Project description:E2F transcription factors control the expression of a large network of cell cycle genes and are essential for S-phase entry. Cancers often demonstrate upregulation of E2F target gene expression, which can be partially explained by loss of the G1/S checkpoint and increased percentages of replicating cells. However, we now demonstrate that cycling individual neoplastic cells can display abnormally high levels of E2F-dependent transcription using single cell RNA sequencing. To test how this affects their DNA damage response, we deleted the atypical E2F transcriptional repressors (E2F7/8) in untransformed cells. This intervention specifically increased the expression of E2F target genes during S and G2-phase without overriding the G1/S-checkpoint. Live cell imaging revealed that cells in S-G2 with deregulated E2F activity failed to arrest and underwent unscheduled mitosis after neocarzinostatin-induced DNA damage. In contrast, cells with physiological E2F-activity completed S-phase and then activated the APC/C-Cdh1 via repression of the E2F-target Emi1, leading to a G1-like arrest. Interestingly, ~30% of these 4N-G1 cells could eventually inactivate APC/CCdh1 to execute a second round of DNA replication and mitosis, resulting in the formation of tetraploid cells. Cells with deregulated E2F activity fail to exit the cell cycle after DNA damage and likely acquire more genetic changes. The observed elevated E2F-dependent transcription in cancer cells could therefore potentially promote malignant progression and reduce sensitivity to anti-cancer drugs.
Project description:Loss of the retinal pigment epithelium (RPE) due to dysfunction or disease can lead to blindness in humans. Harnessing the intrinsic ability of the RPE to self-repair is an attractive therapeutic strategy; however, mammalian RPE is limited in its regenerative capacity. Zebrafish possess tremendous intrinsic regenerative potential in ocular tissues, including the RPE, but little is known about the mechanisms that drive RPE regeneration. Here, utilizing zebrafish, we identified elements of the immune response as critical mediators of intrinsic RPE regeneration. Macrophages/microglia are responsive to RPE damage and are required for the timely progression of the regenerative response and our data highlight that inflammation post-RPE injury is also critical for normal RPE regeneration. These data are the first to identify the molecular and cellular underpinnings of RPE regeneration in any system and hold significant potential for translational approaches aimed towards promoting a pro-regenerative environment in mammals.
Project description:Microarray analysis of murine retinal light damage reveals changes in iron regulatory, complement, and antioxidant genes in the neurosensory retina and isolated retinal pigment epithelium (RPE). With the advent of microarrays representing most of the transcriptome and techniques to obtain RNA from the isolated RPE monolayer, we have probed the response of the RPE and neurosensory retina (NSR) to light damage.
Project description:The DNA damage checkpoint senses the presence of DNA lesions and controls the cellular response thereto. A crucial DNA damage signal is single-stranded DNA (ssDNA), which is frequently found at sites of DNA damage and recruits the sensor checkpoint kinase Mec1-Ddc2. However, how this signal – and therefore the cells’ DNA damage load – is quantified, is poorly understood. Here, we use genetic manipulation of DNA end resection at a site-specific DNA double-strand break (DSB) in budding yeast to generate quantitatively different DNA damage (ssDNA) signals. Interestingly, two major targets of the Mec1-Ddc2 kinase – Rad53 and γH2A – differ in their response to the ssDNA signal, indicating distinct signalling circuits within the checkpoint. The local checkpoint signalling circuit leading to γH2A phosphorylation is non-quantitative and unresponsive to increased amounts of damage-associated Mec1-Ddc2 kinase. In contrast, the global checkpoint signalling circuit, which triggers Rad53 activation, integrates the ssDNA signal quantitatively. We find that not only Mec1-Ddc2 association, but also loading of the 9-1-1 co-sensor complex is enhanced during ongoing resection. Moreover, we can uncouple global checkpoint activation from the amount of Mec1-Ddc2 kinase at the lesion by using mutant conditions that hyper-activate the 9-1-1 signalling axis and at the same time show reduced amounts of damage-associated Mec1-Ddc2 kinase. We therefore propose that a key function of the 9-1-1 complex and the downstream checkpoint mediators is to generate a checkpoint response, which is quantitative and proportional to the cellular DNA damage load. The DNA damage checkpoint senses the presence of DNA lesions and controls the cellular response thereto. A crucial DNA damage signal is single-stranded DNA (ssDNA), which is frequently found at sites of DNA damage and recruits the sensor checkpoint kinase Mec1-Ddc2. However, how this signal – and therefore the cells’ DNA damage load – is quantified, is poorly understood. Here, we use genetic manipulation of DNA end resection at a site-specific DNA double-strand break (DSB) in budding yeast to generate quantitatively different DNA damage (ssDNA) signals. Interestingly, two major targets of the Mec1-Ddc2 kinase – Rad53 and γH2A – differ in their response to the ssDNA signal, indicating distinct signalling circuits within the checkpoint. The local checkpoint signalling circuit leading to γH2A phosphorylation is non-quantitative and unresponsive to increased amounts of damage-associated Mec1-Ddc2 kinase. In contrast, the global checkpoint signalling circuit, which triggers Rad53 activation, integrates the ssDNA signal quantitatively. We find that not only Mec1-Ddc2 association, but also loading of the 9-1-1 co-sensor complex is enhanced during ongoing resection. Moreover, we can uncouple global checkpoint activation from the amount of Mec1-Ddc2 kinase at the lesion by using mutant conditions that hyper-activate the 9-1-1 signalling axis and at the same time show reduced amounts of damage-associated Mec1-Ddc2 kinase. We therefore propose that a key function of the 9-1-1 complex and the downstream checkpoint mediators is to generate a checkpoint response, which is quantitative and proportional to the cellular DNA damage load.
Project description:Microarray analysis of murine retinal light damage reveals changes in iron regulatory, complement, and antioxidant genes in the neurosensory retina and isolated retinal pigment epithelium (RPE). With the advent of microarrays representing most of the transcriptome and techniques to obtain RNA from the isolated RPE monolayer, we have probed the response of the RPE and neurosensory retina (NSR) to light damage. Mice were exposed to 10,000 lux cool white fluorescent light for 18 hours and sacrificed 4 hours after photic injury. NSR and isolated RPE were collected, and RNA was isolated. DNA microarray hybridization was conducted as described in the Affymetrix GeneChip Expression Analysis Technical Manual. Microarray analysis was performed using probe intensity data derived from the Mouse Gene 1.0 ST Array. For the genes of interest, confirmation of gene expression was done using quantitative real-time PCR. Immunofluorescence assessed protein levels and localization.