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Xin Xiang

Publications and source records attributed to Xin Xiang.

13 recordsLinked to original sources
PubMed2006

A +TIP for a smooth trip.

Is there a cellular mechanism for preventing a depolymerizing microtubule track from "slipping out from under" its cargo? A recent study in budding yeast indicates that when a chromosome is transported to the minus end of a spindle microtubule, its kinetochore-bound microtubule plus end-tracking protein (+TIP) Stu2 may move to the plus end to promote rescue; i.e., to switch the depolymerizing end to a polymerizing end. The possibility that other +TIPs may play a similar role in sustaining a microtubule track during vesicular transport deserves investigation.

Animals↗
PubMed2006

Motor proteins at the microtubule plus-end.

The plus-end of the microtubule has a central role in the interactions that occur between the microtubule and actin cytoskeletons. The recent identification of a family of proteins that congregate at the plus-end is enabling an increased mechanistic understanding of how this cross talk is accomplished. These proteins, termed plus-end tracking proteins because they appear to associate with the plus-end as it grows, have already been shown to regulate microtubule dynamics and to facilitate the formation of connections between the plus-end and the actin-rich cortex. Several motor proteins, including an actin-based motor, microtubule-based motors that move towards either end of the microtubule and microtubule motors that depolymerize microtubule ends, can now be added to the list of plus-end tracking proteins. Here, we discuss how the presence of these motors at the plus-end seems to drive several fundamental cellular processes involving force generation at the interface between microtubule ends and the cortex, vesicle translocation following search and capture, microtubule disassembly and the delivery of signals to the cortex that govern actin assembly and cell polarity.

Animals↗
PubMed2006

CLIP-170 homologue and NUDE play overlapping roles in NUDF localization in Aspergillus nidulans.

Proteins in the cytoplasmic dynein pathway accumulate at the microtubule plus end, giving the appearance of comets when observed in live cells. The targeting mechanism for NUDF (LIS1/Pac1) of Aspergillus nidulans, a key component of the dynein pathway, has not been clear. Previous studies have demonstrated physical interactions of NUDF/LIS1/Pac1 with both NUDE/NUDEL/Ndl1 and CLIP-170/Bik1. Here, we have identified the A. nidulans CLIP-170 homologue, CLIPA. The clipA deletion did not cause an obvious nuclear distribution phenotype but affected cytoplasmic microtubules in an unexpected manner. Although more microtubules failed to undergo long-range growth toward the hyphal tip at 32 degrees C, those that reached the hyphal tip were less likely to undergo catastrophe. Thus, in addition to acting as a growth-promoting factor, CLIPA also promotes microtubule dynamics. In the absence of CLIPA, green fluorescent protein-labeled cytoplasmic dynein heavy chain, p150(Glued) dynactin, and NUDF were all seen as plus-end comets at 32 degrees C. However, under the same conditions, deletion of both clipA and nudE almost completely abolished NUDF comets, although nudE deletion itself did not cause a dramatic change in NUDF localization. Based on these results, we suggest that CLIPA and NUDE both recruit NUDF to the microtubule plus end. The plus-end localization of CLIPA itself seems to be regulated by different mechanisms under different physiological conditions. Although the KipA kinesin (Kip2/Tea2 homologue) did not affect plus-end localization of CLIPA at 32 degrees C, it was required for enhancing plus-end accumulation of CLIPA at an elevated temperature (42 degrees C).

Amino Acid Sequence↗
PubMed2005

Cytoplasmic dynein's mitotic spindle pole localization requires a functional anaphase-promoting complex, gamma-tubulin, and NUDF/LIS1 in Aspergillus nidulans.

In Aspergillus nidulans, cytoplasmic dynein and NUDF/LIS1 are found at the spindle poles during mitosis, but they seem to be targeted to this location via different mechanisms. The spindle pole localization of cytoplasmic dynein requires the function of the anaphase-promoting complex (APC), whereas that of NUDF does not. Moreover, although NUDF's localization to the spindle poles does not require a fully functional dynein motor, the function of NUDF is important for cytoplasmic dynein's targeting to the spindle poles. Interestingly, a gamma-tubulin mutation, mipAR63, nearly eliminates the localization of cytoplasmic dynein to the spindle poles, but it has no apparent effect on NUDF's spindle pole localization. Live cell analysis of the mipAR63 mutant revealed a defect in chromosome separation accompanied by unscheduled spindle elongation before the completion of anaphase A, suggesting that gamma-tubulin may recruit regulatory proteins to the spindle poles for mitotic progression. In A. nidulans, dynein is not apparently required for mitotic progression. In the presence of a low amount of benomyl, a microtubule-depolymerizing agent, however, a dynein mutant diploid strain exhibits a more pronounced chromosome loss phenotype than the control, indicating that cytoplasmic dynein plays a role in chromosome segregation.

Anaphase↗
PubMed2004

[Operational line of laparoscopic liver resections].

OBJECTIVE: To evaluate the feasibility and indications of laparoscopic liver resections. METHODS: Twenty-seven patients with liver lesions, 17 men and 10 women, aged 31 - 67, including 14 cases of primary liver cancer, 6 cases of liver hemangioma, 2 cases of liver abscess, 1 case of hilar carcinoma, 1 case of hepatic adenoma, 1 case of hepatic focal nodular hyperplasia, 1 case of liver inflammatory granuloma, and 1 case of infected liver cyst, underwent laparoscopic liver resection, partial liver resection in 17 cases and anatomical left liver resections in 10 cases, consecutively from July 2002 to April 2003. The clinical data were analyzed. RESULTS: All of the 27 operations were performed smoothly with an average operation time of 184 min and the average blood loss during operation of 441 ml. The average postoperative hospital stay was 5 days. No complication occurred. CONCLUSION: A promising minimally invasive technique, laparoscopic liver resection can be carried out safely and effectively by experienced surgeons as one of the first choices for the loci limited to left liver and part of the loci in right liver.

Adult↗
PubMed2004

Nuclear migration and positioning in filamentous fungi.

Genetic analyses of nuclear distribution mutants have indicated that functions of the microtubule motor, cytoplasmic dynein, and its regulators are important for nuclear positioning in filamentous fungi. Here we review these studies and also present the need to further dissect how dynein and its associated microtubule cytoskeleton are involved mechanistically in nuclear positioning in the multinucleated hyphae.

Aspergillus nidulans↗
PubMed2003

Spindle formation in Aspergillus is coupled to tubulin movement into the nucleus.

In many important organisms, including many algae and most fungi, the nuclear envelope does not disassemble during mitosis. This fact raises the possibility that mitotic onset and/or exit might be regulated, in part, by movement of important mitotic proteins into and out of the nucleoplasm. We have used two methods to determine whether tubulin levels in the nucleoplasm are regulated in the fungus Aspergillus nidulans. First, we have used benomyl to disassemble microtubules and create a pool of free tubulin that can be readily observed by immunofluorescence. We find that tubulin is substantially excluded from interphase nuclei, but is present in mitotic nuclei. Second, we have observed a green fluorescent protein/alpha-tubulin fusion in living cells by time-lapse spinning-disk confocal microscopy. We find that tubulin is excluded from interphase nuclei, enters the nucleus seconds before the mitotic spindle begins to form, and is removed from the nucleoplasm during the M-to-G1 transition. Our data indicate that regulation of intranuclear tubulin levels plays an important, perhaps essential, role in the control of mitotic spindle formation in A. nidulans. They suggest that regulation of protein movement into the nucleoplasm may be important for regulating mitotic onset in organisms with intranuclear mitosis.

Aspergillus↗
PubMed2003

LIS1 at the microtubule plus end and its role in dynein-mediated nuclear migration.

The cytoplasmic dynein complex and its accessory dynactin complex are involved in many cellular activities including nuclear migration in fungi (for review see Karki and Holzbaur, 1999). LIS1, the product of a causal gene for human lissencephaly (smooth brain), has also been implicated in dynein function based on studies in fungi and more recent studies in higher eukaryotic systems (for review see Gupta et al., 2002). Exactly how LIS1 may regulate the behavior of cytoplasmic dynein in various organisms is a fascinating question. In this issue, Lee et al. (2003) describe important new findings in Saccharomyces cerevisiae regarding the role of LIS1 (Pac1) in dynein-mediated nuclear migration.

Cell Movement↗
PubMed2003

Cytoskeleton and motor proteins in filamentous fungi.

In filamentous fungi, the actin cytoskeleton is required for polarity establishment and maintenance at hyphal tips and for formation of a contractile ring at sites of septation. Recently, formins have been identified as Arp (actin-related protein) 2/3-independent nucleators of actin polymerization, and filamentous fungi contain a single formin that localizes to both sites. Work on cytoplasmic dynein and members of the kinesin and myosin families of motors has continued to reveal new information regarding the function and regulation of motors as well as demonstrate the importance of microtubules in the long-distance transport of vesicles/organelles in the filamentous fungi.

Aspergillus↗
PubMed2003

The requirement of the LC8 dynein light chain for nuclear migration and septum positioning is temperature dependent in Aspergillus nidulans.

In the filamentous fungus Aspergillus nidulans, the multisubunit motor complex cytoplasmic dynein plays essential roles in nuclear migration and septum positioning. The 8 kDa light chain, LC8, the smallest subunit, is conserved among eukaryotic organisms. Besides being a component in the dynein complex, LC8 also interacts with a wide spectrum of mammalian and viral proteins. To date, the function of this small polypeptide is not well understood. To address this issue, we have created a deletion mutation (DeltanudG) at the nudG locus encoding LC8 in A. nidulans. At 42 degrees C, the DeltanudG mutant forms minute colonies lacking asexual reproduction: this phenotype resembles the phenotype of the dynein heavy chain null mutant. The mutant nuclei largely clustered in the spore body after conidial germination, and the septum was often assembled distally toward the hyphal apex, whereas a control germling has its nuclei distributed along the hypha and the septum formed near the spore body. When the mutant was grown at 23 degrees C, however, its colony resembled a control one, and so did the patterns of nuclear distribution and septum positioning. Elevation of the growth temperature gradually reduced colony size and abolished asexual sporulation. After a period of growth at 23 degrees C that allowed the nuclei to move out of the spore end, a temperature shift to 42 degrees C prevented newly divided nuclei from migrating apart, suggesting that LC8/NUDG was required for both initiating and maintaining dynein motor functions at elevated temperatures. A functional GFP-NUDA fusion was used to test whether LC8/NUDG is required for DHC (dynein heavy chain)/NUDA localization. We found that at 23 degrees C GFP-NUDA localized to the hyphal apex and the septation site in DeltanudG cells as in control cells. Such localizations were absent at 42 degrees C in mutant cells, but not in control cells. We conclude that LC8 plays a role in DHC localization/function, and the requirement for such a role in A. nidulans cells is temperature dependent.

Aspergillus nidulans↗
PubMed2003

Accumulation of cytoplasmic dynein and dynactin at microtubule plus ends in Aspergillus nidulans is kinesin dependent.

The mechanism(s) by which microtubule plus-end tracking proteins are targeted is unknown. In the filamentous fungus Aspergillus nidulans, both cytoplasmic dynein and NUDF, the homolog of the LIS1 protein, localize to microtubule plus ends as comet-like structures. Herein, we show that NUDM, the p150 subunit of dynactin, also forms dynamic comet-like structures at microtubule plus ends. By examining proteins tagged with green fluorescent protein in different loss-of-function mutants, we demonstrate that dynactin and cytoplasmic dynein require each other for microtubule plus-end accumulation, and the presence of cytoplasmic dynein is also important for NUDF's plus-end accumulation. Interestingly, deletion of NUDF increases the overall accumulation of dynein and dynactin at plus ends, suggesting that NUDF may facilitate minus-end-directed dynein movement. Finally, we demonstrate that a conventional kinesin, KINA, is required for the microtubule plus-end accumulation of cytoplasmic dynein and dynactin, but not of NUDF.

Aspergillus nidulans↗
PubMed2002

Cytoplasmic dynein intermediate chain and heavy chain are dependent upon each other for microtubule end localization in Aspergillus nidulans.

The multisubunit microtubule motor, cytoplasmic dynein, targets to various subcellular locations in eukaryotic cells for various functions. The cytoplasmic dynein heavy chain (HC) contains the microtubule binding and ATP binding sites for motor function, whereas the intermediate chain (IC) is implicated in the in vivo targeting of the HC. Concerning any targeting event, it is not known whether the IC has to form a complex with the HC for targeting or whether the IC can target to a site independently of the HC. In the filamentous fungus Aspergillus nidulans, the dynein HC is localized to the ends of microtubules near the hyphal tip. In this study, we demonstrate that our newly identified dynein IC in A. nidulans is also localized to microtubule ends and is required for HC's localization to microtubule ends in living cells. With the combination of two reagents, an HC loss-of function mutant and the green fluorescent protein (GFP)-fused IC that retains its function, we show that the IC's localization to microtubule ends also requires HC, suggesting that cytoplasmic dynein HC-IC complex formation is important for microtubule end targeting. In addition, we show that the HC localization is not apparently altered in the deletion mutant of NUDF, a LIS1-like protein that interacts directly with the ATP-binding domain of the HC. Our study suggests that, although HC-IC association is important for the targeting of dynein to microtubule ends, other essential components, such as NUDF, may interact with the targeted dynein complex to produce full motor activities in vivo.

Amino Acid Sequence↗