Figure 10

Pax6 expression during cell cycle progression and a model of cell cycle-dependent Pax6 regulation. A model of dynamic Pax6 expression during retinogenesis is depicted. Pax6 protein levels decrease in progenitor cells during the transition from the preneurogenic (indicated with an asterisk) to the neurogenic stage. Neurogenic progenitors express low levels of Pax6 protein, which is essential for maintaining the proliferative state, especially the reentry of S phase. The cohort of S phase cells contains a relatively uniform level of low Pax6. Upon entering into the G2/M phase, the neurogenic progenitor population displays more divergent Pax6 levels, with a subset of progenitor cells showing increased or decreased Pax6 protein expression depending on the developmental stage. Because postmitotic neurons contain distinct levels of Pax6 protein, the divergence of Pax6 expression during the G2/M phase may forecast cell fate specification at or prior to the G2 phase of the cell cycle. Postmitotic neurons achieve and maintain specific and distinct levels of Pax6 during differentiation. RGC, retinal ganglion cell.