Education in Microscopy and Digital Imaging

Microtubule-associated protein 4 (MAP4) promotes MT assembly in vitro and is localized along MTs in vivo. Though this may seem to suggest that MAP4 is the major MAP in nonneuronal cells and that MAP4's normal functions may include the stabilization of MTs in situ, it has been experimentally proven that the association of MAP4 with MTs is not necessary for MT assembly or for the MT-based functions in cultured cells. A considerable role for MAP4 is not excluded by these results, however, as MAP4 could be a constituent of a functionally redundant system. The intracellular microtubule network and the cell nucleus are clearly visible in this digital video sequence due to fluorescent labeling of cultured human osteosarcoma cells (U-2 line) with mEmerald fused to MAP4 and mCherry fused to H2B.

Microtubules were fluorescently tagged with mEmerald fused to MAP4, a microtubule-associated protein. mEmerald is a green fluorescent variant of EGFP with improved brightness and photostability. Excitation of mEmerald peaks at 487 nanometers and emission peaks at 509 nanometers. The red fluorescent protein employed to tag histone H2B, mCherry, was developed through directed mutagenesis of mRFP1, a monomeric DsRed mutant. Peak excitation and emission of mCherry occur at 587 and 610 nanometers, respectively.