Cell fate decisions and patterning in the vertebrate retina: the importance of timing, asymmetry, polarity and waves.

The differentiation of distinct cell populations in the retina is a multi-step process that involves cell cycle exit, migration, and dramatic changes of cell morphology. All these steps are tightly controlled by multiple regulatory pathways, which involve both cell-autonomous networks of transcription factors and cell-cell signaling events. Additional regulatory inputs into cell fate decisions have been recently suggested: accumulating evidence shows that the timing of cell cycle exit, the orientation of the mitotic spindle during the last cell division, and the polarity of neuronal progenitor cells could play important roles in cell fate determination.