Search PubMed⌕ Search

Biomedical subjects

R J Scott

Publications and source records attributed to R J Scott.

At least 73 records · Page 4Linked to original sources
PubMed1998

Parent-of-origin effects on seed development in Arabidopsis thaliana.

Many flowering plants are polyploid, but crosses between individuals of different ploidies produce seeds that develop abnormally and usually abort. Often, seeds from interploidy crosses develop differently depending on whether the mother or father contributes more chromosome sets, suggesting that maternal and paternal genomes are not functionally equivalent. Here we present the first cytological investigation of seed development following interploidy crosses in Arabidopsis thaliana. We find that crosses between diploid and tetraploid plants in either direction, resulting in double the normal dose of maternal or paternal genomes in the seed, produce viable seeds containing triploid embryos. However, development of the seed and in particular the endosperm is abnormal, with maternal and paternal genomic excess producing complementary phenotypes. A double dose of maternal genomes with respect to paternal contribution inhibits endosperm development and ultimately produces a smaller embryo. In contrast, a double dose of paternal genomes promotes growth of the endosperm and embryo. Reciprocal crosses between diploids and hexaploids, resulting in a triple dose of maternal or paternal genomes, produce seeds that begin development with similar but more extreme phenotypes than those with a double dose, but these invariably abort. One explanation of our observations is that seeds with maternal or paternal excess contain different doses of maternally or paternally expressed imprinted loci affecting endosperm development.

Arabidopsis↗
PubMed1997

New deletion in low-grade oligodendroglioma at the glioblastoma suppressor locus on chromosome 10q25-26.

Loss of heterozygosity on chromosome 10 is considered to be associated with the progression of glioblastomas. Two closely related regions have recently been proposed to contain the glioblastoma suppressor locus on chromosome 10q25-26; a 1 cM region between the polymorphic (CA)n-repeat markers D10S587 and D10S216, and an area of 5 cM between the markers D10S221 and D10S209. To confirm and further delineate this region, we analyzed 51 glioblastomas and 11 intermediate and low-grade gliomas for loss of heterozygosity on chromosome 10. 47/62 mostly malignant gliomas displayed complete loss of chromosome 10 and nine tumors were unaltered, whereas four glioblastomas and two low-grade oligodendrogliomas had partial loss on distal 10q. With these six tumors, we constructed a deletion map with increased marker density at 10q25-26 which shows two centromeric breakpoints at the markers D10S587 and D10S216, thus only confirming the distal, but not the proximal candidate glioblastoma suppressor locus. Two out of four low-grade oligodendrogliomas displayed partial deletions on 10q25-26. This suggests that deletion on chromosome 10 is not merely a late event in the progression of glioblastomas, but could play a role earlier in the development of gliomas.

Brain Neoplasms↗
PubMed1997

Inhibition of nonsense-mediated messenger RNA decay in clinical samples facilitates detection of human MSH2 mutations with an in vivo fusion protein assay and conventional techniques.

Germ-line mutations in the human MSH2 (hMSH2) gene account for about 40% of known defects in kindreds with hereditary nonpolyposis colon cancer. We describe a simple fusion protein assay for detection of hMSH2 nonsense mutations in yeast. Detection of nonsense mutations with this assay is severely compromised in many cases by nonsense-mediated mRNA decay, a physiological process that destabilizes the mutant RNA. Triggering of nonsense-mediated decay requires mRNA scanning by the ribosome to detect the stop codon. We show that treatment of cells with the translation inhibitor puromycin suppresses nonsense-mediated decay and facilitates the detection of nonsense mutations in clinical samples by cDNA sequencing, in vitro protein truncation tests, and the yeast fusion protein assay. Given the prevalence of chain-terminating mutations in human disease genes, puromycin treatment of blood samples should improve the signal-to-noise ratio and hence the sensitivity of many RNA-based diagnostic tests. Paradoxically, the yeast hMSH2::ADE2 fusion protein assay also detects some in-frame mutations, presumably through an effect on the folding of the fusion protein.

Blotting, Western↗
PubMed1997

[Genetic studies in neurology].

The use of either direct or indirect genetic analyses in neurology is becoming ever greater as more genes are identified thanks to the human genome project. Often the methodologies are complex and difficult to understand. The aim of this review is to present various approaches to molecular diagnosis using several different inherited neurological diseases as examples. These include inherited mitochondriopathies, monogenetic disorders like trinucleotid repeat instability syndromes, duplication anomalies and specific point mutations as well as heterogenetic diseases such as limb girdle dystrophy and familial amyotrophic lateral sclerosis. Possible pathogenetic implications can now be proposed as the basis of new therapeutic modalities.

Genetic Markers↗
PubMed1997

Disease expression in Swiss hereditary non-polyposis colorectal cancer (HNPCC) kindreds.

The genetics of Hereditary Non-Polyposis Colorectal Cancer (HNPCC) has recently been established and found to be associated with DNA mismatch repair deficiency. As the molecular basis of this syndrome does not appear to predict any particular disease, we compared families selected according to the "Amsterdam" criteria (AC) against families that were selected because of an aggregation of colonic and extracolonic malignancies (EC), all of which have been observed in HNPCC families. A comparison of the 2 groups revealed that there were significant differences between them. Age at disease onset for both groups was 20-30 years younger than in the general population; however, a normal age distribution was observed for the AC group whereas for the EC group a bimodal distribution was apparent. The prognosis for both groups together did not differ from that of the general population; however, if split, the AC group had a significantly better outcome than the EC group. Furthermore, dividing the AC group into hMSH2- and hMLH1-linked families revealed that there was no difference in severity of disease between these 2 groups with respect to survival and mean age of disease onset. Both the AC and EC groups displayed a similar tumour spectrum with a virtually identical tumour distribution. A significant finding was the over-representation, of brain tumours in this family set, which comprised the third most common malignancy after endometrial and stomach cancer.

Adult↗
PubMed1997

Identification of a modifier gene locus on chromosome 1p35-36 in familial adenomatous polyposis.

Phenotypic variability based on nonallelic heterogeneity is a characteristic feature of the dominantly inherited disease, familial adenomatous polyposis (FAP). A modifying locus, called Mom-1, which strongly influences disease expression has been mapped in the mouse model of FAP to the region of murine chromosome 4, which has synteny to human chromosome 1p35-36. In the present study, this chromosomal region was investigated by using 14 microsatellite markers within a large FAP kindred in which patients harbor the same germ-line mutation but show markedly different disease characteristics. The linkage program MLINK was used to determine whether any correlation exists between these markers and the development of extracolonic symptoms in polyposis coli patients. Depending on the mode of inheritance of the affected locus, a maximum lod score was observed for markers D1S211 and D1S197, reaching 2.08 and 1.77, respectively. The observed values obtained within one large FAP family are supportive of a phenotype-modifying locus within this chromosomal region.

Adenomatous Polyposis Coli↗
PubMed1997

BRCA1 mutations found in archived early onset breast tumours.

Inherited mutations in the BRCA1 gene are thought to account for approximately 5% of breast cancers in women under the age of 45 years. In order to determine whether mutations could be found at the expected frequency, 60% of the protein coding region of BRCA1 was screened in 75 archived early-onset breast tumours, taken from women under 45 years of age. Two of the 75 tumours (2.7%) had detectable mutations, in close agreement to that predicted. Since BRCA1 mutations found in breast tumours are invariably germline, two immediate consequences are apparent. Firstly, family members of affected patients are likely to carry mutations as well, and should be considered for BRCA1 screening; and secondly, persons harbouring a germline BRCA1 mutation should be examined frequently and indefinitely for new primary tumours in remaining breast tissue.

Adult↗
PubMed1997

Elevated frequency of p53-independent apoptosis after irradiation increases levels of DNA breaks in ataxia telangiectasia lymphoblasts.

Ataxia telangiectasia is a recessive generic disease featuring cerebellar degeneration, developmental abnormalities, high cancer risk, immunodeficiency, and radiosensitivity. Increased levels of unrepaired DNA breaks have been observed in irradiated ataxia telangiectasia cells compared to normal cells but no specific DNA break rejoining rate deficiency has been defined. Alterations in radiation-induced p53-dependent apoptosis have been reported for ataxia telangiectasia cells. This study investigated the radiation response of ataxia telangiectasia lymphoblastoid cells using the comet assay and uncovered a new feature of this technique, namely its capacity to preferentially detect living cells. It is shown here that early after exposure to gamma-rays, ataxia telangiectasia lymphoblasts exhibit an elevated frequency of cells committed to die via apoptosis. The observed apoptosis, which is likely to be independent of p53, leads to a higher number of DNA breaks during the first 3 h post irradiation in ataxia telangiectasia cells, relative to controls. Apart from cells undergoing apoptosis, ataxia telangiectasia lymphoblasts have an identical capacity to rejoin radiation-induced DNA breaks as controls. Results suggest that p53-independent apoptosis may contribute to the radiosensitivity and the immune defects of ataxia telangiectasia patients.

Adult↗
PubMed1997

Low frequency of BRCA1 germline mutations in 45 German breast/ovarian cancer families.

In this study we investigated 45 German breast/ovarian cancer families for germline mutations in the BRCA1 gene. We identified four germline mutations in three breast cancer families and in one breast-ovarian cancer family. among these were one frameshift mutation, one nonsense mutation, one novel splice site mutation, and one missense mutation. The missense mutation was also found in 2.8% of the general population, suggesting that it is not disease associated. The average age of disease onset in those families harbouring causative mutations was between 32.3 and 37.4 years, whereas the family harbouring the missense mutation had an average age of onset of 51.2 years. These findings show that BRCA1 is implicated in a small fraction of breast/ovarian cancer families suggesting the involvement of another susceptibility gene(s).

Adult↗
PubMed1997

BRCA1 and BRCA2 mutation analysis in 86 early onset breast/ovarian cancer patients.

Eighty-six women fulfilling specific selection criteria were studied for germline mutations in two breast cancer susceptibility genes, BRCA1 and BRCA2, using the protein truncation test (PTT). Nine germline mutations were identified, six in BRCA1 and three in BRCA2. Of the six BRCA1 mutations, three have previously been described and three are new, and for BRCA2, one is a new mutation and the other two appear to occur at a site that has been described several times. Four kindreds were breast cancer families, one a breast/ovarian cancer family, and the sixth an ovarian cancer family. The three kindreds with BRCA2 mutations were classified as one breast/ovarian cancer family, one breast cancer family, and one family which harboured one early onset breast cancer patient and two melanoma patients. The mutations in BRCA1 were either insertions, deletions, or transitions which all resulted in a premature stop codon. Mutations in BRCA2 were all frameshift mutations as a result of either 2 or 4 bp deletions. Two BRCA2 mutations were identical, suggesting a Swiss founder effect which was confirmed by haplotype sharing. The 10% mutation detection rate is compatible with the relaxed criteria used for patient selection. Considering the relative ease with which coding sequences can be screened by PTT, this assay is useful as a first screen for BRCA1 and BRCA2 mutations.

Adult↗
PubMed1997

TETRASPORE is required for male meiotic cytokinesis in Arabidopsis thaliana.

In flowering plants, male meiosis occurs in the microsporocyte to produce four microspores, each of which develops into a pollen grain. Here we describe four mutant alleles of TETRASPORE (TES), a gene essential for microsporocyte cytokinesis in Arabidopsis thaliana. Following failure of male meiotic cytokinesis in tes mutants, all four microspore nuclei remain within the same cytoplasm, with some completing their developmental programmes to form functional pollen nuclei. Both of the mitotic divisions seen in normal pollen development take place in tes mutants, including the asymmetric division required for the differentiation of gametes; some tes grains perform multiple asymmetric divisions in the same cytoplasm. tes pollen shows a variety of abnormalities subsequent to the cytokinetic defect, including fusion of nuclei, formation of ectopic internal walls, and disruptions to external wall patterning. In addition, ovules fertilized by tes pollen often abort, possibly because of excess paternal genomes in the endosperm. Thus tes mutants not only reveal a gene specific to male meiosis, but aid investigation of a wide range of processes in pollen development and function.

Alleles↗
PubMed1997

German family study on hereditary breast and/or ovarian cancer: germline mutation analysis of the BRCA1 gene.

Women harboring BRCA1 germline mutations carry an 85% lifetime risk of developing breast cancer and a 63% risk of ovarian cancer. In this first systematic study of familial breast and/or ovarian cancer in Germany we investigated 29 families for germline mutations in the BRCA1 gene. We identified mutations in three breast cancer families and in four breast-ovarian cancer families. The mutations include one missense mutation, one frameshift mutation, one splice mutation, and four nonsense mutations cosegregating with breast and/or ovarian susceptibility in five of ten (50%) families showing positive evidence of linkage to chromosome band 17q21 and in two of 19 (11%) families where linkage data was not available. Two apparently unrelated families carried the same nonsense mutation at codon 1835 and three families harbored a C to T transition at nucleotide 49 of the untranslated exon 4. Allelotyping of the markers D17S855, D17S1322, D17S1323, and D17S1327 located within or near BRCA1 revealed that all affected individuals in the two families harboring the mutation at codon 1835 shared at least one allele indicating a founder mutation. With respect to the overall mutation spectrum, no mutations were identified in exon 11 (0/7) in this set of German families. These findings differed significantly from those in British (17/32)(P = 0.012) and Southern Swedish (13/15) (P < 0.001) families. The lack of BRCA1 mutations in exon 11 which represents 61% of the entire coding sequence may provide additional insight into BRCA1 associated breast and ovarian tumor development.

BRCA1 Protein↗
PubMed1997

Cell death in perinatal hypoxic-ischaemic brain injury.

Perinatal hypoxic brain injury is a major cause of death and morbidity, in which the onset of injury can be prenatal, and the effects may be delayed. Selective neuronal necrosis, with isolated karyorrhectic nuclei in the pons, is a common pattern of injury in mature perinatal deaths. Other evidence implicates apoptosis in hypoxic brain injury. In this study the mode of cell death in hypoxic injury was investigated in 11 fresh stillbirths and 10 neonatal deaths. Sections of pons were stained using several methods including terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labelling (TUNEL) and immunocytochemistry. Karyorrhectic nuclei were counted on adjacent haemotoxylin and eosin sections. A high percentage of apoptotic cells was significantly associated with the presence of karyorrhexis in the pons, but there were five stillbirths in whom apoptosis in the pons was the sole evidence of hypoxic brain injury. PCNA positive neuronal nuclei were seen in 19 out of 21 cases. The results suggest that both apoptosis and necrosis are occurring following hypoxic injury, so that the pattern of injury in the pons may be better termed 'selective neuronal death'. Variations in severity and duration of the insult might explain the differences between cases. The presence of PCNA-positive neurons may suggest DNA repair in these nuclei, which might be activated at an early stage of apoptosis. However the precise mechanism by which apoptosis is induced in hypoxic brain injury remains to be elucidated.

Apoptosis↗
PubMed1996

Effects of intraoperative irradiation and intraoperative hyperthermia on canine sciatic nerve: neurologic and electrophysiologic study.

PURPOSE: Late radiation injury to peripheral nerve may be the limiting factor in the clinical application of intraoperative radiation therapy (IORT). The combination of IORT with intraoperative hyperthermia (IOHT) raises specific concerns regarding the effects on certain normal tissues such as peripheral nerve, which might be included in the treatment field. The objective of this study was to compare the effect of IORT alone to the effect of IORT combined with IOHT on peripheral nerve in normal beagle dogs. METHODS AND MATERIALS: Young adult beagle dogs were randomized into five groups of three to five dogs each to receive IORT doses of 16, 20, 24, 28, or 32 Gy to 5 cm of surgically exposed right sciatic nerve using 6 MeV electrons and six groups of four to five dogs each received IORT doses of 0, 12,16, 20, 24, or 28 Gy simultaneously with 44 degrees C of IOHT for 60 min. IOHT was performed using a water circulating hyperthermia device with a multichannel thermometry system on the surgically exposed sciatic nerve. Neurologic and electrophysiologic examinations were done before and monthly after treatment for 24 months. Electrophysiologic studies included electromyographic (EMG) examinations of motor function, as well as motor nerve conduction velocities studies. RESULTS: Two years after treatment, the effective dose for 50% complication (ED50) for limb paresis in dogs exposed to IORT only was 22 Gy. The ED50 for paresis in dogs exposed to IORT combined with IOHT was 15 Gy. The thermal enhancement ratio (TER) was 1.5. Electrophysiologic studies showed more prominent changes such as EMG abnormalities, decrease in conduction velocity and amplitude of the action potential, and complete conduction block in dogs that received the combination of IORT and IOHT. The latency to development of peripheral neuropathies was shorter for dogs exposed to the combined treatment. CONCLUSION: The probability of developing peripheral neuropathies in a large animal model was higher for IORT combined with IOHT, than for IORT alone. The dose required to produce the same level of late radiation injury to the sciatic nerve was reduced by a factor of 1.5 (TER) if IORT was combined with 44 degrees C of IOHT for 60 min.

Animals↗
PubMed1996

Secretory phospholipase A2 does not appear to be associated with phenotypic variation in familial adenomatous polyposis.

Recent studies in mice have provided strong evidence for a modifier gene that is capable of effecting the expression of the mouse equivalent of familial adenomatous polyposis (FAP). A candidate gene has been proposed, namely secretory phospholipase A2 (sPLA2). Increased tumor number in mice was correlated with low levels of sPLA2 expression and the presence of truncating mutations within the sPLA2 gene. In an attempt to determine whether any genetic alterations in the sPLA2 gene were associated with the expression of FAP in man, we investigated the genetic structure of sPLA2 in 97 polyposis coli patients presenting with various disease phenotypes, and its expression in 8 FAP patients displaying markedly different disease characteristics. In the current study no inactivating mutations in the sPLA2 gene were identified, suggesting that human sPLA2 is not associated with phenotypic variation in FAP.

Adenomatous Polyposis Coli↗
PubMed1996

Germline mutations in the 3' part of APC exon 15 do not result in truncated proteins and are associated with attenuated adenomatous polyposis coli.

Familial adenomatous polyposis (FAP) is an inherited predisposition to colorectal cancer characterized by the development of numerous adenomatous polyps predominantly in the colorectal region. Germline mutations in the adenomatous polyposis coli (APC) gene are responsible for most cases of FAP. Mutations at the 5' end of APC are known to be associated with a relatively mild form of the disease, called attenuated adenomatous polyposis coli (AAPC). We identified a frameshift mutation in the 3' part of exon 15, resulting in a stop codon at 1862, in a large Dutch kindred with AAPC. Western blot analysis of lymphoblastoid cell lines derived from affected family members from this kindred, as well as from a previously reported Swiss family carrying a frameshift mutation at codon 1987 and displaying a similar attenuated phenotype, showed only the wild-type APC protein. Our study indicates that chain-terminating mutations located in the 3' part of APC do not result in detectable truncated polypeptides and we hypothesize that this is likely to be the basis for the observed AAPC phenotype.

Adenomatous Polyposis Coli↗
PubMed1996

Familial infiltrative fibromatosis (desmoid tumours) (MIM135290) caused by a recurrent 3' APC gene mutation.

Desmoid tumours are generally very rare but occur about 100 times more frequently in the colorectal cancer predisposition syndrome familial adenomatous polyposis (MIM 175100), being represented in about 10% of patients. In addition to desmoid disease occurring in familial adenomatous polyposis (FAP) there exist familial infiltrative fibromatosis (MIM 135290) kindreds where there is no evidence of FAP. Previously we have described a kindred with familial infiltrative fibromatosis (FIF) in which desmoid tumours were associated with nonpolyposis colorectal cancer. FAP is caused by mutations in the APC gene and various genotype-phenotype relationships have been defined including reports that colorectal polyposis is less severe with mutations 5' to codon 157 and that the risk of desmoid tumours is high in FAP patients with APC gene mutations between codons 1444 and 1598. There is relatively little information on the phenotype of APC gene mutations 3' to codon 1598; however, one large family has been reported with a mutation at codon 1987 which presents with a highly variable phenotype which includes desmoid disease. We screened our original FIF kindred and three further families with a similar phenotype for mutations in the APC gene. A 4 bp frameshift deletion in codon 1962 was identified in the original FIF kindred and two further apparently unrelated families. Haplotype analysis suggests a common origin for the APC mutation in all three families. Affected individuals had no evidence of congenital hypertrophy of the retinal pigment epithelium. Colorectal polyposis was variable, and most affected patients had either none or a few late onset polyps. These findings demonstrate (i) that FAP and FIF are allelic, and (ii) that APC gene mutations which truncate the APC protein distal to the beta-catenin binding domain are associated with desmoid tumours, absent CHRPE and variable but attenuated polyposis expression.

Adenomatous Polyposis Coli Protein↗