Kinetochore fibers are not involved in the formation of the first meiotic spindle in mouse oocytes, but control the exit from the first meiotic M phase
S. Brunet et al., Kinetochore fibers are not involved in the formation of the first meiotic spindle in mouse oocytes, but control the exit from the first meiotic M phase, J CELL BIOL, 146(1), 1999, pp. 1-11
During meiosis, two successive divisions occur without any intermediate S p
hase to produce haploid gametes. The first meiotic division is unique in th
at homologous chromosomes are segregated while the cohesion between sister
chromatids is maintained, resulting in a reductional division. Moreover, th
e duration of the first meiotic M phase is usually prolonged when compared
with mitotic M phases lasting 8 h in mouse oocytes.
We investigated the spindle assembly pathway and its role in the progressio
n of the first meiotic M phase In mouse oocytes. During the first 4 h, a bi
polar spindle forms and the chromosomes congress near the equatorial plane
of the spindle without stable kinetochore-microtubule end interactions. Thi
s late prometaphase spindle is then maintained for 4 h with chromosomes osc
illating in the central region of the spindle. The kinetochore-microtubule
end interactions are set up at the end of the first meiotic M phase (8 h af
ter entry into M phase). This event allows the final alignment of the chrom
osomes and exit from metaphase. The continuous presence of the prometaphase
spindle is not required for progression of the first meiotic M phase. Fina
lly, the ability of kinetochores to interact with microtubules is acquired
at the end of the first meiotic M phase and determines the timing of polar
body extrusion.