1
|
Walen KH. Haploidization of Human Diploid Metaphase Cells: Is This Genome Reductive Mechanism Opperational in Near-Haploid Leukemia? ACTA ACUST UNITED AC 2014. [DOI: 10.4236/jct.2014.51013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
2
|
Walen KH. Neoplastic-Like CELL Changes of Normal Fibroblast Cells Associated with Evolutionary Conserved Maternal and Paternal Genomic Autonomous Behavior (Gonomery). ACTA ACUST UNITED AC 2014. [DOI: 10.4236/jct.2014.59094] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
3
|
Buch C, Lindberg R, Figueroa R, Gudise S, Onischenko E, Hallberg E. An integral protein of the inner nuclear membrane localizes to the mitotic spindle in mammalian cells. J Cell Sci 2009; 122:2100-7. [DOI: 10.1242/jcs.047373] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Here, we characterize a transmembrane protein of the nuclear envelope that we name spindle-associated membrane protein 1 (Samp1). The protein is conserved in metazoa and fission yeast and is homologous to Net5 in rat and Ima1 in Schizosaccharomyces pombe. We show that, in human cells, the protein is a membrane-spanning polypeptide with an apparent molecular mass of 43 kDa. This is consistent with a predicted polypeptide of 392 amino acids that has five transmembrane segments and its C-terminus exposed to the nucleoplasm. During interphase, Samp1 was specifically distributed in the inner nuclear membrane. Post-transcriptional silencing of Samp1 expression resulted in separation of centrosomes from the nuclear envelope, indicating that it is functionally connected to the cytoskeleton. At the onset of mitosis, most of the protein dispersed out into the ER, as expected. However, during mitosis, a significant fraction of the protein specifically localized to the polar regions of the mitotic spindle. We demonstrate for the first time, in human cells, the existence of a membranous structure overlapping with the mitotic spindle. Interestingly, another integral inner nuclear membrane protein, emerin, was absent from the spindle-associated membranes. Thus, Samp1 defines a specific membrane domain associated with the mitotic spindle.
Collapse
Affiliation(s)
- Charlotta Buch
- Department of Biosciences and Nutrition, Karolinska Institute, SE-141 57 Huddinge, Sweden
- Life Sciences, Södertörns University, SE-141 89 Huddinge, Sweden
| | - Robert Lindberg
- Life Sciences, Södertörns University, SE-141 89 Huddinge, Sweden
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Ricardo Figueroa
- Life Sciences, Södertörns University, SE-141 89 Huddinge, Sweden
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Santhosh Gudise
- Department of Biosciences and Nutrition, Karolinska Institute, SE-141 57 Huddinge, Sweden
- Life Sciences, Södertörns University, SE-141 89 Huddinge, Sweden
| | - Evgeny Onischenko
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
| | - Einar Hallberg
- Life Sciences, Södertörns University, SE-141 89 Huddinge, Sweden
| |
Collapse
|
4
|
Pickett-Heaps J, Forer A. Mitosis: spindle evolution and the matrix model. PROTOPLASMA 2009; 235:91-99. [PMID: 19255823 DOI: 10.1007/s00709-009-0030-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 01/07/2009] [Indexed: 05/27/2023]
Abstract
Current spindle models explain "anaphase A" (movement of chromosomes to the poles) in terms of a motility system based solely on microtubules (MTs) and that functions in a manner unique to mitosis. We find both these propositions unlikely. An evolutionary perspective suggests that when the spindle evolved, it should have come to share not only components (e.g., microtubules) of the interphase cell but also the primitive motility systems available, including those using actin and myosin. Other systems also came to be involved in the additional types of motility that now accompany mitosis in extant spindles. The resultant functional redundancy built reliability into this critical and complex process. Such multiple mechanisms are also confusing to those who seek to understand how chromosomes move. Narrowing this commentary down to just anaphase A, we argue that the spindle matrix participates with MTs in anaphase A and that this matrix may contain actin and myosin. The diatom spindle illustrates how such a system could function. This matrix may be motile and work in association with the MT cytoskeleton, as it does with the actin cytoskeleton during cell ruffling and amoeboid movement. Instead of pulling the chromosome polewards, the kinetochore fibre's role might be to slow polewards movement to allow correct chromosome attachment to the spindle. Perhaps the earliest eukaryotic cell was a cytoplast organised around a radial MT cytoskeleton. For cell division, it separated into two cytoplasts via a spindle of overlapping MTs. Cytokinesis was actin-based cleavage. As chromosomes evolved into individual entities, their interaction with the dividing cytoplast developed into attachment of the kinetochore to radial (cytoplast) MTs. We believe it most likely that cytoplasmic motility systems participated in these events.
Collapse
|
5
|
Abstract
Recent in vitro and in vivo studies of the proteins responsible for the active partitioning of bacterial plasmids suggest that it will be possible to develop a quantitative, molecular understanding of this form of DNA segregation.
Collapse
Affiliation(s)
- Daniel J Needleman
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
| |
Collapse
|
6
|
Abstract
The GTPase Ran has a key role in nuclear import and export, mitotic spindle assembly and nuclear envelope formation. The cycling of Ran between its GTP- and GDP-bound forms is catalyzed by the chromatin-bound guanine nucleotide exchange factor RCC1 and the cytoplasmic Ran GTPase-activating protein RanGAP. The result is an intracellular concentration gradient of RanGTP that equips eukaryotic cells with a ;genome-positioning system' (GPS). The binding of RanGTP to nuclear transport receptors (NTRs) of the importin beta superfamily mediates the effects of the gradient and generates further downstream gradients, which have been elucidated by fluorescence resonance energy transfer (FRET) imaging and computational modeling. The Ran-dependent GPS spatially directs many functions required for genome segregation by the mitotic spindle during mitosis. Through exportin 1, RanGTP recruits essential centrosome and kinetochore components, whereas the RanGTP-induced release of spindle assembly factors (SAFs) from importins activates SAFs to nucleate, bind and organize nascent spindle microtubules. Although a considerable fraction of cytoplasmic SAFs is active and RanGTP induces only partial further activation near chromatin, bipolar spindle assembly is robustly induced by cooperativity and positive-feedback mechanisms within the network of Ran-activated SAFs. The RanGTP gradient is conserved, although its roles vary among different cell types and species, and much remains to be learned regarding its functions.
Collapse
Affiliation(s)
- Petr Kalab
- Laboratory of Cell and Molecular Biology, National Cancer Institute, Bethesda, MD 20892-4256, USA.
| | | |
Collapse
|