spRap1 and spRif1, recruited to telomeres by Taz1, are essential for telomere function in fission yeast

AbstractTelomeres are essential for genome integrity. scRap1 (S. cerevisiae Rap1) directly binds to telomeric DNA [1–3] and regulates telomere length and telomere position effect (TPE) [4–6] by recruiting two different groups of proteins to its RCT (Rap1 C-terminal) domain [7]. The first group, Rif1 and Rif2, regulates telomere length [8, 9]. The second group, Sir3 and Sir4 [10], is involved in heterochromatin formation [11–13]. On the other hand, human TRF1 and TRF2, as well as their fission yeast homolog, Taz1, directly bind to telomeric DNA [14–16] and negatively regulate telomere length [16–20]. Taz1 also plays important roles in TPE and meiosis [16, 20, 21]. Human Rap1, the ortholog of scRap1, negatively regulates telomere length and appears to be recruited to telomeres by interacting with TRF2 [7]. Here, we describe two novel fission yeast proteins, spRap1 (S. pombe Rap1) and spRif1 (S. pombe Rif1), which are orthologous to scRap1 and scRif1, respectively. spRap1 and spRif1 are independently recruited to telomeres by interacting with Taz1. The rap1 mutant is severely defective in telomere length control, TPE, and telomere clustering toward the spindle pole body (SPB) at the premeiotic horsetail stage, indicating that spRap1 has critical roles in these telomere functions. The rif1 mutant also shows some defects in telomere length control and meiosis. Our results indicate that Taz1 provides binding sites for telomere regulators, spRap1 and spRif1, which perform the essential telomere functions. This study establishes the similarity of telomere organization in fission yeast and humans

Oral administration of a fruiting body extract of Boletopsis leucomelas enhances intestinal IgA production in LPS-challenged mice

The present study showed that a hot water extract of the fruiting body of the edible mushroom Boletopsis leucomelas, known as 'Kurokawa' Japanese, strongly stimulated IgA-production in mouse spleen cells in our screening experiment. The in vivo study was also conducted with the objective of enhancing adaptive immune response by oral administration of the hot water extract of B. leucomelas (BLE) in lipopolysaccharide (LPS)-challenged mice. The mice were fed a standard diet with or without 0.16% BLE. The mice were also orally administered sodium phosphate buffer or LPS weekly at days 7, 14 and 21. Results indicated that LPS-specific serum IgG, IgM and IgA were increased in the BLE diet group compared to the standard diet group. Interestingly, intestinal total IgA and LPS-specific IgA were significantly increased in the BLE diet group. Moreover, the <1000 Da, 5000-10,000 Da phenol sulphate-positive molecules from BLE showed significant IgA-producing activity.ArticleFOOD AND AGRICULTURAL IMMUNOLOGY. 25(4):510-522 (2014)journal articl

Giantin Affects Golgi Stack Connection

Golgins are a family of Golgi-localized long coiled-coil proteins. The major golgin function is thought to be the tethering of vesicles, membranes, and cytoskeletal elements to the Golgi. We previously showed that knockdown of one of the longest golgins, Giantin, altered the glycosylation patterns of cell surfaces and the kinetics of cargo transport, suggesting that Giantin maintains correct glycosylation through slowing down transport within the Golgi. Giantin knockdown also altered the sizes and numbers of mini Golgi stacks generated by microtubule de-polymerization, suggesting that it maintains the independence of individual Golgi stacks. Therefore, it is presumed that Golgi stacks lose their independence following Giantin knockdown, allowing easier and possibly increased transport among stacks and abnormal glycosylation. To gain structural insights into the independence of Golgi stacks, we herein performed electron tomography and 3D modeling of Golgi stacks in Giantin knockdown cells. Compared with control cells, Giantin-knockdown cells had fewer and smaller fenestrae within each cisterna. This was supported by data showing that the diffusion rate of Golgi membrane proteins is faster in Giantin-knockdown Golgi, indicating that Giantin knockdown structurally and functionally increases connectivity among Golgi cisternae and stacks. This increased connectivity suggests that contrary to the cis-golgin tether model, Giantin instead inhibits the tether and fusion of nearby Golgi cisternae and stacks, resulting in transport difficulties between stacks that may enable the correct glycosylation of proteins and lipids passing through the Golgi

The Golgin Protein Giantin Regulates Interconnections Between Golgi Stacks

Golgins are a family of Golgi-localized long coiled-coil proteins. The major golgin function is thought to be the tethering of vesicles, membranes, and cytoskeletal elements to the Golgi. We previously showed that knockdown of one of the longest golgins, Giantin, altered the glycosylation patterns of cell surfaces and the kinetics of cargo transport, suggesting that Giantin maintains correct glycosylation through slowing down transport within the Golgi. Giantin knockdown also altered the sizes and numbers of mini Golgi stacks generated by microtubule de-polymerization, suggesting that it maintains the independence of individual Golgi stacks. Therefore, it is presumed that Golgi stacks lose their independence following Giantin knockdown, allowing easier and possibly increased transport among stacks and abnormal glycosylation. To gain structural insights into the independence of Golgi stacks, we herein performed electron tomography and 3D modeling of Golgi stacks in Giantin knockdown cells. Compared with control cells, Giantin-knockdown cells had fewer and smaller fenestrae within each cisterna. This was supported by data showing that the diffusion rate of Golgi membrane proteins is faster in Giantin-knockdown Golgi, indicating that Giantin knockdown structurally and functionally increases connectivity among Golgi cisternae and stacks. This increased connectivity suggests that contrary to the cis-golgin tether model, Giantin instead inhibits the tether and fusion of nearby Golgi cisternae and stacks, resulting in transport difficulties between stacks that may enable the correct glycosylation of proteins and lipids passing through the Golgi

Fission yeast Stn1 maintains stability of repetitive DNA at subtelomere and ribosomal DNA regions

Telomere binding protein Stn1 forms the CST (Cdc13/CTC1-STN1-TEN1) complex in budding yeast and mammals. Likewise, fission yeast Stn1 and Ten1 form a complex indispensable for telomere protection. We have previously reported that stn1-1, a high-temperature sensitive mutant, rapidly loses telomere DNA at the restrictive temperature due to frequent failure of replication fork progression at telomeres and subtelomeres, both containing repetitive sequences. It is unclear, however, whether Stn1 is required for maintaining other repetitive DNAs such as ribosomal DNA. In this study, we have demonstrated that stn1-1 cells, even when grown at the permissive temperature, exhibited dynamic rearrangements in the telomere-proximal regions of subtelomere and ribosomal DNA repeats. Furthermore, Rad52 and γH2A accumulation was observed at ribosomal DNA repeats in the stn1-1 mutant. The phenotypes exhibited by the stn1-1 allele were largely suppressed in the absence of Reb1, a replication fork barrier-forming protein, suggesting that Stn1 is involved in the maintenance of the arrested replication forks. Collectively, we propose that Stn1 maintains the stability of repetitive DNAs at subtelomeres and rDNA regions