The mechanisms through which cell-cycle control and cell-fate decisions are coordinated in proliferating stem cell populations are largely unknown. Here, we show that E2f3 isoforms, which control cell-cycle progression in cooperation with the retinoblastoma protein (pRb), have critical effects during developmental and adult neurogenesis. Loss of either E2f3 isoform disrupts Sox2 gene regulation and the balance between precursor maintenance and differentiation in the developing cortex. Both isoforms target the Sox2 locus to maintain baseline levels of Sox2 expression but antagonistically regulate Sox2 levels to instruct fate choices. E2f3-mediated regulation of Sox2 and precursor cell fate extends to the adult brain, where E2f3a loss results in defects in hippocampal neurogenesis and memory formation. Our results demonstrate a mechanism by which E2f3a and E2f3b differentially regulate Sox2 dosage in neural precursors, a finding that may have broad implications for the regulation of diverse stem cell populations.

Cell cycle proteins are important regulators of diverse cell fate decisions, and in this capacity have pivotal roles in neurogenesis and brain development. The mechanisms by which cell cycle regulation is integrated with cell fate control in the brain and other tissues are poorly understood, and an outstanding question is whether the cell cycle machinery regulates fate decisions directly or instead as a secondary consequence of proliferative control. Identification of the genes targeted by E2 promoter binding factor (E2f) transcription factors, effectors of the pRb/E2f cell cycle pathway, will provide essential insights into these mechanisms. We identified the promoter regions bound by three neurogenic E2f factors in neural precursor cells in a genome-wide manner. Through bioinformatic analyses and integration of published genomic data sets we uncovered hundreds of transcriptionally active E2f-bound promoters corresponding to genes that control cell fate processes, including key transcriptional regulators and members of the Notch, fibroblast growth factor, Wnt and Tgf-β signaling pathways. We also demonstrate a striking enrichment of the CCCTC binding factor transcription factor (Ctcf) at E2f3-bound nervous system-related genes, suggesting a potential regulatory co-factor for E2f3 in controlling differentiation. Finally, we provide the first demonstration of extensive tissue specificity among E2f target genes in mammalian cells, whereby E2f3 promoter binding is well conserved between neural and muscle precursors at genes associated with cell cycle processes, but is tissue-specific at differentiation-associated genes. Our findings implicate the cell cycle pathway as a widespread regulator of cell fate genes, and suggest that E2f3 proteins control cell typespecific differentiation programs by regulating unique sets of target genes. This work significantly enhances our understanding of how the cell cycle machinery impacts cell fate and differentiation, and will importantly drive further discovery regarding the mechanisms of cell fate control and transcriptional regulation in the brain, as well as in other tissues.

factor 8 (Fgf8), Sonic hedgehog (Shh), bone morphogenetic proteins (BMPs)2,4,6 and 7, and Wnts 2b,3a,5a and 7a control the regional expression of specific transcription factors. Some of these secreted factors are expressed at the region of the ZLI, being Shh the main factor studied controlling proliferation, regionalization and polarity in the diencephalic segments. Nevertheless, despite the importance of the ZLI, the mechanism of its formation remains poorly understood.In this work, we have studied the molecular mechanisms for generating a permissive territory for Shh expression in the ZLI, by using experimental embryology techniques: insertion of microbarriers and protein soaked beads in the diencephalic neuroepithelium. We have analyzed the molecular interactions between genes expressed in the diencephalon such as Shh, Glis, Wnts, Fgf and L-fng, among others, by in situ hybridization. Our results let us to describe new molecular processes regulating the establishment of the ZLI compartment.

factor 8 (Fgf8), Sonic hedgehog (Shh), bone morphogenetic proteins (BMPs)2,4,6 and 7, and Wnts 2b,3a,5a and 7a control the regional expression of specific transcription factors. Some of these secreted factors are expressed at the region of the ZLI, being Shh the main factor studied controlling proliferation, regionalization and polarity in the diencephalic segments. Nevertheless, despite the importance of the ZLI, the mechanism of its formation remains poorly understood.In this work, we have studied the molecular mechanisms for generating a permissive territory for Shh expression in the ZLI, by using experimental embryology techniques: insertion of microbarriers and protein soaked beads in the diencephalic neuroepithelium. We have analyzed the molecular interactions between genes expressed in the diencephalon such as Shh, Glis, Wnts, Fgf and L-fng, among others, by in situ hybridization. Our results let us to describe new molecular processes regulating the establishment of the ZLI compartment.

No abstract