Requirement for E2F4 in development of ventral telencephalon and visual system

Abstract

New functions of the Rb/E2F pathway in developmental processes are emerging. The goal of this research was to identify the role of the E2F4 transcription factor during early nervous system development. First, I addressed whether E2F4 was required for the development of the telencephalon. Analysis of E2F4 deficient mouse embryos revealed that loss of E2F4 led to severe morphological defects in early ventral telencephalic development. Specifically, ganglionic eminences were absent and expression of the regional homeobox transcription factors was significantly reduced, suggesting that E2F4 is involved in the regulation of genes important for brain patterning. E2F4 deficiency also caused a reduction in neural stem cell number, indicating the requirement for E2F4 in regulation of neural stem cell self-renewal. To account for the aberrant telencephalic development, we showed that E2F4 deficiency lead to aberrant Shh signaling and impaired activity of forebrain-specific Shh enhancers. Activation of the Shh pathway with a Hh agonist restored cells expressing Nkx2.1 in explant cultures, as well as neural stem cell self-renewal. Finally, I identified a novel genetic interaction between E2F4 and Shh pathway in early telencephalic development. These studies demonstrated that E2F4 was required for ventral telencephalic development. Next, I determined whether E2F4 was required for eye patterning, which is closely linked to ventral telencephalic development and is regulated by Shh. I found that early eye morphogenesis and patterning was perturbed, such that optic stalk specific genes extended into the ventral optic cup with simultaneous reduction of the neural retinal markers. Also, Shh signaling was disrupted in the absence of E2F4. The Shh expression domain in the ventral hypothalamus was split and Shh activity was expanded into the ventral optic cup. These studies revealed a key role for E2F4 in early eye patterning. Overall, my findings reveal a novel requirement for E2F4 during early telencephalic and eye development, as well as in neural stem cells regulation.