Chronic wounds are a common and debilitating complication for the diabetic population. It is challenging to study the development of chronic wounds in human patients; by the time it is clear that a wound is chronic, the early phases of wound healing have passed and can no longer be studied. Because of this limitation, mouse models have been employed to better understand the early phases of chronic wound formation. In the past few years, a series of reports have highlighted the importance of reactive oxygen species and bacterial biofilms in the development of chronic wounds in diabetics. We review these recent findings and discuss mouse models that are being utilized to enhance our understanding of these potentially important contributors to chronic wound formation in diabetic patients.
In Drosophila melanogaster, the loss of activator de2f1 leads to a severe reduction in cell proliferation and repression of E2F targets. To date, the only known way to rescue the proliferation block in de2f1 mutants was through the inactivation of dE2F2. This suggests that dE2F2 provides a major contribution to the de2f1 mutant phenotype. Here, we report that in mosaic animals, in addition to de2f2, the loss of a DEAD box protein Belle (Bel) also rescues proliferation of de2f1 mutant cells. Surprisingly, the rescue occurs in a dE2F2-independent manner since the loss of Bel does not relieve dE2F2-mediated repression. In the eye disc, bel mutant cells fail to undergo a G 1 arrest in the morphogenetic furrow, delay photoreceptor recruitment and differentiation, and show a reduction of the transcription factor Ci155. The down-regulation of Ci155 is important since it is sufficient to partially rescue proliferation of de2f1 mutant cells. Thus, mutation of bel relieves the dE2F2-mediated cell cycle arrest in de2f1 mutant cells through a novel Ci155-dependent mechanism without functional inactivation of the dE2F2 repressor.Cell proliferation and differentiation are precisely coordinated during the development of a multicellular organism. The loss of such control may ultimately lead to defects in development and cancer. E2F transcription factors are important regulators of the cell cycle and critical downstream targets of the retinoblastoma (pRB) tumor suppressor protein (12). In spite of remarkable progress, dissecting the pRB pathway in mammalian cells remains a challenging task. One issue arises from functional redundancy and compensation among E2F and pRB family members. In the past years, Drosophila melanogaster has been recognized as a valuable tool for understanding various aspects of E2F biology. This is mainly due to the high conservation in cell cycle regulation between flies and mammals and the relative simplicity of the E2F/pRB module in Drosophila. In Drosophila, there are two E2F genes. As mammalian counterparts, their products can be classified as repressors (dE2F2) and activators (dE2F1).Analysis of dE2F single-and double-mutant animals has provided insights into the normal function of dE2Fs during development. de2f1 mutant larva are severely retarded in larval growth and show a strong reduction in S phases and the expression of E2F targets. Unexpectedly, these defects are largely suppressed in de2f1 de2f2 double mutants. This suggests that the de2f1 mutant phenotype is not entirely due to the absence of activator dE2F1 but rather, to some extent, is due to the presence of the "unchecked" repressor dE2F2 (18). This result is particularly striking since de2f2 mutants are viable and develop normally (5, 18). Why "unchecked" dE2F2 has such a strong effect on cell proliferation in the absence of dE2F1 is not clear. A possible explanation, supported by gene expression profiling (11), is that, in de2f1 mutant cells, dE2F2 inappropriately represses dE2F1-specific genes that are critical for cell proliferation. ...
SUMMARY E2F/DP transcription factors regulate cell proliferation and apoptosis. Here, we investigated the mechanism of the resistance of Drosophilad DP mutants to irradiation-induced apoptosis. Contrary to the prevailing view, this is not due to an inability to induce the apoptotic transcriptional program, since we show that this program is induced, but rather due to a mitochondrial dysfunction of dDP mutants. We attribute this defect to E2F/DP-dependent control of expression of mitochondria associated genes. Genetic attenuation of several of these E2F/DP targets mimics the dDP mutant mitochondrial phenotype and protects from irradiation-induced apoptosis. Significantly, the role of E2F/DP in the regulation of mitochondrial function is conserved between flies and humans. Thus, our results uncovered a role of E2F/DP in the regulation of mitochondrial function and demonstrate that this aspect of E2F regulation is critical for the normal induction of apoptosis in response to irradiation.
BackgroundIn response to a wound, fibroblasts are activated to migrate toward the wound, to proliferate and to contribute to the wound healing process. We hypothesize that changes in pre-mRNA processing occurring as fibroblasts enter the proliferative cell cycle are also important for promoting their migration.ResultsRNA sequencing of fibroblasts induced into quiescence by contact inhibition reveals downregulation of genes involved in mRNA processing, including splicing and cleavage and polyadenylation factors. These genes also show differential exon use, especially increased intron retention in quiescent fibroblasts compared to proliferating fibroblasts. Mapping the 3′ ends of transcripts reveals that longer transcripts from distal polyadenylation sites are more prevalent in quiescent fibroblasts and are associated with increased expression and transcript stabilization based on genome-wide transcript decay analysis. Analysis of dermal excisional wounds in mice reveals that proliferating cells adjacent to wounds express higher levels of cleavage and polyadenylation factors than quiescent fibroblasts in unwounded skin. Quiescent fibroblasts contain reduced levels of the cleavage and polyadenylation factor CstF-64. CstF-64 knockdown recapitulates changes in isoform selection and gene expression associated with quiescence, and results in slower migration.ConclusionsOur findings support cleavage and polyadenylation factors as a link between cellular proliferation state and migration.Electronic supplementary materialThe online version of this article (10.1186/s13059-018-1551-9) contains supplementary material, which is available to authorized users.
The growth suppressive function of the retinoblastoma (pRB) tumor suppressor family is largely attributed to its ability to negatively regulate the family of E2F transcriptional factors and, as a result, to repress E2F-dependent transcription. Deregulation of the pRB pathway is thought to be an obligatory event in most types of cancers. The large number of mammalian E2F proteins is one of the major obstacles that complicate their genetic analysis. In Drosophila, the E2F family consists of only two members. They are classified as an activator (dE2F1) and a repressor (dE2F2). It has been previously shown that proliferation of de2f1 mutant cells is severely reduced due to unchecked activity of the repressor dE2F2 in these cells. We report here a mosaic screen utilizing the de2f1 mutant phenotype to identify suppressors that overcome the dE2F2/RBF-dependent proliferation block. We have isolated l(3)mbt and B52, which are known to be required for dE2F2 function, as well as genes that were not previously linked to the E2F/pRB pathway such as Doa, gfzf, and CG31133. Inactivation of gfzf, Doa, or CG31133 does not relieve repression by dE2F2. We have shown that gfzf and CG31133 potentiate E2F-dependent activation and synergize with inactivation of RBF, suggesting that they may act in parallel to dE2F. Thus, our results demonstrate the efficacy of the described screening strategy for studying regulation of the dE2F/RBF pathway in vivo.T HE family of E2F transcription factors and retinoblastoma (pRB) family tumor suppressor proteins play a pivotal role in control of cell proliferation(reviewed in Trimarchi and Lees 2002;Blais and Dynlacht 2004;Dimova and Dyson 2005;Degregori and Johnson 2006). Although E2F is involved in a variety of cellular activities, the best understood function of E2F is to regulate transcription of genes at the G 1 /S transition. Among E2F targets are genes that encode regulators of S-phase entry and components of the DNA replication machinery. In mammals, there are eight E2F genes. E2F-1 through E2F-6 function as heterodimers with a DP subunit, while E2F-7 and E2F-8 do not require DP to bind to DNA. In spite of structural similarities among E2F proteins, E2F-1, E2F-2, and E2F-3a are predominately involved in activation of gene expression while the group E2F-3b, E2F-4, E2F-5, E2F-6, E2F-7, and E2F-8 behave as repressors. In quiescent cells, when activity of cyclindependent kinases (cdks) is low, repressor E2Fs are complexed with the pRB family members (also called pocket proteins) and repress expression of E2F regulated genes. The prevailing mechanism of the repression is thought to be through the direct recruitment of histone deacetylases, histone methylases, and other corepressor complexes by pocket proteins to E2F regulated promoters. Upon entry into the cell cycle, mitogenic stimulation leads to an increase in the activity of G 1 cdks, which phosphorylate pRB family members and disrupt their interaction with E2Fs. This coincides with displacement of the repressor E2Fs, appearance of free ...
The retinoblastoma protein (pRB) negatively regulates cell proliferation by limiting the activity of the family of E2F transcription factors. In Drosophila, mutation of the DEAD-box helicase belle (bel) relieves an E2F/pRB induced G1 cell cycle arrest; however, the mechanism of this rescue is unknown. Here, we show that the level of the cyclin-dependent kinase inhibitor Dacapo (Dap), homolog of mammalian p21/p27, is strongly reduced both in bel mutant cells in vivo and in tissue culture cells depleted of Bel by RNA interference. Interestingly, the loss of bel also partially alleviates an ectopically induced G1 cell cycle arrest. Additionally, we show that Bel undergoes nucleocytoplasmic shuttling. Thus, inactivation of bel renders cells less sensitive to several anti-proliferative signals inducing G1 arrest.
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