Cyclin E-p27 opposition and regulation of the G1 phase of the cell cycle in the murine neocortical PVE: A quantitative analysis of mRNA in situ hybridization
I. Delalle et al., Cyclin E-p27 opposition and regulation of the G1 phase of the cell cycle in the murine neocortical PVE: A quantitative analysis of mRNA in situ hybridization, CEREB CORT, 9(8), 1999, pp. 824-832
We have analyzed the expression patterns of mRNAs of five cell cycle relate
d proteins in the ventricular zone of the neocortical cerebral wall over th
e course of the neuronogenetic interval in the mouse. One set of mRNAs (cyc
lin E and p21) are initially expressed at high levels but expression then f
alls to a low asymptote. A second set (p27, cyclin B and cdk2) are initiall
y expressed at low levels but ascend to peak levels only to decline again.
These patterns divide the overall neuronogenetic interval into three phases
. In phase 1 cyclin E and p21 levels of mRNA expression are high, while tho
se of mRNAs of p27, cdk2 and cyclin B are low. In this phase the fraction o
f cells leaving the cycle after each mitosis, Q, is low and the duration of
the G1 phase, T-G1, is short. In phase 2 levels of expression of cyclin E
and p21 fall to asymptote while levels of expression of mRNA of the other t
hree proteins reach their peaks. Q increases to approach 0.5 and T-G1 incre
ases even more rapidly to approach its maximum length. In phase 3 levels of
expression of cyclin E and p21 mRNAs remain low and those of the mRNAs of
the other three proteins fall. T-G1 becomes maximum and a rapidly increases
to 1.0. The character of these phases can be understood in part as consequ
ences of the reciprocal regulatory influence of p27 and cyclin E and of the
rate limiting functions of p27 at the restriction point and of cyclin E at
the G1 to S transition.