Genetic variation exists for telomeric array organization within and among the genomes of normal, immortalized, and transformed chicken systems

Abstract

This study investigated telomeric array organization of diverse chicken genotypes utilizing in vivo and in vitro cells having phenotypes with different proliferation potencies. Our experimental objective was to characterize the extent and nature of array variation present to explore the hypothesis that mega-telomeres are a universal and fixed feature of chicken genotypes. Four different genotypes were studied including normal (UCD 001, USDA-ADOL Line 0), immortalized (DF-1), and transformed (DT40) cells. Both cytogenetic and molecular approaches were utilized to develop an integrated view of telomeric array organization. It was determined that significant variation exists within and among chicken genotypes for chromosome-specific telomeric array organization and total genomictelomeric sequence content. Although there was variation for mega-telomere number and distribution, two mega-telomere loci were in common among chicken genetic lines (GGA 9 and GGA W). The DF-1 cell line was discovered to maintain a complex derivative karyotype involving chromosome fusions in the homozygous and heterozygous condition. Also, the DF-1 cell line was found to contain the greatest amount of telomeric sequence per genome (17%) as compared to UCD 001 (5%) and DT40 (1.2%). The chicken is an excellent model for studying unique and universal features of vertebrate telomere biology, and characterization of the telomere length variation among genotypes will be useful in the exploration of mechanisms controlling telomere length maintenance in different cell types having unique phenotypes.

Molecular and Cellular Evidence for the Alternative Lengthening of Telomeres (ALT) Mechanism in Chicken

“…Telomeric PNA probe hybridization was performed to establish the cytogenetic telomeric profile of OU2 cells, as had been previously studied for the other cell types [O'Hare and Delany, 2009]. DF-1 and CEF001 samples were utilized as a point of comparison.…”

“…Telomeric lengths were analyzed according to O'Hare and Delany [2009] by the terminal restriction fragment (TRF) method. Briefly, restriction-digested DNA samples (150 ng) of DF-1, OU2, CEF001, and DT40 were separated by size on an agarose gel (0.7% agarose, 1 !…”

“…The OU2 cell line was investigated for its telomeric array profile to allow for comparisons with the other cell lines which were studied previously [O'Hare and Delany, 2009]. As per the cytogenetic analysis, the OU2 cell line lacks the size class of mega-telomere arrays found in other chicken genotypes [Delany et al, 2000;O'Hare and Delany, 2009], but shows evidence of moderately sized terminal telomeres and also interstitial arrays ( fig.…”

“…Interestingly, the immortalized chicken cell line DF-1 maintains an unusually large amount of heterogeneously sized telomeric DNA and greater than 3-fold more total telomeric sequence content than normal chicken cells [O'Hare and Delany, 2009]. Further, it was reported by Christman et al [2005] that telomerase activity was not detectable in the DF-1 cell line.…”

The Expression of Preaxial Polydactyly Is Influenced by Modifying Genetic Elements and Is Not Maintained by Chromosomal Inversion in an Avian Biomedical Model

“…At passage 3, chromosome harvests and cytogenetic slides were prepared and stored according to Delany et al [2007]. Also DT40, a transformed bursa lymphoma cell line [Baba et al, 1985] trisomic for GGA2 [Sonoda et al, 1998;Chang and Delany, 2004;O'Hare and Delany, 2009] was utilized for additional comparison regarding chromosome 2 status.…”