Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding

In metaphase chromosomes, chromatin is compacted to a concentration of several hundred mg/ml by mechanisms which remain elusive. Effects mediated by the ionic environment are considered most frequently because mono- and di-valent cations cause polynucleosome chains to form compact ∼30-nm diameter fibres in vitro, but this conformation is not detected in chromosomes in situ. A further unconsidered factor is predicted to influence the compaction of chromosomes, namely the forces which arise from crowding by macromolecules in the surrounding cytoplasm whose measured concentration is 100–200 mg/ml. To mimic these conditions, chromosomes were released from mitotic CHO cells in solutions containing an inert volume-occupying macromolecule (8 kDa polyethylene glycol, 10.5 kDa dextran, or 70 kDa Ficoll) in 100 µM K-Hepes buffer, with contaminating cations at only low micromolar concentrations. Optical and electron microscopy showed that these chromosomes conserved their characteristic structure and compaction, and their volume varied inversely with the concentration of a crowding macromolecule. They showed a canonical nucleosomal structure and contained the characteristic proteins topoisomerase IIα and the condensin subunit SMC2. These observations, together with evidence that the cytoplasm is crowded in vivo, suggest that macromolecular crowding effects should be considered a significant and perhaps major factor in compacting chromosomes. This model may explain why ∼30-nm fibres characteristic of cation-mediated compaction are not seen in chromosomes in situ. Considering that crowding by cytoplasmic macromolecules maintains the compaction of bacterial chromosomes and has been proposed to form the liquid crystalline chromosomes of dinoflagellates, a crowded environment may be an essential characteristic of all genomes

Extremity Soft Tissue Sarcoma in Adults

When treating soft tissue sarcomas (STSs) of the extremities, the major therapeutic goals are survival, local tumor control, optimal function, and minimal morbidity. Surgical resection of the primary tumor is the essential component of treatment for virtually all patients. A wide surgical margin is necessary for local tumor control when surgery is used without radiation, i.e., the cut should traverse normal tissue outside the reactive tumor zone. This is because sarcomas tend to infiltrate normal tissue adjacent to the evident lesion. Thus, removal of the gross lesion by a simple excision alone (only a narrow margin) is followed by relatively high rates of local recurrence. Radical resections are associated with a reduction in the local recurrence rate, but they may compromise limb function. The combination of function-sparing surgery and radiation achieves better rates of local control than either treatment alone, for nearly all patients with STSs, although combined treatment can be associated with acute wound complications in some patients and late normal tissue complications in others. Because both surgical and radiation techniques are both critically important for optimizing local control of tumor and functional outcome, it is important to manage these patients in dedicated multispecialty clinics comprised of physicians with expertise in sarcomas, including orthopedic and general oncology surgeons, radiation oncologists, medical oncologists, sarcoma pathologists, and bone and soft tissue diagnostic radiologists. Radiation therapy can be given by external beam radiation (EBRT) or brachytherapy or combination thereof. EBRT can be given either pre-operatively or post-operatively