1. Working models of perinuclear microtubule nucleation in late G2: hypothesis of a nucleo-cytoplasmic continuum.
Nucleoporins (Nups) are linked to nuclear membrane proteins, forming a continuum between the inner plamina (filamentous proteins that mimic the lamin lattice
and functions in plants) and the outer MT nucleation complexes. Mitotic checkpoint proteins (MAD and BUB complexes) are often linked to chromocentres
and nuclear pores, and may be involved in the continuum organization during interphase. Left, c–TuRC-dependent MT nucleation: GIPs and NEDD1 are additional
assembly factors that are putatively required for MT nucleation. The Augmin complex was observed at the nuclear envelope in interphase. Right, histone
H1-dependent MT nucleation: H1 complexes located close to nuclear pores may lead to assembly of tubulin dimers, pushing the MTs away from the
nucleation site.
‘–’ and ‘+’ indicate intrinsic MT polarity. Black stars indicate unknown proteins involved in anchoring of the nucleation complex at the outer nuclear membrane.
Among regulatory enzymes, the Ran GTPase and Aurora kinases are linked to MT nucleation. Among MT-associated proteins (MAPs), TPX2 is exported from
the nucleoplasm and participates in MT nucleation