Biomedical subjects

R G Li

Publications and source records attributed to R G Li.

7 recordsLinked to original sources

PubMed2001

Restriction fragment length polymorphism markers associated with silk maysin, antibiosis to corn earworm (Lepidoptera: Noctuidae) larvae, in a dent and sweet corn cross.

Maysin, a C-glycosylflavone in maize silk, has insecticidal activity against corn earworm, Helicoverpa zea (Boddie), larvae. Sweet corn, Zea mays L., is a vulnerable crop to ear-feeding insects and requires pesticide protection from ear damage. This study was conducted to identify maize chromosome regions associated with silk maysin concentration and eventually to transfer and develop high silk maysin sweet corn lines with marker-assisted selection (MAS). Using an F2 population derived from SC102 (high maysin dent corn) and B31857 (low maysin sh2 sweet corn), we detected two major quantitative trait loci (QTL). It was estimated that 25.6% of the silk maysin variance was associated with segregation in the genomic region of npi286 (flanking to p1) on chromosome 1S. We also demonstrated that a1 on chromosome 3L had major contribution to silk maysin (accounted for 15.7% of the variance). Locus a1 has a recessive gene action for high maysin with the presence of functional p1 allele. Markers umc66a (near c2) and umc105a on chromosome 9S also were detected in this analysis with minor contribution. A multiple-locus model, which included npi286, a1, csu3 (Bin 1.05), umc245 (Bin 7.05), agrr21 (Bin 8.09), umc105a, and the epistatic interactions npi286 x a1, a1 x agrr21, csu3 x umc245, and umc105a x umc245, accounted for 76.3% of the total silk maysin variance. Tester crosses showed that at the a1 locus, SC102 has functional A1 alleles and B31857 has homozygous recessive a1 alleles. Individuals of (SC102 x B31857) x B31857 were examined with MAS and plants with p1 allele from SC102 and homozygous a1 alleles from B31857 had consistent high silk maysin. Marker-assisted selection seems to be a suitable method to transfer silk maysin to sweet corn lines to reduce pesticide application.

Alleles↗

PubMed1995

Genetic alterations at 5p15: a potential marker for progression of precancerous lesions of the uterine cervix.

BACKGROUND: Development of uterine cervical cancer is preceded by preneoplastic proliferative changes in the cervical epithelium called "intra-epithelial neoplasia" or "dysplasia." The genetic basis of the origin and progression of such preneoplastic lesions is not known. By analysis of carcinomas for loss of constitutional heterozygosity (LOH), we have previously shown a high frequency of allelic loss in the short arm of chromosome 5 (5p), suggesting loss of a candidate tumor suppressor gene located in 5p and associated with the development of this tumor. PURPOSE: To further understand the role of genetic alterations that affect 5p in cervical carcinogenesis, we evaluated the status of microsatellite polymorphisms at five loci mapped to 5p14-ter in precancerous and cancerous lesions. METHODS: Biopsy specimens from two groups of patients were analyzed for genetic alterations affecting 5p. One group comprised 14 cases of precancerous lesions (i.e., dysplasias) and five cases of carcinoma in situ (CIS); the second group comprised 46 previously untreated patients with invasive carcinoma. Tumor and normal DNAs were analyzed by polymerase chain reaction for genetic losses and instability at five polymorphic microsatellite loci (D5S392, D5S406, D5S208, D5S117, and D5S432) mapped to 5p. RESULTS: LOH was observed in 25 (55.6%) of 45 informative invasive carcinomas, one (20%) of five cases of CIS, and three (21%) of 14 precancerous lesions. Among the loci tested, D5S406 (5p15.1-15.2) exhibited LOH in 12 (48%) of 25 invasive carcinomas, one (33%) of three cases of CIS, and three (60%) of five precancerous lesions, suggesting this to be the site in 5p of the novel candidate tumor suppressor gene. In addition, replication error-type alterations were noted in the 5p14-ter region in six (13%) of 46 invasive carcinomas, two (40%) of five cases of CIS, and three (21%) of 14 precancerous lesions. Instability affected D5S406 in eight (66.7%) of 12 instances that showed microsatellite instability. CONCLUSION: These observations suggest that allelic loss and microsatellite instability in the region of D5S406 may play a role early in the development of cervical carcinoma and identify the site of a candidate tumor suppressor gene. These genetic markers (allelic loss and microsatellite instability) may also define CIS and precancerous lesions at high risk for progression to invasive cancer. IMPLICATIONS: The future molecular cloning of the candidate tumor suppressor gene at 5p15.1-15.2 may provide new insights into the genetic mechanisms of cervical carcinogenesis. Analysis and clinical follow-up of a large cohort of prospectively ascertained cases of precancerous lesions would help to validate the usefulness of these markers.

Biomarkers, Tumor↗

PubMed1994

TP53 gene mutations and CCND1 gene amplification in head and neck squamous cell carcinoma cell lines.

Mutations of the tumor-suppressor gene TP53 and amplification of CCND1 gene have been reported to occur frequently in head and neck squamous cell carcinomas (HNSQCC). In experimental systems, TP53 mutations have been shown to lead to genomic instability, including an increased propensity for gene amplification. We have examined 16 HNSQCC cell lines for the association between TP53 over-expression/mutation and CCND1 amplification. p53 over-expression was detected in 50% of the cell lines by immunohistochemistry using the monoclonal antibody (MAb) PAb1801. TP53 mutations were also detected in 50% of the cell lines by analysis of single-strand conformation polymorphism (SSCP) and DNA sequencing of exons 4 through 9. Six cell lines showed TP53 mutations and over-expression of the protein, 2 cell lines showed TP53 mutations but no p53 expression, and 2 cell lines showed over-expression of p53 protein but no TP53 gene mutations. CCND1 amplification was found in 38% of the cell lines by Southern blot analysis. Only 1 cell line showed both TP53 mutation and CCND1 amplification, whereas 7 of 8 cell lines with TP53 mutations had no CCND1 amplification. pRb expression was detected by Western blot analysis, and the level of pRb did not correlate with either CCND1 amplification or TP53 mutation. Our findings suggest that TP53 mutation and CCND1 amplification are common genetic alterations in HNSQCC and that the occurrence of either genetic event may be sufficient to abrogate normal cell cycle control.

Carcinoma, Squamous Cell↗

PubMed1994

Allelotype analysis of cervical carcinoma.

To identify the genetic events which may play a role in the development of cervical carcinoma, we performed a detailed allelotype analysis utilizing DNA from 53 primary tumors and corresponding normal cells and 57 polymorphic probes mapped to each of the chromosomal arms, excluding the short arms of the acrocentric chromosomes. Loss of heterozygosity (LOH) of > 25% was observed at sites on 11 chromosomal arms, which included 1q (26%), 3p (35%), 3q (31%), 4q (46%), 5p (53%), 5q (38%), 6p (28%), 10q (28%), 11p (42%), 18p (38%), and Xq (26%). The most frequent LOH was noted on 4q (ADH3) and 5p (D5S19), suggesting that loss of candidate tumor suppressor genes on these chromosomal arms may play a role in the development of cervical carcinoma. The two sites of deletions identified on 5p and Xq represent novel candidate tumor suppressor gene sites which have so far not been reported in any other tumor type. Human papilloma virus status did not correlate with any of the sites which showed frequent LOH. TP53 mutation analysis by single-strand conformation polymorphism analysis was performed in 17 tumors that either showed 17p deletions (TP53, D17S5, or D17S28) or were human papilloma virus negative. One of the 7 human papilloma virus-negative tumors, which also showed LOH at the D17S28 locus, had a mutation in exon 5. This study represents the first comprehensive genetic analysis of this cancer and identifies several novel features of significance to genetic etiology of cervical carcinoma.

Adult↗

PubMed1994

Replication error-type genetic instability at 1q42-43 in human male germ cell tumors.

The replication error phenotype, recognized as microsatellite sequence alterations, has recently been suggested to be associated with hereditary nonpolyposis colorectal cancer and other types of sporadic tumors. We examined paired tumor-normal DNAs from 69 human male germ cell tumors for somatic instability at the 1q42-43 region. Analysis of a variable number of tandem repeats marker (D1S74) and 3 (CA)n type microsatellite loci (D1S235, D1S180, and angiotensinogen) revealed genetic alterations in tumor DNAs of 26 (38.2%) cases. The changes observed comprised rearrangements with D1S74 detected by Southern blot analysis in 4 of 55 (7%) cases; replication error-type alterations with D1S235, D1S180, and angiotensinogen in 12 of 66 (18.2%) cases; and loss of heterozygosity in 12 of 67 (17.9%) cases with the same probes. The microsatellite sequence alterations were more common in histological subsets other than teratomas, while the loss of heterozygosity was significantly more frequent in teratomas compared to other histologies. These results suggest that microsatellite instability and loss of heterozygosity at 1q42-43 may be unrelated genetic events which may play a role in germ cell tumor development.

Chromosomes, Human, Pair 1↗

PubMed1994

Frequent allelic deletions and loss of expression characterize the DCC gene in male germ cell tumors.

The DCC tumor suppressor gene has been shown to be frequently deleted or its expression reduced or absent in colorectal, gastro-intestinal, pancreatic, prostatic, and breast carcinomas, and glioblastomas. By allelotype analysis using the DCC-flanking polymorphic marker D18S5 we have previously shown that allelic deletions at 18q21 occur in 40% of male germ cell tumors (Murty et al., 1994). In order to further understand the role of DCC gene in germ cell tumorigenesis, we evaluated deletions by loss of heterozygosity (LOH) and mRNA expression by RT-PCR in tumor tissues and cell lines. Analysis of 61 paired normal-tumor DNAs using the probes D18S5, JOSH 4.4 (a polymorphism within the DCC locus) and a (CA)n polymorphism in an intron of DCC revealed that 45% of GCTs had allelic deletions. In addition, two homozygous deletions were found in the DCC gene among 91 (61 used in the LOH analysis and an additional 30) tumor DNAs when screened with the cDNA probes (pDCC 1.65, pDCC 1.9 and pDCC 1.0). By RT-PCR analysis of four normal testes, nine GCT cell lines and 14 tumor tissues, DCC gene expression was detected in all four normal testes, while four (45%) GCT cell lines and one (7%) tumor specimen showed lack of expression. In addition, DCC expression was highly reduced in three (21%) tumor tissues. The high frequency of LOH at 18q21 was characteristic of seminomas as well as all subsets of non-seminomas in primary as well as metastatic states. Frequent allelic loss in all histologic subsets, homozygous deletions, and loss of expression of DCC suggest that suppression of this gene's function is an early event in GCT development.

Alleles↗

PubMed1991

Bone remodeling in hypervitaminosis D3. Radiologic-microangiographic-pathologic correlations.

To investigate the mechanism of bone changes in hypervitaminosis D3, we compared contact radiographs, microangiograms by injection of Chinese ink, and corresponding histopathologic macrosections of 66 rabbits that received different doses of vitamin D3. In early stages, radiographs showed subperiosteal bone resorption and porotic cortical bone. The corresponding microangiograms showed proliferating vessels in the periosteum and cortical bone with associated dilatation of the Haversian and Volkmann's canals. When metastatic calcification fills these intracortical caverns or the intertrabecular spaces in the metaphysis and physis, the bone shows a diffuse increased density on radiographs. A dense band in the metaphysis reflects a thickening of calcified chondromatrix due to a hypotrophy of the distal metaphyseal capillaries. Six to 12 weeks after vitamin D3 withdrawal, radiographs showed further increased density of the cortical bone, due to newly formed bone and metastatic calcification. Alternating bands of increased and decreased density in the metaphysis and physis reflect the reinvasion of normal vasculature between growth cartilage and calcified chondromatrix, with normalization of endochondral ossification.

Angiography↗