchange, 11 and 8 of each recombinant marker combination. Our results indicate that unequal exchange is the primary mechanism of meiotic instability of Rp1-J and Rp1-G.

Basidiomycota↗

Recombination between paralogues at the Rp1 rust resistance locus in maize.

Rp1 is a complex rust resistance locus of maize. The HRp1-D haplotype is composed of Rp1-D and eight paralogues, seven of which also code for predicted nucleotide binding site-leucine rich repeat (NBS-LRR) proteins similar to the Rp1-D gene. The paralogues are polymorphic (DNA identities 91-97%), especially in the C-terminal LRR domain. The remaining family member encodes a truncated protein that has no LRR domain. Seven of the nine family members, including the truncated gene, are transcribed. Sequence comparisons between paralogues provide evidence for past recombination events between paralogues and diversifying selection, particularly in the C-terminal half of the LRR domain. Variants selected for complete or partial loss of Rp1-D resistance can be explained by unequal crossing over that occurred mostly within coding regions. The Rp1-D gene is altered or lost in all variants, the recombination breakpoints occur throughout the genes, and most recombinant events (9/14 examined) involved the same untranscribed paralogue with the Rp1-D gene. One recombinant with a complete LRR from Rp1-D, but the amino-terminal portion from another homologue, conferred the Rp1-D specificity but with a reduced level of resistance.

Amino Acid Sequence↗

Disease expression of RP1 mutations causing autosomal dominant retinitis pigmentosa.

PURPOSE: To determine the disease expression in heterozygotes for mutations in the RP1 gene, a newly identified cause of autosomal dominant retinitis pigmentosa (adRP). METHODS: Screening strategies were used to detect disease-causing mutations in the RP1 gene, and detailed studies of phenotype were performed in a subset of the detected RP1 heterozygotes using electroretinography (ERG), psychophysics, and optical coherence tomography (OCT). RESULTS: Seventeen adRP families had heterozygous RP1 changes. Thirteen families had the Arg677ter mutation, whereas four others had one of the following: Pro658 (1-bp del), Ser747 (1-bp del), Leu762-763 (5-bp del), and Tyr1053 (1-bp del). In Arg677ter RP1 heterozygotes, there was regional retinal variation in disease, with the far peripheral inferonasal retina being most vulnerable; central and superior temporal retinal regions were better preserved. The earliest manifestation of disease was rod dysfunction, detectable as reduced rod ERG photoresponse maximum amplitude, even in heterozygotes with otherwise normal clinical, functional, and OCT cross-sectional retinal imaging results. At disease stages when cone abnormalities were present, there was greater rod than cone dysfunction. Patients with the RP1 frameshift mutations showed similarities in phenotype to those with the Arg677ter mutation. CONCLUSIONS: Earliest disease expression of RP1 gene mutations causing adRP involves primarily rod photoreceptors, and there is a gradient of vulnerability of retinopathy with more pronounced effects in the inferonasal peripheral retina. At other disease stages, cone function is also affected, and severe retina-wide degeneration can occur. The nonpenetrance or minimal disease expression in some Arg677ter mutation-positive heterozygotes suggests important roles for modifier genes or environmental factors in RP1-related disease.

Adolescent↗

Recombination at the Rp1 locus of maize.

The Rp1 locus of maize determines resistance to races of the maize rust fungus (Puccinia sorghi). Restriction fragment length polymorphism markers that closely flank Rp1 were mapped and used to study the genetic fine structure and role of recombination in the instability of this locus. Susceptible progeny, lacking the resistance of either parent, were obtained from test cross progeny of several Rp1 heterozygotes. These susceptible progeny usually had non-parental genotypes at flanking marker loci, thereby verifying their recombinational origin. Seven of eight Rp1 alleles (or genes) studied were clustered within about 0.2 map units of each other. Rp1G, however, mapped from 1-3 map units distal to other Rp1 alleles. Rp5 also mapped distally to most Rp1 alleles. Other aspects of recombination at Rp1 suggested that some alleles carry duplicated sequences, that mispairing can occur, and that unequal crossing-over may be a common phenomenon in this region; susceptible progeny from an Rp1A homozygote had recombinant flanking marker genotypes, and susceptible progeny from an Rp1D/Rp1F heterozygote showed both possible nonparental flanking marker genotypes.

Alleles↗

The properties of hybrids formed between the P-group plasmid RP1 and various plasmids from Pseudomonas aeruginosa.

R38, R931-1, and R933 are conjugative plasmids derived from strains of Pseudomonas aeruginosa. They confer resistance to mercuric ions (Hg-r), and do not tranfer from P. aeruginosa to Escherichia coli at detectable frequencies. Hybrids between each of these plasmids and the P-group plasmid, RP1, have been detected among the rare Hg-r transconjugants arising from matings of P. aeruginosa PAO donors (RP1 + R+) and E. coli K12 recipients. Two independently isolated hybrid plasmids from each of the three mating combinations have been studied. All were found to confer the entire marker phenotype of RP1, but only the Hg-r phenotype of their second parent. Moreover, all were larger than RP1 but comprised only two groups of sizes; those increased by about 14 x 10(6) daltons (the RP1/R38 hybrids), and those increased by about 30 x 10(6) daltons (the RP1/R931-1 and RP1/R933 hybrids). The hybrid plasmids were all too large to be transduced intact by phage F116L, but tranduction of fragments was possible. Thus, the determinants for both carbenicillin-resistance (Cb-r) (from RP1) and mercuric-ion-resistance could be "rescued" by recipients that already carried an RP1-like plasmid and were recombination-proficient. A molecular analysis of the plasmids recovered from such transductants suggested that each of the parental hybrids was comprised of an entire RP1 genome into which a fragment of heterologous DNA had been inserted. In similar experiments in which the recipient carried a derivative of R931-1, the Hg-r but not the Cb-r determinant could be rescued. This suggested that R38, R931-1, and R933 shared sufficient homology in the region of the mer gene for recombination to occur between them. The reason for the inability to rescue the Cb-r determinant was also investigated.

Chromosome Mapping↗

Downregulation of the potential suppressor gene IGFBP-rP1 in human breast cancer is associated with inactivation of the retinoblastoma protein, cyclin E overexpression and increased proliferation in estrogen receptor negative tumors.

The complex insulin-like growth factor network of ligands, receptors and binding proteins has been shown to be disturbed in breast cancer. In addition to defects in proteins controlling cell cycle checkpoints, this type of aberrations could affect tumor growth and survival thereby influencing both tumor aggressiveness and potential response to treatments. We have previously identified the T1A12/mac25 protein, which is identical to the IGFBP-rP1, as a differentially expressed gene product in breast cancer cells compared with normal cells. Here we compare the expression of IGFBP-rP1 in 106 tumor samples with known status of cell cycle aberrations and other clinicopathological data. This was done using a tumor tissue section array system that allows for simultaneous immunohistochemical staining of all samples in parallel. Cytoplasmic staining of variable intensity was observed in most tumors, 15% lacked IGFBP-rP1 staining completely, 20% had weak staining, 32% intermediate and 33% showed strong staining. Low IGFBP-rP1 was associated with high cyclin E protein content, retinoblastoma protein (pRb) inactivation, low bcl-2 protein, poorly differentiated tumors and higher stage. There was a significantly impaired prognosis for patients with low IGFBP-rP1 protein tumors. Interestingly, IGFBP-rP1 showed an inverse association with proliferation (Ki-67%) in estrogen receptor negative tumors as well as in cyclin E high tumors suggesting a separate cell cycle regulatory function for IGFBP-rP1 independent of interaction with the estrogen receptor or the pRb pathway.

Aneuploidy↗

Mutations in the RP1 gene causing autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration that affects approximately 1 in 3500 people worldwide. Recently we identified the gene responsible for the RP1 form of autosomal dominant retinitis pigmentosa (adRP) at 8q11-12 and found two different nonsense mutations in three families previously mapped to 8q. The RP1 gene is an unusually large protein, 2156 amino acids in length, but is comprised of four exons only. To determine the frequency and range of mutations in RP1 we screened probands from 56 large adRP families for mutations in the entire gene. After preliminary results indicated that mutations seem to cluster in a 442 nucleotide segment of exon 4, an additional 194 probands with adRP and 409 probands with other degenerative retinal diseases were tested for mutations in this region alone. We identified eight different disease-causing mutations in 17 of the 250 adRP probands tested. All of these mutations are either nonsense or frameshift mutations and lead to a severely truncated protein. Two of the eight different mutations, Arg677X and a 5 bp deletion of nucleotides 2280-2284, were reported previously, while the remaining six mutations are novel. We also identified two rare missense changes in two other families, one new polymorphic amino acid substitution, one silent substitution and a rare variant in the 5'-untranslated region that is not associated with disease. Based on this study, mutations in RP1 appear to cause at least 7% (17/250) of adRP. The 5 bp deletion of nucleotides 2280-2284 and the Arg677X nonsense mutation account for 59% (10/17) of these mutations. Further studies will determine whether missense changes in the RP1 gene are associated with disease, whether mutations in other regions of RP1 can cause forms of retinal disease other than adRP and whether the background variation in either the mutated or wild-type RP1 allele plays a role in the disease phenotype.

Adult↗

Comparative sequence analysis of the sorghum Rph region and the maize Rp1 resistance gene complex.

A 268-kb chromosomal segment containing sorghum (Sorghum bicolor) genes that are orthologous to the maize (Zea mays) Rp1 disease resistance (R) gene complex was sequenced. A region of approximately 27 kb in sorghum was found to contain five Rp1 homologs, but most have structures indicating that they are not functional. In contrast, maize inbred B73 has 15 Rp1 homologs in two nearby clusters of 250 and 300 kb. As at maize Rp1, the cluster of R gene homologs is interrupted by the presence of several genes that appear to have no resistance role, but these genes were different from the ones found within the maize Rp1 complex. More than 200 kb of DNA downstream from the sorghum Rp1-orthologous R gene cluster was sequenced and found to contain many duplicated and/or truncated genes. None of the duplications currently exist as simple tandem events, suggesting that numerous rearrangements were required to generate the current genomic structure. Four truncated genes were observed, including one gene that appears to have both 5' and 3' deletions. The maize Rp1 region is also unusually enriched in truncated genes. Hence, the orthologous maize and sorghum regions share numerous structural features, but all involve events that occurred independently in each species. The data suggest that complex R gene clusters are unusually prone to frequent internal and adjacent chromosomal rearrangements of several types.

Carrier Proteins↗

Structural analysis of the maize rp1 complex reveals numerous sites and unexpected mechanisms of local rearrangement.

Rp1 is a complex disease resistance locus in maize that is exceptional in both allelic variability and meiotic instability. Genomic sequence analysis of three maize BACs from the Rp1 region of the B73 inbred line revealed 4 Rp1 homologs and 18 other gene-homologous sequences, of which at least 16 are truncated. Thirteen of the truncated genes are found in three clusters, suggesting that they arose from multiple illegitimate break repairs at the same sites or from complex repairs of each of these sites with multiple unlinked DNA templates. A 43-kb region that contains an Rp1 homolog, six truncated genes, and three Opie retrotransposons was found to be duplicated in this region. This duplication is relatively recent, occurring after the insertion of the three Opie elements. The breakpoints of the duplication are outside of any genes or identified repeat sequence, suggesting a duplication mechanism that did not involve unequal recombination. A physical map and partial sequencing of the Rp1 complex indicate the presence of 15 Rp1 homologs in regions of approximately 250 and 300 kb in the B73 inbred line. Comparison of fully sequenced Rp1-homologous sequences in the region demonstrates a history of unequal recombination and diversifying selection within the Leu-rich repeat 2 region, resulting in chimeric gene structures.

Chromosome Mapping↗

De novo mutation in the RP1 gene (Arg677ter) associated with retinitis pigmentosa.

PURPOSE: The Arg677ter mutation in the RP1 gene is one of the most common causes of autosomal dominant retinitis pigmentosa (RP). In the current study, a de novo Arg677ter RP1 gene mutation was identified in a patient with RP. METHODS: RP1 gene mutation screening was performed in probands with simplex RP. In one proband with the RP1 mutation, paternity was established by analyzing 24 short tandem repeat polymorphisms. Additional candidate RP genes, including rhodopsin, RDS/peripherin, RP2, and RPGR, were also examined in this proband. Phenotype was characterized with psychophysics, electroretinography, and optical coherence tomography. RESULTS: An RP1 (Arg677ter) mutation was identified in one of the patients with simplex RP, but the sequence change was not detected in his parents. Parentage was confirmed, and other candidate genes were negative for mutations. Retinal function and cross-sectional imaging studies in the patient indicated greater rod than cone dysfunction with a photoreceptor basis for the abnormalities. CONCLUSIONS: The de novo origin of an RP1 (Arg677ter) mutation in a patient with simplex RP suggests that this common autosomal dominant RP mutation can arise independently in the population and supports the hypothesis of a mutational hotspot in the RP1 gene.

Adult↗

Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) is a potential tumor suppressor protein for prostate cancer.

Insulin-like growth factor binding protein-related protein-1 (IGFBP-rP1) has been shown to have decreased expression in the progression from benign to malignant prostate epithelial cells (V. Hwa et al., J. Clin Endocrinol. Metab., 83: 4355-4362, 1998). The present study was undertaken to determine the effects of the re-expression of IGFBP-rP1 in a cell line from a model of human prostate cancer, M12, in which IGFBP-rP1 expression had been demonstrated to decrease from the parent epithelial cell, P69, to the malignant subline, M12. An IGFBP-rP1 cDNA encoding the protein was transfected into M12 cells in a plasmid that resulted in constitutive-expression of IGFBP-rP1. Clones of transfected M12 cells were selected for low (L) and high (H) levels of expression, and the plasmid vector alone was transfected into M12 as a control. After transfection, there was a marked alteration in the morphology of the M12 cells such that the H clones had an elongated appearance when compared with the M12 control cells. The M12 clones overexpressing IGFBP-rP1 had a dose-related increase in population doubling time, decreased colony formation in soft agar, an increased propensity to undergo apoptosis in response to 6-hydroxyurea, and decreased tumor formation in male athymic, nude mice. These data suggest that IGFBP-rP1 may have a suppressive effect on prostate cancer development.

Animals↗

Human prostate cancer expresses the low affinity insulin-like growth factor binding protein IGFBP-rP1.

Many of the alterations in the insulin-like growth factor (IGF) axis in prostatic disease have been associated with changes in the insulin-like growth factor binding proteins (IGFBPs), a multigene family of proteins that are thought to mediate the action of IGFs on target tissues. IGFBP-related protein 1 (rP1), also known as IGFBP-7 or mac25, is a recently described member of the IGFBP family, the biological function of which has yet to be completely ascertained. In this study, we analyzed the localization of IGFBP-rP1 in prostate cancer and benign prostate tissues using immunohistochemistry and a polyclonal antibody, T1A12, that is specific for IGFBP-rP1. The most intense staining was observed in nerves, whereas smooth muscle cells in the prostate stained weakly. Lymphocytes were always negative. When normal prostatic secretory epithelium was present, staining was usually absent. The lining secretory epithelium stained positively in 0 of 12 (0%) cases of benign prostatic hyperplasia, 57 of 63 (90.5%) primary adenocarcinomas, and 7 of 7 (100%) prostate cancer metastases. Prostatic intraepithelial neoplasia showed a similar pattern of staining to that observed for the invasive tumors. Analysis of Northern blots showed that none of the prostate cancer cell lines (LNCaP, C4, C4-2, C4-2B4, 9069E3, DU145, and PC3) expressed IGFBP-rP1 mRNA. This lack of expression was confirmed by immunohistochemistry of s.c.-generated tumor xenografts of LNCaP and C4-2 and by immunoblot on serum-free-conditioned media from all prostatic cell lines. In contrast to these results, tumor xenografts generated by direct intraosseous injection of LNCaP or C4-2 to bone marrow space resulted in tumors that stained positively for IGFBP-rP1. Our results show that IGFBP-rP1 is expressed in both in situ and invasive prostate neoplasms, but not typically in normal secretory or BPH epithelium; furthermore, the expression of IGFBP-rP1 can be induced in human prostate cancer cell lines in vivo on interaction with an appropriate host environment.

Carrier Proteins↗

[Digenic association of RHO and RP1 genes with retinitis pigmentosa among Chinese population in Hong Kong].

OBJECTIVE: To identify the mutation patterns of RHO and RP1 genes in the Chinese patients with retinitis pigmentosa (RP) and to explore their potential interactions in the pathogenesis of RP. METHODS: Sequence alterations in the entire coding region and splice sites of RHO and RP1 gene were screened in 151 RP affected probands and 150 unrelated controls who were all Hong Kong Chinese. Additional 46 relatives of 12 RP probands carrying possible mutations in RHO or RP1 were recruited for segregation analysis. Univariate analysis, multivariate analysis and genotype-pedigree disequilibrium test were used to examine the associations of polymorphisms in these two genes with RP. RESULTS: Two mutations in the RHO gene, 5211delC and P347L, were identified each in one proband from the 151 probands, accounting for 1.3% of the RP patients. Two mutations in the RP1 gene, R677X and D984G, were identified each in one proband from the 151 probands, also accounting for 1.3% of the RP patients. In univariate analysis, non-coding sequence variants in the RHO gene, -26G > A, was found to increase the risk of RP, while R872H in the RP1 gene was likely to be a protective factor for RP. Multivariable logistic regression analysis and haplotype analysis confirmed these associations. CONCLUSION: The prevalences of RHO and RP1 mutations among the RP patients in Chinese population are both less than reported in other populations. Besides the disease-causing mutations, non-coding sequence alterations may also be a modifier for RP. The potential interactions between RHO and RP1 suggest a digenic etiology for RP.

Adolescent↗

Evaluation of chemopreventive action of Ginsenoside Rp1.

We evaluated the chemopreventive properties of Ginsenoside Rp1 on 7,12-Dimethyl benz (a) anthracene (DMBA) skin papillomagenesis in Swiss albino mice. A significant reduction in values of tumor incidence, tumor burden, and cumulative number of papilloma was observed in mice treated orally with Ginsenoside Rp1 continuously at pre-, peri- and post-initiational stages of papillomagenesis as compared to the control group. Chemopreventive potential of Ginsenoside Rp1 was also observed on the skin metabolizing enzymes in Swiss albino mice. Ginsenoside Rp1 produced a significant elevation in the skin microsomal cytochrome p-450 and cytochrome b5, glutathione S-transferase (GST), reduced glutathione (GSH), glutathione peroxidase (GPX), glutathione reductase (GR), DT-diaphorase, superoxide dismutase (SOD) and catalase levels in the group of mice treated with Ginsenoside Rp1 for seven consecutive days. However, there was significant decrease in lipid peroxidation (LPO) level in Ginsenoside Rp1 treated group.

9,10-Dimethyl-1,2-benzanthracene↗

Recombination events generating a novel Rp1 race specificity.

Genes at the maize Rp1 rust resistance complex often mispair in meiosis, which allows genes to recombine unequally, creating recombinant haplotypes. Four recombinant haplotypes were identified from progeny of an Rp1-D/Rp1-I heterozygote that conferred a nonparental resistance specificity designated Rp1-I*. Sequence comparisons of paralogs in the recombinant and parental haplotypes demonstrated that all four recombinants were derived from intergenic (between gene) recombination events. The sequence of paralogs in the HRp1-I parental haplotype indicated this haplotype includes 41 or more rp1 genes, at least 31 of which are transcribed. The results indicate that most of the novel resistance specificities that have arisen spontaneously at Rp1 are the result of reassort ment of existing Rp1 genes.

Base Sequence↗

Transposition of a beta-lactamase locus from RP1 into Pseudomonas putida degradative plasmids.

The beta-lactamase gene from the RP1 plasmid transposes into at least two Pseudomonas putida degradative plasmids. Donor strains that carry RP1 (bla+ tet+ aphA+) and a degradative plasmid yield transconjugants that have only the bla+ marker of RP1. This occurs in up to 80% of all bla+ transconjugants. Segregation of the bla+ marker requires the presence of a degradative plasmid in the donor and is only observed in transconjugants that have received degradative markers. The bla+ tet aphA transconjugants show 100% linkage of bla+ to degradative markers in conjugation,transduction, and transformation crosses. A transduction cross of an (RP1), (SAL) donor shows that 8% of all SAL plasmids also carry the transposed bla+ marker. Tn401 is the name we assign to the bla+ transposon from RP1 observed in Pseudomonas. Its identity with the RP1 bla+ transposon observed in Escherichia coli is not known. In four cases, Tn401 has inserted into the camphor genes of the CAM-OCT plasmid.

Alkanes↗

A novel mutation of the RP1 gene (Lys778ter) associated with autosomal dominant retinitis pigmentosa.

BACKGROUND: Besides the three known genes (RHO, RDS/Peripherin, NRL) involved in autosomal dominant retinitis pigmentosa (adRP), a fourth gene, RP1, has been recently identified. Initial reports suggest that mutations in the RP1 gene are the second most frequent cause of adRP. The clinical findings were described in a family with adRP and a novel mutation in the RP1 gene. METHOD: Index patients from 15 independent families with adRP in which RHO mutations had been excluded in previous examinations were screened for mutations in the RP1 gene by means of direct DNA sequencing. Evaluation of the RP1 phenotype in patients included funduscopy, kinetic perimetry, dark adapted final threshold test, standard electroretinography and, in one case, multifocal electroretinography. RESULTS: One novel nonsense mutation (Lys778ter) in one of these 15 patients was detected. Cosegregation of the mutation with the disease phenotype could be established in the index patient's family. The phenotype comprises variable expression of clinical disease probably including one case of incomplete penetrance, a onset of symptoms beginning in adulthood, and evidence of regionally varying retinal function loss. CONCLUSION: The Lys778ter mutation localises inside the critical region harbouring all mutations described so far. The ophthalmic findings support previous observations that variation of disease expression appears as a typical feature of the RP1 phenotype.

Aged↗

Autosomal recessive retinitis pigmentosa is associated with mutations in RP1 in three consanguineous Pakistani families.

PURPOSE: To localize and identify the gene and mutations causing autosomal recessive retinitis pigmentosa in three consanguineous Pakistani families. METHODS: Blood samples were collected and DNA was extracted. A genome-wide scan was performed by using 382 polymorphic microsatellite markers on genomic DNA from affected and unaffected family members, and lod scores were calculated. RESULTS: A genome-wide scan of 25 families gave an hlod = 4.53 with D8S260. Retinitis pigmentosa in all three families mapped to a 14.21-cM (21.19-Mb) region on chromosome 8 at q11, flanked by D8S532 and D8S260. This region harbors RP1, which is known to cause autosomal dominant retinitis pigmentosa. Sequencing of the coding exons of RP1 showed mutations in all three families: two single-base deletions, c.4703delA and c.5400delA, resulting in a frame shift, and a 4-bp insertion, c.1606insTGAA, all causing premature termination of the protein. All affected individuals in these families are homozygous for the mutations. Parents and siblings heterozygous for the mutant allele did not show any signs or symptoms of RP. CONCLUSIONS: These results provide strong evidence that mutations in RP1 can result in recessive as well as dominant retinitis pigmentosa. The findings suggest that truncation of RP1 before the BIF motif or within the terminal portion results in a simple loss of RP1 function, producing a recessive inheritance pattern. In contrast, disruption of RP1 within or immediately after the BIF domain may result in a protein with a deleterious effect and hence a dominant inheritance pattern.

Chromosomes, Human, Pair 8↗