Interplay Between Spindle Architecture and Function - International Review of Cell and Molecular Biology - page 110

A

Meiosis II egg

X. tropicalis

X. laevis

Δ p60 Katanin

Δ p60 Katanin

B

Mitosis embryo

X. laevis stage 3 X. laevis stage 8

Cell surface area : volume
increases

~ 4000 cells

4 cells

α
partitions to
membrane

Importin

Importin α

Kif2a - MT destabilizer

Figure 3.7 Microtubule destabilization regulates spindle size in two Xenopus systems.
(A) MT severing by p60 Katanin regulates spindle length and architecture differently in
two Xenopus species. Depletion of p60 Katanin leads to larger spindles in Xenopus laevis.
In Xenopus tropicalis, p60 has an important role in establishing proper spindle length
and coordinating k-fiber and spindle MT populations such that k-fibers terminate at
the pole. (B) In early embryonic development, spindle size decreases by 30-40 mm
and is associated with changes in MT density, indicating differences in MT architecture.
Spindle size is controlled in part by regulation of the MT-depolymerizing kinesin-13
Kif2a by Importin a. Importin a can be membrane-bound, releasing Kif2a to act on
the spindle, or in the cytoplasmwhere it inhibits Kif2a. Therefore, the regulation of Kif2a,
and ultimately spindle size, is dependent on the membrane-to-cytoplasm or surface
area-to-volume ratio of the cell.