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author:("pacap, Marek")
1.  Division and apoptosis in the E2f-deficient retina 
Nature  2009;462(7275):925.
E2fs 1-3, also known as activating E2fs, are viewed broadly as critical positive cell cycle regulators. They induce transcription and can drive cells out of quiescence. In flies and mammalian fibroblasts removing activating E2fs causes cell cycle arrest, suggesting an obligate proliferative role 1, 2. However, arrest is indirect as it is alleviated by removing the repressive E2f, dE2f2, in flies, or the tumor suppressor p53 in fibroblasts 3–5. Whether activating E2fs are required for division in vivo is thus an area of lively debate 6. Activating E2fs are also well known pro-apoptotic factors, a defense against oncogenesis 7. In some contexts E2f1 limits irradiation-induced apoptosis 8, 9, but in flies this occurs through repression of hid and the mammalian equivalent, Smac/Diablo is induced not repressed by E2f1 10, and in keratinoctyes it occurs indirectly through induction of DNA repair targets 11. Thus, a direct pro-survival function for activating E2fs in mammals has not been established. To address E2f1-3 function in vivo we focused on the mouse retina, a relatively simple CNS component that can be manipulated without compromising viability and has provided considerable insight into development and cancer 12–14. Here, we show that E2f1-3-deficient retinal progenitor cells or activated Muller glia divide. In the absence of activating E2fs, the Myc family drives proliferation. However, down-regulation of Sirt1, a p53 deacetylase, leads to hyperacetylation of p53 and cell death. Thus, activating E2fs are not universally required for mammalian cell division, but have an unexpected prosurvival role in development.
doi:10.1038/nature08544
PMCID: PMC2813224  PMID: 20016601
E2f; Neurogenesis; p21Cip1; p57Kip2; Histone deacetylase; Sirtuin; p53; Resveratrol
2.  Noninvasive, In Vivo Assessment of Mouse Retinal Structure Using Optical Coherence Tomography 
PLoS ONE  2009;4(10):e7507.
Background
Optical coherence tomography (OCT) is a novel method of retinal in vivo imaging. In this study, we assessed the potential of OCT to yield histology-analogue sections in mouse models of retinal degeneration.
Methodology/Principal Findings
We achieved to adapt a commercial 3rd generation OCT system to obtain and quantify high-resolution morphological sections of the mouse retina which so far required in vitro histology. OCT and histology were compared in models with developmental defects, light damage, and inherited retinal degenerations. In conditional knockout mice deficient in retinal retinoblastoma protein Rb, the gradient of Cre expression from center to periphery, leading to a gradual reduction of retinal thickness, was clearly visible and well topographically quantifiable. In Nrl knockout mice, the layer involvement in the formation of rosette-like structures was similarly clear as in histology. OCT examination of focal light damage, well demarcated by the autofluorescence pattern, revealed a practically complete loss of photoreceptors with preservation of inner retinal layers, but also more subtle changes like edema formation. In Crb1 knockout mice (a model for Leber's congenital amaurosis), retinal vessels slipping through the outer nuclear layer towards the retinal pigment epithelium (RPE) due to the lack of adhesion in the subapical region of the photoreceptor inner segments could be well identified.
Conclusions/Significance
We found that with the OCT we were able to detect and analyze a wide range of mouse retinal pathology, and the results compared well to histological sections. In addition, the technique allows to follow individual animals over time, thereby reducing the numbers of study animals needed, and to assess dynamic processes like edema formation. The results clearly indicate that OCT has the potential to revolutionize the future design of respective short- and long-term studies, as well as the preclinical assessment of therapeutic strategies.
doi:10.1371/journal.pone.0007507
PMCID: PMC2759518  PMID: 19838301
3.  Rb-Mediated Neuronal Differentiation through Cell-Cycle–Independent Regulation of E2f3a 
PLoS Biology  2007;5(7):e179.
It has long been known that loss of the retinoblastoma protein (Rb) perturbs neural differentiation, but the underlying mechanism has never been solved. Rb absence impairs cell cycle exit and triggers death of some neurons, so differentiation defects may well be indirect. Indeed, we show that abnormalities in both differentiation and light-evoked electrophysiological responses in Rb-deficient retinal cells are rescued when ectopic division and apoptosis are blocked specifically by deleting E2f transcription factor (E2f) 1. However, comprehensive cell-type analysis of the rescued double-null retina exposed cell-cycle–independent differentiation defects specifically in starburst amacrine cells (SACs), cholinergic interneurons critical in direction selectivity and developmentally important rhythmic bursts. Typically, Rb is thought to block division by repressing E2fs, but to promote differentiation by potentiating tissue-specific factors. Remarkably, however, Rb promotes SAC differentiation by inhibiting E2f3 activity. Two E2f3 isoforms exist, and we find both in the developing retina, although intriguingly they show distinct subcellular distribution. E2f3b is thought to mediate Rb function in quiescent cells. However, in what is to our knowledge the first work to dissect E2f isoform function in vivo we show that Rb promotes SAC differentiation through E2f3a. These data reveal a mechanism through which Rb regulates neural differentiation directly, and, unexpectedly, it involves inhibition of E2f3a, not potentiation of tissue-specific factors.
Author Summary
The retinoblastoma protein (Rb), an important tumor suppressor, blocks division and death by inhibiting the E2f transcription factor family. In contrast, Rb is thought to promote differentiation by potentiating tissue-specific transcription factors, although differentiation defects in Rb null cells could be an indirect consequence of E2f-driven division and death. Here, we resolve different mechanisms by which Rb controls division, death, and differentiation in the retina. Removing E2f1 rescues aberrant division of differentiating Rb-deficient retinal neurons, as well as death in cells prone to apoptosis, and restores both normal differentiation and function of major cell types, such as photoreceptors. However, Rb-deficient starburst amacrine neurons differentiate abnormally even when E2f1 is removed, providing an unequivocal example of a direct role for Rb in neuronal differentiation. Rather than potentiating a cell-specific factor, Rb promotes starburst cell differentiation by inhibiting another E2f, E2f3a. This cell-cycle–independent activity broadens the importance of the Rb–E2f pathway, and suggests we should reassess its role in the differentiation of other cell types.
The retinoblastoma protein (Rb), a tumor suppressor, promotes the differentiation of starburst amacrine cells in the retina by inhibiting the transcription factor E2f3a, whereas it suppresses retinal cell division and death by inhibiting E2f1.
doi:10.1371/journal.pbio.0050179
PMCID: PMC1914394  PMID: 17608565

Results 1-3 (3)