Biomedical subjects

Hugo Maruyama

Publications and source records attributed to Hugo Maruyama.

3 recordsLinked to original sources

PubMed2005

Uncoupling of longevity and telomere length in C. elegans.

The nematode Caenorhabditis elegans, after completing its developmental stages and a brief reproductive period, spends the remainder of its adult life as an organism consisting exclusively of post-mitotic cells. Here we show that telomere length varies considerably in clonal populations of wild-type worms, and that these length differences are conserved over at least ten generations, suggesting a length regulation mechanism in cis. This observation is strengthened by the finding that the bulk telomere length in different worm strains varies considerably. Despite the close correlation of telomere length and clonal cellular senescence in mammalian cells, nematodes with long telomeres were neither long lived, nor did worm populations with comparably short telomeres exhibit a shorter life span. Conversely, long-lived daf-2 and short-lived daf-16 mutant animals can have either long or short telomeres. Telomere length of post-mitotic cells did not change during the aging process, and the response of animals to stress was found independent of telomere length. Collectively, our data indicate that telomere length and life span can be uncoupled in a post-mitotic setting, suggesting separate pathways for replication-dependent and -independent aging.

Aging↗

PubMed2004

Molecular mechanisms of DNA end-loop formation by TRF2.

In the telomere region of human chromosomes, the (TTAGGG)n sequence stretches over several kilobases and forms a distinct higher-order structure with various proteins. Telomere repeat binding factors (TRFs) bind specifically to this sequence and play critical roles in the maintenance of telomere structure and function. Here, we prepared a series of linear DNA carrying a stretch of telomeric sequence ((TTAGGG)n, approximately 1.8 (kb) with different end-structures and observed their higher-order complexes with TRFs by atomic force microscopy. TRF2 molecules exclusively bound to the telomeric DNA region at several different places simultaneously mainly as a dimer, and often mediated DNA loop formation by forming a tetramer at the root. These multiple-binding, multimerization and DNA loop formation by TRF2 were observed regardless of the DNA-end structure (blunt, 3'-overhanging, telomeric, non-telomeric). However, when the DNA end carried the telomeric-3'-overhanging region, the loop was frequently formed at the end of the DNA. Namely, the TRF2-mediated DNA loop formation is independent of the end-structure and the 3'-overhanging TTAGGG sequence is responsible for the stabilization of the loop. TRF1 also bound to the telomeric DNA as a dimer, but did not mediate DNA loop formation by itself. These results provide a new insight into the molecular mechanism of DNA end-loop formation by TRFs.

Binding Sites↗

PubMed2002

Chromatin reconstitution: development of a salt-dialysis method monitored by nano-technology.

The regulation of DNA replication and transcription is achieved by dynamic structural changes of chromatin in which a series of proteins will acquire accessibility to specific regions of the DNA strand. A combination of biochemistry and nano-technology is essential to address questions regarding the structural basis for such macromolecular mechanisms. In the present study, we established an efficient salt-dialysis method of chromatin reconstitution and employed atomic force microscopy (AFM) as a single-molecule-imaging technique, to monitor the efficiency of the reconstitution. At first, the reconstitution efficiency with short DNA molecules of several kilo-base pairs was low, although the salt dialysis yielded a "beads-on-a-string" structure of oligonucleosomes with each nucleosome trapping 158+/-27 bp DNA. However, the efficiency for nucleosome formation became higher when longer DNA molecules with a super-helical constraint were used. A statistical analysis of the obtained AFM images identified a first-order relationship between the efficiency of the reconstitution and the length of the super-coiled DNA used. A high efficiency of approximately 290 bp/nucleosome that is close to the in vivo situation was obtained with a approximately 100 kbp template DNA. This enabled the structure-function studies of long chromatin molecules under well-defined conditions.

Chromatin↗