part of the spindle matrix in mitosis. Indeed, the yeast nuclear protein FIN1p contains coiledcoil domains and associates with spindles during mitosis (46). Furthermore, purified FIN1p selfassembles into 10-nm filaments resembling the cytoskeletal intermediate filaments formed in vitro (46).In interphase nuclei of vertebrate cells, LB is concentrated at the nuclear lamina and is also distributed throughout the nucleoplasm. During interphase, the lamins interact with a wide range of nuclear proteins to regulate many nuclear functions as well as nuclear structural integrity. At the onset of mitosis, lamins are phosphorylated by Cdk1, which leads to the disassembly of nuclear lamina (48,49). The prevailing idea is that the disassembled LB is dispersed throughout the cytoplasm during mitosis. However, a fraction of LB is associated with the mitotic spindle and/or mitotic chromosomes (19,(26)(27)(28). Our studies suggest that LB might perform functions analogous to those of the nuclear lamina to regulate spindle integrity and chromosome organization in mitosis.
Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.
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