Seo, Beomseok et al. (2015) International Worm Meeting "Telomere maintenance through recruitment of internal genomic regions."

Seo, Beomseok, Hills, Mark, Oh, Hyun-Seok, Lee, Junho, Sung, Sanghyun, Kim, Chuna, Shim, Jaegal, Choi, Rachael Mi Jung, Kim, Eunkyeong, Lim, Daisy S., Chun, Jongsik, Kim, Hyesook

[International Worm Meeting, 2015]

Telomere is a ribonucleoprotein complex that protects the natural ends of the linear chromosome. Telomere length is mainly maintained by telomerase, a reverse transcriptase that adds telomere repeat sequence. However recombination-dependent mechanism for telomere maintenance also exist in yeast and human cancer cells. In Caenorhabditis elegans, some of telomerase deletion mutant, trt-1(ok410), can maintain the telomere by alternative lengthening of telomeres (ALT). However the molecular mechanism of ALT in worms is largely unknown. In this study, we established stably maintained ALT survivors of worms that activate an ALT mechanism to escape from the sterility phenotype caused by telomerase deletion. By whole genome sequencing and mapping we concluded that mutation may not be required to maintain ALT telomere in these survivors. Interestingly, ALT survivors added either of two specific internal genomic regions as templates for ALT(T-ALT) according to their genetic backgrounds. A T-ALT sequence consists of telomere-like repeat sequence with unrelated sequence in between. T-ALTs had already been copied to a proximal telomere region of the same chromosome prior to ALT activation in nature, and were amplified interchromosomally by ALT activation. Here we propose a hypothesis that the existence of T-ALT structure in the proximal telomere may be one of the prerequisites for ALT activation..

BeomSeok Seo et al. (2008) C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting "Dissecting Alternative Lengthening of Telomeres in Caenorhabditis elegans"

Junho Lee, BeomSeok Seo

[C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting, 2008]

Eukaryotes have linear chromosomes which causes ''the end-replication problem''. This is solved by telomerase which adds telomeric repeats to the end of the chromosomes. However, it was found that telomeres can be maintained without telomerase in yeast and cancer cells. This is called Alternative Lengthening of Telomere(ALT), which is presumed to be based on a process involving recombination. In Caenorhabditis elegans, it is known that trt-1 telomerase deficient mutant become sterile after several generations. We mutagenized trt-1 mutant worms and screened suppressor mutants which survived without telomerase. The Terminal Restriction Fragments (TRF) assay revealed that telomere length was lengthened and heterogeneous. Currently we are mapping suppressor mutants with single nucleotide polymorphism(SNP).

Kim, Chuna et al. (2011) International Worm Meeting "Telomere lengthening in suppressor mutants of telomerase deficient Caenorhabditis elegans."

Lee, Junho, Kim, Chuna, Seo, Beomseok

[International Worm Meeting, 2011]

Eukaryotic cells have linear chromosomes which cause 'the end-replication problem'. With telomeres, the chromosomal ends can be protected from degradation or fusion with another chromosome. Telomeres of somatic cells are gradually shortened with repeated replication. However, telomeres of cancer cells and germ cells are not shortened because they can maintain telomere length by the telomerase, which is a special kind of reverse transcriptase. However, it was also found that telomeres can be maintained without telomerase in yeast and some cancer cells by the Alternative Lengthening of Telomere (ALT) mechanism, which is based on a process involving recombination. But, until now, the mechanism that may suppress ALT in telomerase-negative cells have not been known. Therefore, we performed forward and reverse genetic screenings for finding ALT suppressor. In Caenorhabditis elegans it was known that the trt-1(ok410) mutant strain, which lacks the telomerase catalytic subunit, becomes sterile (mortal germline phenotype) after several generations as a result of shortening of telomeres. We mutagenized trt-1(ok410) mutant animals and isolated suppressor mutants that had re-acquired immortality of germ cells. With Terminal Restriction Fragments(TRF) assay, Single Telomere Length Analysis(STELA) and Fluorescence In Situ Hybridization(FISH), we found that the telomeres of the suppressor mutants were lengthened and had distinct property from normal telomeres. Currently, we are mapping these suppressor mutants by Single Nucleotide Polymorphisms(SNPs) and whole genome sequencing technology.

Sung, Sanghyun et al. (2013) International Worm Meeting "in vivo isolation of telomeric proteins in the nematode Caenorhabditis elegans."

Seo, Beomseok, Sung, Sanghyun, Lee, Junho

[International Worm Meeting, 2013]

Telomeres are special nucleoprotein complexes that cap the ends of the eukaryotic linear chromosomes to maintain genomic integrity. Many interesting aspects of the telomeres of Caenorhabditis elegans have been studied; for example, the extension of organismic lifespan by longer telomeres and alternative lengthening of telomeres at the organismic level have been reported. It is conceivable that the protein components of the telomeres may have critical roles in these processes as regulators of length, stability, and yet unknown interesting mechanisms of telomeres. Because most telomeric proteins found in higher mammals (or even yeasts) do not have homologous partners in C. elegans, there is a strong need for biochemical approaches to identify them in C. elegans. Previously, we used a nucleic acid affinity capture method to isolate specific proteins associated with telomeric DNA. Although this in vitro method was useful, it had limitations for describing all proteins that may act in the in vivo context. Therefore, in this study, we utilized the recently developed technique called proteomics of isolated chromatin segments(PICh). PICh uses unique nucleic acid to capture the endogenous segments of chromatin which are fixed before hybridization, so it can be a direct and quantitative tool. Currently, we are investigating the telomere-specific proteins of wild type C. elegans.

Kim, Chun-A et al. (2009) International Worm Meeting "Dissecting Alternative Lengthening of Telomeres in Caenorhabditis elegans ."

Seo, Beomseok, Lee, Junho, Kim, Chun-A

[International Worm Meeting, 2009]

Eukaryotic cells have linear chromosomes which is protected by telomeres. Telomeres are distinguished from the double strand breaks (DSBs) which is a kind of DNA damage. With telomeres, the chromosomal ends can be protected from degradation or fusion with another chromosome. Telomeres of somatic cells are gradually shortened with repeated replication. However, telomeres of cancer cells and germ cells are not shortened because they can maintain telomere length by the telomerase, a special kind of reverse transcriptase. In Caenorhabditis elegans it was known that trt-1(ok410) mutant that lacks telomerase catalytic subunit has shortened telomeres and fused chromosomes. These data correspond with the study of mammals and it is known that telomere maintenance mechanisms are evolutionally conserved. However, in other model organisms like yeast and mouse, telomerase independent telomere maintenance mechanism has been reported; This is called Alternative Lengthening of Telomeres (ALT). ALT mechanism is used in about 15% of cancer cells. The telomere repeat numbers of ALT cells are heterogeneous. Some ALT cells show non-traditional telomere repeats with other sequence inserted. Loss-of-function experiments suggested that ALT mechanism is based on homologous recombination-mediated replication. So far, the existence of ALT mechanism has not been confirmed at the organismal level. Recently, we have found novel suppressor mutants of trt-1(ok410) mutant by EMS mutagenesis screening. Currently we are mapping the suppressor mutation by Single Nucleotide Polymorphisms(SNPs) mapping method that uses SNPs of restriction endonuclease recognition site as a canonical mapping marker. By mapping the putative ALT genes using this approach, we expect to elucidate the molecular mechanisms of ALT.

Flynn, Elizabeth et al. (2019) International Worm Meeting "A Role for Apoptosis and Glycogen Storage in the Fertility Response to High-Glucose Diet."

Guilbo, Katherine, Mondoux, Michelle, Flynn, Elizabeth, Engstrom , Amanda

[International Worm Meeting, 2019]

Over the past several decades, sugar consumption has increased worldwide, contributing to the rise of obesity and type 2 diabetes. Both diseases are correlated with a variety of health problems, including a decrease in fertility. As in humans, a high-glucose diet decreases fertility in C. elegans. Although this has been shown by multiple labs, the cellular mechanisms that regulate this response to glucose are unknown. Glucose affects many cellular functions and pathways that could contribute to this decrease in fertility. One such pathway is the storage of glucose as glycogen, the main glucose storage polymer in both C. elegans and humans. We hypothesized that hermaphrodite C. elegans may have decreased fertility on a high-glucose diet because of an increase in glycogen storage. Both a high glucose diet and increased glycogen have been shown to have negative effects on lifespan in C. elegans (Gusarov et al. 2017; Seo et al. 2018). We found that decreasing glycogen storage using a mutant in the glycogen synthase enzyme (gsy-1) led to an overall decrease in fertility in hermaphrodites; however, a high-glucose diet did not further reduce fertility in a gsy-1 mutant. This suggests that glycogen storage plays a role in both lifespan regulation and fertility in C. elegans. A second pathway that may regulate the fertility response to a high glucose diet is apoptosis. Previously, it has been show that germline apoptosis increases in the C. elegans hermaphrodites in response to different environmental stressors. We hypothesized that glucose could act as an environmental stressor. We found that decreased hermaphrodite fertility on a high-glucose diet is dependent on the core apoptotic proteins CED-3 and CED-4. Currently, we are working to understand which apoptotic pathway is activated on a high-glucose diet. We have characterized this apoptosis response to glucose in both sexes and found it to be hermaphrodite specific. Through our work we hope to better understand the diverse cellular mechanisms which contribute to decreased fertility on a high-glucose diet.