Measuring vertebrate telomeres: applications and limitations

Telomeres are short tandem repeated sequences of DNA found at the ends of eukaryotic chromosomes that function in stabilizing chromosomal end integrity. In vivo studies of somatic tissue of mammals and birds have shown a correlation between telomere length and organismal age within species, and correlations between telomere shortening rate and lifespan among species. This result presents the tantalizing possibility that telomere length could be used to provide much needed information on age, ageing and survival in natural populations where longitudinal studies are lacking. Here we review methods available for measuring telomere length and discuss the potential uses and limitations of telomeres as age and ageing estimators in the fields of vertebrate ecology, evolution and conservation

Applications of Strand-Specific in situ Hybridization

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Fluorescence in situ hybridization (FISH) is used to determine the location of specific DNA sequences on chromosomes. It is an effective tool in genomic mapping and is finding increasing use in medical diagnosis. A ''strand-specific'' version of FISH has been developed in the Life Sciences Division of LANL. The new procedure, named CO-FISH, reveals not only location but also the 5'-to-3'direction of a target sequence, such as the sense strand of a gene. This project was designed to investigate applications of the new technique. Strand-specific FISH was found to be useful and informative for genomic mapping of repetitive DNA sequences. The method provide a valuable new tool for investigating the mechanisms of aneuploidy inducing agents and the cytogenetic phenomena called lateral asymmetry. Finally, using strand-specific FISH, the authors were able to detect certain types of chromosome aberrations (isochromosomes, inversions and Robertsonian translocations) that can be difficult to observe with standard techniques

Rapid generation of chromosome-specific alphoid DNA probes using the polymerase chain reaction

Non-isotopic in situ hybridization of chromosome-specific alphoid DNA probes has become a potent tool in the study of numerical aberrations of specific human chromosomes at all stages of the cell cycle. In this paper, we describe approaches for the rapid generation of such probes using the polymerase chain reaction (PCR), and demonstrate their chromosome specificity by fluorescence in situ hybridization to normal human metaphase spreads and interphase nuclei. Oligonucleotide primers for conserved regions of the alpha satellite monomer were used to generate chromosome-specific DNA probes from somatic hybrid cells containing various human chromosomes, and from DNA libraries from sorted human chromosomes. Oligonucleotide primers for chromosome-specific regions of the alpha satellite monomer were used to generate specific DNA probes for the pericentromeric heterochromatin of human chromosomes 1, 6, 7, 17 and X directly from human genomic DNA

Comparative chromosome painting discloses homologous Segments in distantly related mammals

Comparative chromosome painting, termed ZOO-FISH, using DNA libraries from flow sorted human chromosomes 1,16,17 and X, and mouse chromosome 11 discloses the presence of syntenic groups in distantly related mammalian Orders ranging from primates (Homo sapiens), rodents (Mus musculus), even-toed ungulates (Muntiacus muntjak vaginalis and Muntiacus reevesi) and whales (Balaenoptera physalus). These mammalian Orders have evolved separately for 55-80 million years (Myr). We conclude that ZOO-FISH can be used to generate comparative chromosome maps of a large number of mammalian species

Short Telomeres in Hatchling Snakes: Erythrocyte Telomere Dynamics and Longevity in Tropical Pythons

Telomere length (TL) has been found to be associated with life span in birds and humans. However, other studies have demonstrated that TL does not affect survival among old humans. Furthermore, replicative senescence has been shown to be induced by changes in the protected status of the telomeres rather than the loss of TL. In the present study we explore whether age- and sex-specific telomere dynamics affect life span in a long-lived snake, the water python (Liasis fuscus)

Chromosomal localization of the 18S-28S and 5S rRNA genes and (TTAGGG)n sequences of butterfly lizards (Leiolepis belliana belliana and Leiolepis boehmei, Agamidae, Squamata)

Chromosomal mapping of the butterfly lizards Leiolepis belliana belliana and L. boehmei was done using the 18S-28S and 5S rRNA genes and telomeric (TTAGGG)n sequences. The karyotype of L. b. belliana was 2n = 36, whereas that of L. boehmei was 2n = 34. The 18S-28S rRNA genes were located at the secondary constriction of the long arm of chromosome 1, while the 5S rRNA genes were found in the pericentromeric region of chromosome 6 in both species. Hybridization signals for the (TTAGGG)n sequence were observed at the telomeric ends of all chromosomes, as well as interstitially at the same position as the 18S-28S rRNA genes in L. boehmei. This finding suggests that in L. boehmei telomere-to-telomere fusion probably occurred between chromosome 1 and a microchromosome where the 18S-28S rRNA genes were located or, alternatively, at the secondary constriction of chromosome 1. The absence of telomeric sequence signals in chromosome 1 of L. b. belliana suggested that its chromosomes may have only a few copies of the (TTAGGG)n sequence or that there may have been a gradual loss of the repeat sequences during chromosomal evolution

Inheritance of Telomere Length in a Bird

Telomere dynamics are intensively studied in human ageing research and epidemiology, with many correlations reported between telomere length and age-related diseases, cancer and death. While telomere length is influenced by environmental factors there is also good evidence for a strong heritable component. In human, the mode of telomere length inheritance appears to be paternal and telomere length differs between sexes, with females having longer telomeres than males. Genetic factors, e.g. sex chromosomal inactivation, and non-genetic factors, e.g. antioxidant properties of oestrogen, have been suggested as possible explanations for these sex-specific telomere inheritance and telomere length differences. To test the influence of sex chromosomes on telomere length, we investigated inheritance and sex-specificity of telomere length in a bird species, the kakapo (Strigops habroptilus), in which females are the heterogametic sex (ZW) and males are the homogametic (ZZ) sex. We found that, contrary to findings in humans, telomere length was maternally inherited and also longer in males. These results argue against an effect of sex hormones on telomere length and suggest that factors associated with heterogamy may play a role in telomere inheritance and sex-specific differences in telomere length