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

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 genomic-telomeric 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

Bovine telomere dynamics and the association between telomere length and productive lifespan

Average telomere length (TL) in blood cells has been shown to decline with age in a range of vertebrate species, and there is evidence that TL is a heritable trait associated with late-life health and mortality in humans. In non-human mammals, few studies to date have examined lifelong telomere dynamics and no study has estimated the heritability of TL, despite these being important steps towards assessing the potential of TL as a biomarker of productive lifespan and health in livestock species. Here we measured relative leukocyte TL (RLTL) in 1,328 samples from 308 Holstein Friesian dairy cows and in 284 samples from 38 female calves. We found that RLTL declines after birth but remains relatively stable in adult life. We also calculated the first heritability estimates of RLTL in a livestock species which were 0.38 (SE = 0.03) and 0.32 (SE = 0.08) for the cow and the calf dataset, respectively. RLTL measured at the ages of one and five years were positively correlated with productive lifespan (p < 0.05). We conclude that bovine RLTL is a heritable trait, and its association with productive lifespan may be used in breeding programmes aiming to enhance cow longevity

Chromosome passenger complex is required for the survival of cells with ring chromosomes in fission yeast.

Ring chromosomes are circular chromosomal abnormalities that have been reported in association with some genetic disorders and cancers. In Schizosaccharomyces pombe, lack of function of protection of telomere 1 (Pot1) or telomerase catalytic subunit (Trt1) results in survivors with circular chromosomes. Hitherto, it is poorly understood how cells with circular chromosomes survive and how circular chromosomes are maintained. Fission yeast Cut17/Bir1, Ark1, Pic1, and Nbl1 is a conserved chromosome passenger complex (CPC) functioning mainly throughout mitosis. Here, using a temperature-sensitive mutant of CPC subunits, we determined that CPC is synthetically lethal in combination with either Pot1 or Trt1. The pot1Δ pic1-T269 double mutant, which has circular chromosomes, showed a high percentage of chromosome mis-segregation and DNA damage foci at 33°C. We furthermore found that neither Shugoshin Sgo2 nor heterochromatin protein Swi6, which contribute to the centromeric localization of CPC, were required for the survival in the absence of Pot1. Both the pot1Δ sgo2Δ and pot1Δ swi6Δ double mutants displayed a high percentage of DNA damage foci, but a low percentage of chromosome mis-segregation, suggesting the link between the high percentage of chromosome mis-segregation and the lethality of the CPC pot1Δ double mutant. Our results suggest that CPC is required for the survival of cells with circular chromosomes and sheds light on the possible roles of CPC in the maintenance of circular chromosomes