All through mouse embryonic advancement, neural progenitors lengthen the Smoothened G1 phase of your cell cycle and this continues to be recommended to get a cause, instead of a consequence, of neurogenesis. To investigate irrespective of whether G1 lengthening p38 MAPK alone might bring about the switch of cortical progenitors from proliferation to neurogenesis, we manipulated the expression of cdk/cyclin complexes and discovered that cdk4/cyclinD1 overexpression prevents G1 lengthening with no affecting cell growth, cleavage plane, or cell cycle synchrony with interkinetic nuclearmigration. Especially, overexpression of cdk4/cyclinD1 inhibited neurogenesis though raising the generation and expansion of basal ( intermediate) progenitors, leading to a thicker subventricular zone and larger surface place of the postnatal cortex originating from cdk4/cyclinD1-transfected progenitors. Conversely, lengthening of G1 by cdk4/cyclinD1-RNAi displayed the opposite effects. Thus, G1 lengthening is critical and enough to switch neural progenitors to neurogenesis, and overexpression of cdk4/cyclinD1 is usually used to increase progenitor expansion and, probably, cortical surface spot.