Telomere Variation in Xenopus laevis

ABSTRACT

Eukaryotic telomeres are variable at several levels, from the length of the simple sequence telomeric repeat tract in different cell types to the presence or number of telomere-adjacent DNA sequence elements in different strains or individuals. We have investigated the sequence organization of Xenopus laevis telomeres by use of the vertebrate telomeric repeat (TTAGGG) _n and blot hybridization analysis. The (TTAGGG) _n -hybridizing fragments, which ranged from less than 10 to over 50 kb with frequently cutting enzymes, defined a pattern that was polymorphic between individuals. BAL 31 exonuclease treatment confirmed that these fragments were telomeric. The polymorphic fragments analyzed did not hybridize to 5S RNA sequences, which are telomeric according to in situ hybridization. When telomeric fragments from offspring (whole embryos) were compared to those from the spleens of the parents, the inheritance pattern of some bands was found to be unusual. Furthermore, in one cross, the telomeres of the embryo were shorter than the telomeres of the parents’ spleen, and in another, the male’s testis telomeres were shorter than those of the male’s spleen. Our data are consistent with a model for chromosome behavior that involves a significant amount of DNA rearrangement at telomeres and suggest that length regulation ofXenopus telomeres is different from that observed forMus spretus and human telomeres.

ACKNOWLEDGMENTS

We thank Titia de Lange and Sandya Narayanswami for providing probes, the Ruben and Black labs for frogs, members of the Black laboratory for assistance and advice with frog procedures, and Keith Karoly, Steve Black, and Liz Blackburn for helpful discussions or comments.

This work was supported by a grant from the Oregon Health Sciences Foundation (Medical Research Foundation of Oregon) to J.S. and by a grant to Reed College under the Howard Hughes Medical Institute Undergraduate Biological Sciences Initiative.