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A widely distributed nuclear protein immunologically related to the microtubule-associated protein MAP1 is associated
Abstract:
A 280-kDa protein (p280) confined to the nucleus of interphase cells becomes associated with the mitotic spindle during cell division. p280 is immunologically related to the microtubule-associated protein MAP1, as shown by cross-reactivity with monoclonal (8D12) and polyclonal antibodies raised against MAP1. However, p280 is distinct from MAP1 as judged by its lower molecular size, proteolytic degradation products, presence in preparations of purified nuclei from which MAP1 is absent, and absence from the cytosol fraction that contains MAP1. Immunofluorescence microscopy of cells in interphase using 8D12 reveals punctate staining of the nucleus, cytoplasmic microtubules, and the microtubule organizing center. Dividing cells display strong staining of the spindle, centrioles, and mid-body. The only exception to this staining pattern is marsupial Pt k2 cells that contain p280 in the nucleus and lack MAP1. These cells exhibit fluorescent staining of the nucleus and the microtubule organizing center when in interphase, of spindle and centrioles in mitosis, and show no staining of cytoplasmic and mid-body microtubules.
Insights
A novel nuclear protein, p280, associates with the mitotic spindle during cell division and is related to microtubule-associated protein MAP1. Despite similarities, p280 is distinct from MAP1, showing unique cellular localization and properties.
Area of Science:
- Cell Biology
- Molecular Biology
- Cytoskeletal Dynamics
Background:
- Microtubule-associated proteins (MAPs) are crucial for microtubule organization and function.
- MAP1 is a well-characterized MAP involved in microtubule stabilization and assembly.
- The cellular localization and distinct functions of MAPs are critical for understanding cell division and interphase organization.
Purpose of the Study:
- To characterize a novel 280-kDa protein (p280) identified in cell nuclei.
- To investigate the relationship between p280 and microtubule-associated protein MAP1.
- To determine the subcellular localization and dynamic behavior of p280 during the cell cycle.
Main Methods:
- Immunological assays using monoclonal (8D12) and polyclonal antibodies against MAP1.
- Western blotting to assess molecular size and degradation products.
- Subcellular fractionation to isolate nuclear and cytosolic components.
- Immunofluorescence microscopy to visualize protein localization in interphase and dividing cells.
Main Results:
- p280 is a 280-kDa protein primarily localized to the nucleus in interphase cells.
- p280 associates with the mitotic spindle during cell division.
- p280 shows immunological cross-reactivity with MAP1 but is distinct in size, degradation, and subcellular distribution.
- Immunofluorescence reveals p280 in the nucleus, cytoplasmic microtubules, and microtubule organizing center in interphase cells, and on the spindle, centrioles, and mid-body during mitosis.
- Marsupial Pt k2 cells lacking MAP1 exhibit p280 in the nucleus and at the microtubule organizing center, but not on cytoplasmic or mid-body microtubules.
Conclusions:
- p280 is a novel nuclear protein functionally and structurally related to MAP1 but with distinct characteristics.
- p280 plays a role in both interphase nuclear organization and mitotic spindle function.
- The differential localization of p280 and MAP1 suggests distinct roles in microtubule dynamics and cellular architecture.