The conserved kinase SRPK regulates karyosome formation and spindle microtubule assembly in Drosophila oocytes

Advance Online Publication August 1, 2012 doi: 10.1242/?jcs.107979 In Drosophila oocytes, after the completion of recombination, meiotic chromosomes form a compact cluster called the karyosome within the nucleus, and later assemble spindle microtubules without centrosomes. Although these oocyte specific phenomena are also observed in humans, their molecular basis is not well understood. Here we report essential roles for the conserved kinase SRPK in both karyosome formation and spindle microtubule assembly in oocytes. We have identified a female sterile srpk mutant through a cytological screen for karyosome defects. Unlike most karyosome mutants, the karyosome defect is independent of the meiotic recombination checkpoint. Heterochromatin clustering found within the wild-type karyosome is disrupted in the mutant. Strikingly, a loss of SRPK severely prevents microtubule assembly for acentrosomal spindles in mature oocytes. Subsequently, bi-orientation and segregation of meiotic chromosomes are also defective. Therefore, this study demonstrates new roles of this conserved kinase in two independent meiotic steps specific to oocytes.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Share Alike License, which permits unrestricted non-commercial use, distribution and reproduction in any medium provided that the original work is properly cited and all further distributions of the work or adaptation are subject to the same Creative Commons License terms.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Rab11 regulates exocytosis of recycling vesicles at the plasma membrane

Advance Online Publication June 8, 2012 doi: 10.1242/?jcs.102913 Senye Takahashi, Keiji Kubo, Satoshi Waguri, Atsuko Yabashi, Hye-Won Shin, Yohei Katoh and Kazuhisa Nakayama*?*Corresponding author: Kazuhisa Nakayama, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; Phone: +81-75-753-4527; Fax: +81-75-753-4557; E-mail: kazunaka{at}pharm.kyoto-u.ac.jp. Rab11 is known to associate primarily with perinuclear recycling endosomes and regulate recycling of endocytosed proteins. However, the recycling step in which Rab11 participates remains unknown. We here show that, in addition to causing tubulation of recycling endosomes, Rab11 depletion gives rise to accumulation of recycling carriers containing endocytosed transferrin and transferrin receptor beneath the plasma membrane. We also show that the carriers are transported from perinuclear recycling endosomes to the cell periphery along microtubules. Total internal reflection fluorescence microscopy of cells expressing EGFP-tagged transferrin receptor revealed that Rab11 depletion inhibits tethering and fusion of recycling carriers to the plasma membrane. Depletion of a component of the exocyst tethering complex, Sec15 or Exo70, the former which interacts with Rab11, leads to essentially the same phenotypes as those of Rab11 depletion. Thus, in addition to its role in recycling processes at perinuclear recycling endosomes, Rab11 is transported along microtubules to the cell periphery through association with recycling carriers, and directly regulates vesicle exocytosis at the plasma membrane in concert with the exocyst.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

APPL1 regulates basal NF-{kappa}B activity by stabilizing NIK

Advance Online Publication June 8, 2012 doi: 10.1242/?jcs.105171 APPL1 is a multifunctional adaptor protein that binds membrane receptors, signaling proteins and nuclear factors, thereby acting in endosomal trafficking and in different signaling pathways. Here we uncover a novel role of APPL1 as a positive regulator of transcriptional activity of NF-?B under basal but not TNFa-stimulated conditions. APPL1 was found to directly interact with TRAF2, an adaptor protein known to activate the canonical NF-?B signaling. APPL1 synergized with TRAF2 to induce NF-?B activation and both proteins were necessary for this process by functioning upstream of the IKK complex. Although TRAF2 was not detectable on APPL endosomes, endosomal recruitment of APPL1 was required for its function in the NF-?B pathway. Importantly, in the canonical pathway APPL1 appeared to regulate the proper spatial distribution of p65 in the absence of cytokine stimulation, since its overexpression enhanced and its depletion reduced the nuclear accumulation of p65. Analyzing the patterns of gene transcription upon APPL1 overproduction or depletion we found altered expression of NF-?B target genes encoding cytokines. At the molecular level, overexpressed APPL1 markedly increased the level of NIK, the key component of the noncanonical NF-?B pathway, by reducing its association with the degradative complex containing TRAF2, TRAF3 and cIAP1. In turn, high levels of NIK triggered nuclear translocation of p65. Collectively, we propose that APPL1 regulates basal NF-?B activity by modulating the stability of NIK, which affects the activation of p65. This places APPL1 as a novel link between the canonical and noncanonical machineries of NF-?B activation.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Share Alike License, which permits unrestricted non-commercial use, distribution and reproduction in any medium provided that the original work is properly cited and all further distributions of the work or adaptation are subject to the same Creative Commons License terms.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.