Ontogeny-Driven rDNA Rearrangement, Methylation, and Transcription, and Paternal Influence

Gene rearrangement occurs during development in some cell types and this genome dynamics is modulated by intrinsic and extrinsic factors, including growth stimulants and nutrients. This raises a possibility that such structural change in the genome and its subsequent epigenetic modifications may also take place during mammalian ontogeny, a process undergoing finely orchestrated cell division and differentiation. We tested this hypothesis by comparing single nucleotide polymorphism-defined haplotype frequencies and DNA methylation of the rDNA multicopy gene between two mouse ontogenic stages and among three adult tissues of individual mice. Possible influences to the genetic and epigenetic dynamics by paternal exposures were also examined for Cr(III) and acid saline extrinsic factors. Variables derived from litters, individuals, and duplicate assays in large mouse populations were examined using linear mixed-effects model. We report here that active rDNA rearrangement, represented by changes of haplotype frequencies, arises during ontogenic progression from day 8 embryos to 6-week adult mice as well as in different tissue lineages and is modifiable by paternal exposures. The rDNA methylation levels were also altered in concordance with this ontogenic progression and were associated with rDNA haplotypes. Sperm showed highest level of methylation, followed by lungs and livers, and preferentially selected haplotypes that are positively associated with methylation. Livers, maintaining lower levels of rDNA methylation compared with lungs, expressed more rRNA transcript. In vitro transcription demonstrated haplotype-dependent rRNA expression. Thus, the genome is also dynamic during mammalian ontogeny and its rearrangement may trigger epigenetic changes and subsequent transcriptional controls, that are further influenced by paternal exposures

Loss of heterozygosity on chromosome 14 in primary nasopharyngeal carcinoma

Multiple genetic alterations are believed to be involved in the pathogenesis of nasopharyngeal carcinomas (NPC). Loss of heterozygosity (LOH) of chromosomes 3p, 9p and 11q were previously reported in NPC. In order to further define the genetic alterations in NPC, 42 pairs of normal and tumor DNA of NPC were examined for LOH on chromosomes 5p, 5q, 6q, 14q, 15q, 16p, 16q, 17q using 16 polymorphic microsatellite markers. Frequent LOH (33%; 7 out of 21 cases) was observed in chromosome 14q at locus D14s81 (14q31). In order to define the common region of deletion, nine polymorphic microsatellite markers on 14q were examined for LOH in NPC. A common region of deletion was defined in NPC at chromosome 14q24.3-q32.1 flanked by two microsatellite markers D14s76 and D14s45. The common region of deletion (14q24.3-32.1) identified in NPC overlapped with the deleted regions of 14q reported in several human cancers. In 2 cases of NPC, the pattern of LOH revealed the presence of another commonly deleted region defined by loci D14s63 and D14s69 (mapped to 14q11.1-24.1) and located proximal to locus D14s76 (14q24.3). This study suggests that multiple tumor suppressor genes present on chromosome 14q are involved in the pathogenesis of NPC.link_to_subscribed_fulltex

Telomerase activation in human cancers

Objective To review the background of telomerase activation and the methodology involved in its determination, and the clinico-pathological significance of telomerase activation in human cancers. Data sources An English-language literature search using MEDLINE (1966-1997) and bibliographic reviews of textbooks and review articles. Results Progressive shortening of telomeres was associated with continuous cell division in normal somatic cells. Telomerase was activated in most cancer cells and immortal germ cells to maintain their telomeric lengths. The occurrence and clinical pathological significance of telomerase activation was evaluated in various types of human cancer. Conclusions Telomerase activation is a common event in human cancers and may be as a useful marker for malignant cells. Telomerase may also be a therapeutic target for cancer treatment.link_to_subscribed_fulltex

Clinical significance of telomerase activation and telomeric restriction fragment (TRF) in cervical cancer

Telomerase activation was examined in 50 cases of cervical cancer, 27 normal cervix and five cervical cancer cell lines using the sensitive polymerase chain reaction (PCR)-based TRAP (telomeric repeat amplification protocol) assay. Telomeric restriction fragment (TRF) length of these specimens was measured by Southern hybridisation. Telomerase activation was common in cervical cancers and was detected in 46/50 cases (92%). Telomerase activity was weak in normal cervix and was detected only in 2/27 cases (7.4%). Telomerase activity was detected in all stages of cervical cancer suggesting that it is an early event in cancer progression. The clinical significance of telomerase activation was analysed in 47 squamous cell carcinoma of the cervix. High telomerase activity was more frequently detected in advanced diseases (100% in stage III and stage IV cervical cancers combined) compared with early diseases (68.6% in stage I and stage II cancers combined). The difference was statistically significant (P < 0.02). Telomerase activity was not statistically correlated with other clinical parameters examined. This is the first report of telomeric length in human cervical cancer. Both shortening and elongation of TRF length in cervical cancers was observed. Advanced cervical cancers tended to have a wider range of variation of TRF length compared with early disease and normal cervix. There was no obvious relationship between TRF length and the clinical parameters examined including clinical staging, differentiation status of tumour, human papilloma virus (HPV) infection, recurrence rate, tumor size and invasion depth. The clinical significance of TRF length appears to be limited in cervical cancers. Our results indicate that telomerase activity is closely associated with tumor cells and may be useful as a marker for detection of tumor cells in cervical biopsies.link_to_subscribed_fulltex