Worm Breeder's Gazette 12(2): 33 (January 1, 1992)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
The ends of C. elegans chromosomes adopt "centromere" functions for meiotic disjunction; one end being involved in holding the bivalent together and the other probably providing a site for the attachment of microtubules. These roles do not appear to be end specific as either end of the chromosome can be the inner or outer end of the bivalent (WBG 10(3), 143). Chromosome ends terminate in telomere sequences consisting of a repeating T- and G-rich strand running 5'-3' towards the outer end of the chromosome and the complementary C- and A-rich strand running 5'-3' towards the interior of the chromosome. In C. elegans the telomere appears to be made up of repeats of TTAGGC (Wicky et al., Meeting Abstracts 1991, p. 339). Although telomeres are required to maintain the integrity of the chromosome, it is the pro-terminal sequences, situated inside the telomeres that are thought to function in the attachment of the chromosome to the nuclear scaffold or matrix, and to have centromere and ARS properties. Thus, these pro-terminal sequences may be important for meiotic disjunction in C. elegans.
In order to characterize the ends of the chromosomes, candidate pro-terminal sequences were generated by a PCR based method from the telomere sequence, TTAGGC and its complement. The sequences that were obtained have not been characterized, but were mapped to the YAC "polytene" filters. The dots in the figure indicate sites of hybridization with TTAGGC-containing probes. The sites were clustered towards the ends of the chromosome, but were also found in the middle of LGs I and III. Sites were rare on the X. Most of these sites were recognized by probing with the extension product from the (GCCTAA)4 primer and a smaller set by the (TTAGGC)4 primed product. These internal "telomere" sequences might be remnants of fusions between chromosomes, while those at the ends of the chromosome may have been generated by recombination errors.
Other repeated sequences have been mapped to the YAC filters (Coulson, personal communication), including C erep3 (Felsenstein & Emmons, Mol. Cell Biol. 8, 875 (1988); LaVolpe, personal communication) and show a similar, but not identical distribution. In situ hybridization has also identified other repeated sequences mapping predominantly to the ends of chromosomes. These repeats may all form part of the pro-terminal portions of the chromosomes and may have various roles in maintaining the distribution of chromosomes in the nucleus and at the time of division.
[Figure excluded due to low reproducability]