Biomedical subjects

Jian Xian

Publications and source records attributed to Jian Xian.

4 recordsLinked to original sources

PubMed2005

Somatic genetic changes accompanying lung tumor development.

Carcinomas are believed to develop by incremental steps of increasingly abnormal morphology driven by accumulating somatic genetic changes. This process is often difficult to study, as the early stages are undetectable. We used fluorescence bronchoscopy, which enhances detection of preinvasive bronchial lesions, and have obtained sequential biopsies of carcinoma in situ (CIS) from a patient with no detectable tumor and from a squamous cell carcinoma that developed 19 months after presentation at the site of one of the previous CIS lesions. Biopsies of preinvasive CIS, which follow-up showed had different pathologic outcomes, and tumor were microdissected to obtain enriched cell populations and DNA prepared from them. Molecular characteristics of these biopsies were compared by loss of heterozygosity analysis, TP53 mutation analysis, and comparative genomic hybridization. Although all lesions examined had the same TP53 mutation and almost identical allelotypes, differences were observed. Loss in 5q21 and amplification of 3q25-26 were associated with the lesion that progressed and the subsequent carcinoma. Allele loss at 4p16 was detected in the tumor but not in any of the CIS lesions, suggesting it was a late event associated with tumor invasion. Amplification at 4q12 was specifically observed in the tumor and in the CIS at the site of eventual tumor formation. Although these findings may be unique to this one patient, the successful demonstration of sequential genetic changes raises the possibility that this approach, unencumbered by interpatient variability between lesions, will greatly facilitate the identification of molecular events driving the invasive process

Adult↗

PubMed2004

Targeted disruption of the 3p12 gene, Dutt1/Robo1, predisposes mice to lung adenocarcinomas and lymphomas with methylation of the gene promoter.

The DUTT1 gene is located on human chromosome 3, band p12, within a region of nested homozygous deletions in breast and lung tumors. It is therefore a candidate tumor suppressor gene in humans and is the homologue (ROBO1) of the Drosophila axonal guidance receptor gene, Roundabout. We have shown previously that mice with a targeted homozygous deletion within the Dutt1/Robo1 gene generally die at birth due to incomplete lung development: survivors die within the first year of life with epithelial bronchial hyperplasia as a common feature. Because Dutt1/Robo1 heterozygous mice develop normally, we have determined their tumor susceptibility. Mice with a targeted deletion within one Dutt1/Robo1 allele spontaneously develop lymphomas and carcinomas in their second year of life with a 3-fold increase in incidence compared with controls: invasive lung adenocarcinomas are by far the predominant carcinoma. In addition to the mutant allele, loss of heterozygosity analysis indicates that these tumors retain the structurally normal allele but with substantial methylation of the gene's promoter. Substantial reduction of Dutt1/Robo1 protein expression in tumors is observed by Western blotting and immunohistochemistry. This suggests that Dutt1/Robo1 is a classic tumor suppressor gene requiring inactivation of both alleles to elicit tumorigenesis in these mice.

Adenocarcinoma↗

PubMed2003

Block in development at the pre-B-II to immature B cell stage in mice without Ig kappa and Ig lambda light chain.

Silencing individual C (constant region) lambda genes in a kappa(-/-) background reduces mature B cell levels, and L chain-deficient (lambda(-/-)kappa(-/-)) mice attain a complete block in B cell development at the stage when L chain rearrangement, resulting in surface IgM expression, should be completed. L chain deficiency prevents B cell receptor association, and L chain function cannot be substituted (e.g., by surrogate L chain). Nevertheless, precursor cell levels, controlled by developmental progression and checkpoint apoptosis, are maintained, and B cell development in the bone marrow is fully retained up to the immature stage. L chain deficiency allows H chain retention in the cytoplasm, but prevents H chain release from the cell, and as a result secondary lymphoid organs are B cell depleted while T cell levels remain normal.

Animals↗

PubMed2002

Cre-loxP chromosome engineering of a targeted deletion in the mouse corresponding to the 3p21.3 region of homozygous loss in human tumours.

Chromosomal deletions are a common feature of epithelial tumours and when further defined by homozygous deletions, are often the location of tumour suppressor genes. Deletions within the short arm of chromosome 3 occur very frequently in human carcinomas: a minimal region of loss at 3p21.3 (the Luca) region has been defined by overlapping homozygous deletions in lung and breast cancer cell lines. Using a rapid strategy for Cre-loxP chromosome engineering, a deletion of approximately 370 kb was created in the mouse germline corresponding to the deleted region at 3p21.3. The deletion when homozygous is embryonic lethal. Heterozygotes develop normally despite being haplo-insufficient for twelve genes including the candidate tumour suppressor gene Rassf1. Because damage to 3p21.3 often occurs very early in the sequence of genetic changes that lead to malignancy, particularly in lung and breast cancer, further genetic damage to these mice will provide the opportunity to model multi-step tumorigenesis of these tumours.

Animals↗