• Absorption spectra of radical ions of polyenones of biological interest.

      Land, Edward J; Lafferty, Joseph; Sinclair, Roy S; Truscott, T George; Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester (1978)
    • AC133+ G0 cells from cord blood show a high incidence of long-term culture-initiating cells and a capacity for more than 100 million-fold amplification of colony-forming cells in vitro.

      Summers, Yvonne J; Heyworth, Clare M; De Wynter, Erika A; Hart, Claire A; Chang, James; Testa, Nydia G; Cancer Research UK Department of Experimental Haematology, Paterson Institute for Cancer Research, Manchester. yvonnejsummers@aol.com (2004)
      AC133+ cells may provide an alternative to CD34+ cells as a target for cell expansion and gene therapy protocols. We examined the differences in proliferative potential between cord blood selected for AC133 or CD34 in serum-free, stroma cell-free culture for up to 30 weeks. Because most hemopoietic stem cells reside within the G0/G1 phase of the cell cycle, we combined enrichment according to AC133 or CD34 expression with G0 position in the cell cycle to identify populations enriched for putative stem cells. Our results show that AC133+ G0 cells demonstrated a long-term culture-initiating cell incidence of 1 in 4.2 cells, had a colony-forming cell incidence of 1 in 2.8 cells, were capable of producing 660 million-fold expansion of nucleated cells and 120 million-fold expansion of colony-forming units-granulocyte-macrophage over a period of 30 weeks, and were consistently superior to CD34+ G0 cells according to these parameters. Furthermore, we have shown that AC133+CD34- cells have the ability to generate CD34+ cells in culture, which suggests that at least some AC133+ cells are ancestral to CD34+ cells. We conclude that AC133 isolation provides a better means of selection for primitive hemopoietic cells than CD34 and that, in combination with isolation according to G0 phase of the cell cycle, AC133 isolation identifies a highly enriched population of putative stem cells.
    • Accelerated list-mode EM algorithm

      Reader, Andrew J; Manavaki, Roido; Zhao, Sha; Julyan, Peter J; Hastings, David L; Zweit, Jamal; Department of Instrumentation and Analytical Science, University of Manchester (2002)
    • Accelerated repopulation of intestine post-irradiation following intraluminal injection of a mucosal cell suspension or its supernatant.

      Chomiczewski, K; Hendry, Jolyon H; Potten, Christopher S; Cancer Research Campaign Department of Experimental Radiation Oncology, Christie Hospital (NHS) Trust, Manchester, UK. (1993-01)
      The injection of (1-7) x 10(5) mucosal cells into the intestinal lumen at 4 h after 14 or 18 Gy increased the number of intestinal microcolonies (> or = 10 cell foci) and microclusters (4-9 cell foci) when assayed at day 3. The effects were less when (a) the interval between irradiation and injection was increased to 20 h, (b) the assay time was increased to 4 days or more, (c) a cell supernatant was injected instead. The data indicate that the injections stimulated earlier regeneration. The effect of the supernatant suggests that the stimulation is mediated through a humoral factor.
    • Accelerated telomere shortening following allogeneic transplantation is independent of the cell source and occurs within the first year post transplant.

      Robertson, J D; Testa, Nydia G; Russell, N H; Jackson, G; Parker, A N; Milligan, D W; Stainer, C; Chakrabarti, S; Dougal, Mark; Chopra, Rajesh; et al. (2001-06)
      Telomere shortening has been documented in the blood cells of recipients of allogeneic bone marrow transplants compared with their donors. Allogeneic peripheral blood progenitor cells (PBPCs) have been increasingly used as an alternative to bone marrow. Their advantages include earlier engraftment and immune reconstitution following transplantation. We have measured telomere length of neutrophils and T cells in fully engrafted recipients of allogeneic bone marrow (n = 19) and allogeneic PBPC (n = 17) and also measured sequential telomere length in four patients after transplantation. Overall, significant telomere shortening occurred in recipients in neutrophils (0.3 kb, P < 0.001) and T cells (0.2 kb, P = 0.045). The data demonstrate that first, the degree of shortening was the same for BM and PBPC transplants and was not related to the time taken to engraft neutrophils and platelets and second, telomere shortening occurs in the first year post transplant without further shortening during the period of observation. These data suggest that the superiority of engraftment seen in PBPC transplants is independent of telomere shortening and other mechanisms such as homing or seeding may be more important.
    • Accelerated telomere shortening in young recipients of allogeneic bone-marrow transplants.

      Wynn, Robert F; Cross, Michael A; Hatton, C; Will, A M; Lashford, Linda S; Dexter, T Michael; Testa, Nydia G; Cancer Research Campaign Department of Experimental Haematology, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK. (1998-01-17)
      BACKGROUND: The establishment of donor-derived haemopoiesis in the recipients of allogeneic bone-marrow transplants (BMT) involves extensive proliferation of haemopoietic stem cells. The biological consequences of this replicative stress are ill defined, but any "ageing" effect would carry the risk of an increased frequency of clonal disorders during later life. We compared blood-cell mean telomere lengths in donor/recipient pairs. METHODS: Mean telomere length was calculated by in-gel hybridisation to leucocyte DNA from 56 normal individuals aged 0-96 years, and from 14 consecutive BMT recipients (aged 2-14 years) plus their respective donors (aged 2-46 years). Engraftment was confirmed by variable numbers of tandem repeats (VNTR) or gender analysis. FINDINGS: On average, blood-cell telomeres of transplant recipients were 0.4 kb (95% CI -0.2 to -0.6) shorter than those of their respective donors. This degree of telomere loss is equivalent to a median of 15 years' (range 0-40) ageing in the healthy controls. INTERPRETATION: The kinetics of haemopoietic engraftment impose replicative stress on the haemopoietic stem cells, resulting in a pronounced ageing effect, which may be sufficient to accelerate the onset of clonal haemopoietic disorders usually associated with later life. Monitoring of haemopoietic status in BMT recipients as time since BMT increases will be important. Assessment of transplant protocols under development in terms of their effects on telomere shortening is also indicated.
    • Accessibility of chromatin to DNA polymerase I and location of the F1 histone.

      Saffhill, Roy; Itzhaki, Ruth F; Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester (1975-01)
      The effect of prebound poly-L-lysine upon the template activity of DNA, chromatin and F1 histone-depleted chromatin for E. coli DNA polymerase I has been investigated. Measurements have been made in the absence and presence of 0.1M NaCl. From the results we conclude that only ca 60% of the polylysine-accessible DNA, i.e. 22% of the total DNA of the chromatin, is accessible to the DNA polymerase I and that ca. 30% of the polylysine-accessible DNA, i.e. 11% of the total DNA, is associated with the F1 histone.
    • Accessible DNA in chromatin

      Itzhaki, Ruth F; Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester M20 9BX (1974)
    • Accessing nuclear structure for field emission, in lens, scanning electron microscopy (FEISEM).

      Allen, Terence D; Bennion, G R; Rutherford, Sandra A; Reipert, Siegfried; Ramalho, A; Kiseleva, Elena; Goldberg, Martin W; CRC Department of Structural Cell Biology, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK. ulttda@picr.cr.man.ac.uk (1996)
      Scanning electron microscopy (SEM) has had a shorter time course in biology than conventional transmission electron microscopy (TEM) but has nevertheless produced a wealth of images that have significantly complemented our perception of biological structure and function from TEM information. By its nature, SEM is a surface imaging technology, and its impact at the subcellular level has been restricted by the considerably reduced resolution in conventional SEM in comparison to TEM. This restriction has been removed by the recent advent of high-brightness sources used in lensfield emission instruments (FEISEM) which have produced resolution of around 1 nanometre, which is not usually a limiting figure for biological material. This communication reviews our findings in the use of FEISEM in the imaging of nuclear surfaces, then associated structures, such as nuclear pore complexes, and the relationships of these structures with cytoplasmic and nucleoplasmic elements. High resolution SEM allows the structurally orientated cell biologist to visualise, directly and in three dimensions, subcellular structure and its modulation with a view to understanding, its functional significance. Clearly, intracellular surfaces require separation from surrounding structural elements in vivo to allow surface imaging, and we review a combination of biochemical and mechanical isolation methods for nuclear surfaces.
    • Accumulation of p53 in relation to long-term prognosis in colorectal carcinoma.

      Starzynska, T; Bromley, Michael; Marlicz, K; Roberts, Stephen A; Ucinski, M; Stern, Peter L; Department of Gastroenterology Medical Pomeranian Academy, Unii Lubelskiej, Poland. (1997-02)
      OBJECTIVE: To evaluate the prognostic value of p53 in colorectal cancer. DESIGN: A retrospective study to investigate the correlation between p53 in tumour tissue and the course of patients' disease. PATIENTS: One hundred and two patients who underwent radical surgery for colorectal cancer and were followed up for a minimum of 5 years, or until death, were included in this study. METHODS: The p53 expression in tumour tissue was studied by immunohistochemistry using CM1 polyclonal rabbit antibody and formalin-fixed, paraffin-embedded material. RESULTS: p53 accumulation was detected in 46% (47/102) of the tumours. There was no significant difference in long-term survival between the patients with p53 positive and negative tumours (P=0.86). Five-year survival rates were 55% for p53 positive tumours compared with 56% for patients with p53 negative tumours. However, patients with p53 overexpressing tumours showed a higher local recurrence rate than those having carcinomas with undetectable levels of p53, 23% versus 9% respectively; the 2-year actuarial rates of 26% and 9% were statistically different (P=0.015). CONCLUSION: The results suggest that in colorectal carcinoma accumulation of p53 is not associated with a difference in long-term prognosis. However, this phenomenon might be useful in the identification of patients with a high risk of local recurrence.
    • Accuracy of telomerase in cervical lesions: a systematic review.

      Rosa, M I; Medeiros, Lidia Rosi; Bozzetti, M C; Fachel, J; Wendland, E; Zanini, R R; Moraes, A B; Rosa, Daniela D; Postgraduate Program in Epidemiology, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, Brazil. mir@unesc.net (2007)
      The detection of telomerase activity in cervix may provide information on cervical carcinogenesis and may be a marker to monitor cervical intraepithelial neoplasia transition. A quantitative systematic review was performed to estimate the accuracy of telomerase assay in cervical lesions. Studies that evaluated the telomerase test (telomerase repeated amplification protocol) for the diagnosis of cervix lesions and compared it to paraffin-embedded sections as the diagnostic standard were included. Ten studies were analyzed, which included 1069 women. The diagnostic odds ratio (DOR) for a positive telomerase test for low-grade squamous intraepithelial lesions (Lo-SIL) vs normal or benign lesions was 3.2 (95% CI, 1.9-5.6). The DOR for a positive telomerase test for high-grade squamous intraepithelial lesions (Hi-SIL) vs Lo-SIL, normal or benign lesions was 5.8 (95% CI, 3.1-10). For cervix cancer vs Hi-SIL, the DOR for a positive telomerase test was 8.1 (95% CI, 3.2-20.3) and for cervix cancer vs Lo-SIL, normal or benign lesions, it was 40.9 (95% CI, 18.2-91). Our data support the current hypothesis that telomerase may activate an early event in cervical carcinogenesis that could be associated with the initiation and progression of cervical lesions.
    • Accurate and sensitive quantitation of N7-methyldeoxyguanosine-3'-monophosphate by 32P-postlabeling and storage-phosphor imaging.

      Haque, Kemal; Cooper, Donald P; Van Delft, J H; Lee, Siow Ming; Povey, Andrew C; Cancer Research Campaign Department of Carcinogenesis and Medical Oncology, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, U.K. (1997-06)
      As N7-methyldeoxyguanosine-3'-monophosphate (N7-MedGp) is the major, persistent DNA lesion generated by methylating agents, a combined HPLC/32P-postlabeling assay has been developed to quantitate this adduct in human DNA. N7-MedGp was purified from normal nucleotides by anion-exchange chromatography followed by reverse-phase HPLC procedures. The adduct was then 32P-postlabeled and resolved by two-dimensional TLC for detection and quantitation by storage-phosphor imaging. The effect of conditions used for DNA purification and digestion on the recovery of N7-MedGp has been investigated. Extended, raised temperature incubations normally employed during DNA purification were demonstrated to result in considerable loss of adduct through depurination after 22 h at 65 and 37 degrees C (82% and 20% loss, respectively), but depurination was reduced to 5% if the incubation was performed at either 4 or 22 degrees C. Similarly, close to optical recovery (83%) of N7-MedGp was achieved after DNA digestion by incubating at 4 degrees C, pH 7.4, for 18 h in the presence of micrococcal nuclease and calf spleen phosphodiesterase from Sigma and Boehringer Mannheim, respectively. Overall, the recovery of N7-MedGp was 40%, resulting in a detection limit of 1.3 fmol which is equivalent to 0.16 mumol of adduct/mol of 2'-deoxyguanosine-3'-monophosphate (dGp) when analyzing 10 micrograms of DNA. The N7-MedGp content of DNA that had been methylated in vitro using 0, 16, and 80 microM N-methyl-N-nitrosourea (NMU) was determined by 32P-postlabeling to be 12, 112, and 671 mumol of N7-MedGp/mol of dGp. Electrochemical detection of N7-methylguanine (N7-MeG) after HPLC purification measured approximately 2-fold higher levels, i.e., 25, 225, and 1080 mumol of N7-MeG/mol of Gua, at each NMU concentration, respectively. The levels of N7-MedGp in the white blood cell (WBC) DNA of patients receiving a single dose of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) chemotherapy were determined by 32P-postlabeling. Maximum levels were found 4-6 h after treatment, and in two out of four individuals adduct levels were decreased by 21 h. Prior to treatment, N7-MedGp was detectable in WBC DNA in two out of the four individuals indicating that nontherapeutic exposure to methylating agents had occurred.
    • An accurate method to quantify breathing-induced prostate motion for patients implanted with electromagnetic transponders.

      Giandini, T; Panaino, Costanza M V; Avuzzi, B; Morlino, S; Villa, S; Bedini, N; Carabelli, G; Frasca, S; Romanyukha, A; Rosenfeld, A; et al. (2017-02-11)
      To validate and apply a method for the quantification of breathing-induced prostate motion (BIPM) for patients treated with radiotherapy and implanted with electromagnetic transponders for prostate localization and tracking.
    • Accurate MR image registration to anatomical reference space for diffuse glioma

      Visser, M; Petr, J; Muller, DMJ; Eijgelaar, RS; Hendriks, EJ; Witte, M; Barkhof, F; van Herk, Marcel; Mutsaerts, H; Vrenken, H; et al. (2020)
      To summarize the distribution of glioma location within a patient population, registration of individual MR images to anatomical reference space is required. In this study, we quantified the accuracy of MR image registration to anatomical reference space with linear and non-linear transformations using estimated tumor targets of glioblastoma and lower-grade glioma, and anatomical landmarks at pre- and post-operative time-points using six commonly used registration packages (FSL, SPM5, DARTEL, ANTs, Elastix, and NiftyReg). Routine clinical pre- and post-operative, post-contrast T1-weighted images of 20 patients with glioblastoma and 20 with lower-grade glioma were collected. The 2009a Montreal Neurological Institute brain template was used as anatomical reference space. Tumors were manually segmented in the patient space and corresponding healthy tissue was delineated as a target volume in the anatomical reference space. Accuracy of the tumor alignment was quantified using the Dice score and the Hausdorff distance. To measure the accuracy of general brain alignment, anatomical landmarks were placed in patient and in anatomical reference space, and the landmark distance after registration was quantified. Lower-grade gliomas were registered more accurately than glioblastoma. Registration accuracy for pre- and post-operative MR images did not differ. SPM5 and DARTEL registered tumors most accurate, and FSL least accurate. Non-linear transformations resulted in more accurate general brain alignment than linear transformations, but tumor alignment was similar between linear and non-linear transformation. We conclude that linear transformation suffices to summarize glioma locations in anatomical reference space. Keywords: computer-assisted; glioma; image processing; linear registration; magnetic resonance imaging; non-linear registration.
    • Acetylation-dependent oncogenic activity of metastasis-associated protein 1 co-regulator.

      Ohshiro, Kazufumi; Rayala, Suresh K; Wigerup, Caroline; Pakala, Suresh B; Natha, Reddy S Divijendra; Gururaj, Anupama E; Molli, Poonam R; Månsson, Sofie Svensson; Ramezani, Ali; Hawley, Robert G; et al. (2010-09)
      High expression of metastasis-associated protein 1 co-regulator (MTA1), a component of the nuclear remodelling and histone deacetylase complex, has been associated with human tumours. However, the precise role of MTA1 in tumorigenesis remains unknown. In this study, we show that induced levels of MTA1 are sufficient to transform Rat1 fibroblasts and that the transforming potential of MTA1 is dependent on its acetylation at Lys626. Underlying mechanisms of MTA1-mediated transformation include activation of the Ras-Raf pathway by MTA1 but not by acetylation-inactive MTA1; this was due to the repression of Galphai2 transcription, which negatively influences Ras activation. We observed that acetylated MTA1-histone deacetylase (HDAC) interaction was required for the recruitment of the MTA1-HDAC complex to the Galphai2 regulatory element and consequently for the repression of Galphai2 transcription and expression leading to activation of the Ras-Raf pathway. The findings presented in this study provide for the first time--to the best of our knowledge--evidence of acetylation-dependent oncogenic activity of a cancer-relevant gene product.
    • Acidic phospholipid species inhibit adenylate cyclase activity in rat liver plasma membranes.

      Houslay, M; Needham, L; Dodd, Nicholas J F; Grey, A; Molecular Pharmacology Group, Institute of Biochemistry, University of Glasgow, Glasgow G12 8QQ, Scotland U.K. (1986-04-01)
      Incubation of rat liver plasma membranes with liposomes of dioleoyl phosphatidic acid (dioleoyl-PA) led to an inhibition of adenylate cyclase activity which was more pronounced when fluoride-stimulated activity was followed than when glucagon-stimulated activity was followed. If Mn2+ (5 mM) replaced low (5 mM) [Mg2+] in adenylate cyclase assays, or if high (20 mM) [Mg2+] were employed, then the perceived inhibitory effect of phosphatidic acid was markedly reduced when the fluoride-stimulated activity was followed but was enhanced for the glucagon-stimulated activity. The inhibition of adenylate cyclase activity observed correlated with the association of dioleoyl-PA with the plasma membranes. Adenylate cyclase activity in dioleoyl-PA-treated membranes, however, responded differently to changes in [Mg2+] than did the enzyme in native liver plasma membranes. Benzyl alcohol, which increases membrane fluidity, had similar stimulatory effects on the fluoride- and glucagon-stimulated adenylate cyclase activities in both native and dioleoyl-PA-treated membranes. Incubation of the plasma membranes with phosphatidylserine also led to similar inhibitory effects on adenylate cyclase and responses to Mg2+. Arrhenius plots of both glucagon- and fluoride-stimulated adenylate cyclase activity were different in dioleoyl-PA-treated plasma membranes, compared with native membranes, with a new 'break' occurring at around 16 degrees C, indicating that dioleoyl-PA had become incorporated into the bilayer. E.s.r. analysis of dioleoyl-PA-treated plasma membranes with a nitroxide-labelled fatty acid spin probe identified a new lipid phase separation occurring at around 16 degrees C with also a lipid phase separation occurring at around 28 degrees C as in native liver plasma membranes. It is suggested that acidic phospholipids inhibit adenylate cyclase by virtue of a direct headgroup specific interaction and that this perturbation may be centred at the level of regulation of this enzyme by the stimulatory guanine nucleotide regulatory protein NS.
    • Acquired resistance of ER- positive breast cancer to endocrine treatment confers an adaptive sensitivity to TRAIL through post-translational downregulation of c-FLIP.

      Piggott, L; da Silva, A; Robinson, T; Santiago-Gómez, Angélica; Simões, Bruno M; Becker, M; Fichtner, I; Andera, L; Piva, M; Vivanco, M; et al. (2018-01-23)
      One-third of ER-positive breast cancer patients who initially respond to endocrine therapy become resistant to treatment. Such treatment failure is associated with poor prognosis and remains an area of unmet clinical need.  Here we identify a specific post-translational modification that occurs during endocrine resistance and which results in tumour susceptibility to the apoptosis inducer TNF-Related Apoptosis-Inducing Ligand (TRAIL). This potentially offers a novel stratified approach to targeting endocrine resistant breast cancer.
    • Acquired resistance to cancer immunotherapy: role of tumor-mediated immunosuppression

      Saleh, R; Elkord, Eyad; Cancer Research Center, Qatar Biomedical Research Institute (QBRI), Hamad Bin Khalifa University (HBKU), Qatar Foundation (QF), PO Box 34110, Doha, Qatar (2019)
      In the tumor microenvironment (TME), tumor cells are constantly evolving to reduce neoantigen generation and the mutational burden to escape the anti-tumor response. This will lower tumor reactivity to the adaptive immune response and give rise to tumor intrinsic factors, such as altered expression of immune regulatory molecules on tumor cells. Tumor-extrinsic factors, such as immunosuppressive cells, soluble suppressive molecules or inhibitory receptors expressed by immune cells will alter the composition and activity of tumor-infiltrating lymphocytes (TILs) (by increasing T regulatory cells:T effector cells ratio and inhibiting T effector cell function) and promote tumor growth and metastasis. Together, these factors limit the response rates and clinical outcomes to a particular cancer therapy. Within the TME, the cross-talks between immune and non-immune cells result in the generation of positive feedback loops, which augment immunosuppression and support tumor growth and survival (termed as tumor-mediated immunosuppression). Cancer immunotherapies, such as immune checkpoint inhibitors (ICIs) and adoptive cell transfer (ACT), have shown therapeutic efficacy in hematologic cancers and different types of solid tumors. However, achieving durable response rates in some cancer patients remains a challenge as a result of acquired resistance and tumor immune evasion. This could be driven by the cellular and molecular suppressive network within the TME or due to the loss of tumor antigens. In this review, we describe the contribution of the immunosuppressive cellular and molecular tumor network to the development of acquired resistance against cancer immunotherapies. We also discuss potential combined therapeutic strategies which could help to overcome such resistance against cancer immunotherapies, and to enhance anti-tumor immune responses and improve clinical outcomes in patients.
    • Acquired resistance to fractionated radiotherapy can be overcome by concurrent PD-L1 blockade.

      Dovedi, Simon J; Adlard, A; Lipowska-Bhalla, Grazyna; McKenna, Conor; Jones, Sherrie; Cheadle, Eleanor J; Stratford, I; Poon, E; Morrow, M; Stewart, R; et al. (2014-10-01)
      Radiotherapy is a major part in the treatment of most common cancers, but many patients experience local recurrence with metastatic disease. In evaluating response biomarkers, we found that low doses of fractionated radiotherapy led to PD-L1 upregulation on tumor cells in a variety of syngeneic mouse models of cancer. Notably, fractionated radiotherapy delivered in combination with αPD-1 or αPD-L1 mAbs generated efficacious CD8(+) T-cell responses that improved local tumor control, long-term survival, and protection against tumor rechallenge. These favorable outcomes were associated with induction of a tumor antigen-specific memory immune response. Mechanistic investigations showed that IFNγ produced by CD8(+) T cells was responsible for mediating PD-L1 upregulation on tumor cells after delivery of fractionated radiotherapy. Scheduling of anti-PD-L1 mAb was important for therapeutic outcome, with concomitant but not sequential administration with fractionated radiotherapy required to improve survival. Taken together, our results reveal the mechanistic basis for an adaptive response by tumor cells that mediates resistance to fractionated radiotherapy and its treatment failure. With attention to scheduling, combination immunoradiotherapy with radiotherapy and PD-1/PD-L1 signaling blockade may offer an immediate strategy for clinical evaluation to improve treatment outcomes.
    • Actin- and protein-4.1-containing filaments link nuclear pore complexes to subnuclear organelles in Xenopus oocyte nuclei.

      Kiseleva, Elena; Drummond, Sheona P; Goldberg, Martin W; Rutherford, Sandra A; Allen, Terence D; Wilson, Katherine L; Department of Structural Cell Biology, Paterson Institute for Cancer Research, Christie Hospital, Manchester, M20 9BX, UK. (2004-05-15)
      We imaged the interiors of relatively intact Xenopus oocyte nuclei by field emission scanning electron microscopy (feSEM) and visualized a network of filaments that attach to nuclear pore complexes and extend throughout the nucleus. Within the nucleus, these 'pore-linked filaments' (PLFs) were embedded into spherical structures 100 nm to approximately 5 microm in diameter. A subset of spheres was identified as Cajal bodies by immuno-gold labeling; the rest were inferred to be nucleoli and snurposomes both of which are abundant in Xenopus oocyte nuclei. Most PLFs were independent of chromatin. The thickness of a typical PLF was 40 nm (range, approximately 12-100 nm), including the 4 nm chromium coat. PLFs located inside the nucleus merged, bundled and forked, suggesting architectural adaptability. The PLF network collapsed upon treatment with latrunculin A, which depolymerizes actin filaments. Jasplakinolide, which stabilizes actin filaments, produced PLFs with more open substructure including individual filaments with evenly-spaced rows of radially projecting short filaments. Immuno-gold labeling of untreated oocyte nuclei showed that actin and protein 4.1 each localized on PLFs. Protein 4.1-gold epitopes were spaced at approximately 120 nm intervals along filaments, and were often paired ( approximately 70 nm apart) at filament junctions. We suggest that protein 4.1 and actin contribute to the structure of a network of heterogeneous filaments that link nuclear pore complexes to subnuclear organelles, and discuss possible functions for PLFs in nuclear assembly and intranuclear traffic.