Local phosphatase regulation is needed at kinetochores to silence the mitotic checkpoint (a.k.a. spindle assembly checkpoint SAC). A key event in this regard is the dephosphorylation of MELT repeats ...on KNL1, which removes SAC proteins from the kinetochore, including the BUB complex. We show here that PP1 and PP2A-B56 phosphatases are primarily required to remove Polo-like kinase 1 (PLK1) from the BUB complex, which can otherwise maintain MELT phosphorylation in an autocatalytic manner. This appears to be their principal role in the SAC because both phosphatases become redundant if PLK1 is inhibited or BUB-PLK1 interaction is prevented. Surprisingly, MELT dephosphorylation can occur normally under these conditions even when the levels or activities of PP1 and PP2A are strongly inhibited at kinetochores. Therefore, these data imply that kinetochore phosphatase regulation is critical for the SAC, but primarily to restrain and extinguish autonomous PLK1 activity. This is likely a conserved feature of the metazoan SAC, since the relevant PLK1 and PP2A-B56 binding motifs have coevolved in the same region on MADBUB homologues.
PP1 and PP2A-B56 are major serine/threonine phosphatase families that achieve specificity by colocalizing with substrates. At the kinetochore, however, both phosphatases localize to an almost ...identical molecular space and yet they still manage to regulate unique pathways and processes. By switching or modulating the positions of PP1/PP2A-B56 at kinetochores, we show that their unique downstream effects are not due to either the identity of the phosphatase or its precise location. Instead, these phosphatases signal differently because their kinetochore recruitment can be either inhibited (PP1) or enhanced (PP2A) by phosphorylation inputs. Mathematical modeling explains how these inverse phospho-dependencies elicit unique forms of cross-regulation and feedback, which allows otherwise indistinguishable phosphatases to produce distinct network behaviors and control different mitotic processes. Furthermore, our genome-wide analysis suggests that these major phosphatase families may have evolved to respond to phosphorylation inputs in opposite ways because many other PP1 and PP2A-B56-binding motifs are also phospho-regulated.
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•PP1 and PP2A-B56 can functionally substitute for each other at the kinetochore•The major difference is their ability to respond to phospho-inputs in opposite ways•This underlies their distinct phenotypic behaviors•Many other signaling pathways also select for these same key features
Smith et al. investigate PP1 and PP2A-B56 specificity at kinetochores and conclude that the main difference between these phosphatases is their ability to respond in opposite ways to phosphorylation inputs. This allows them to produce distinct network behaviors and control different mitotic processes. These unique features have likely been exploited by many other signaling pathways throughout evolution.
Non-proliferating oocytes within avascular regions of the ovary are exquisitely susceptible to chemotherapy. Early menopause and sterility are unintended consequences of chemotherapy, and efforts to ...understand the oocyte apoptotic pathway may provide new targets for mitigating this outcome. Recently, the c-Abl kinase inhibitor imatinib mesylate (imatinib) has become the focus of research as a fertoprotective drug against cisplatin. However, the mechanism by which imatinib protects oocytes is not fully understood, and reports of the drug's efficacy have been contradictory. Using in vitro culture and subrenal grafting of mouse ovaries, we demonstrated that imatinib inhibits the cisplatin-induced apoptosis of oocytes within primordial follicles. We found that, before apoptosis, cisplatin induces c-Abl and TAp73 expression in the oocyte. Oocytes undergoing apoptosis showed downregulation of TAp63 and upregulation of Bax. While imatinib was unable to block cisplatin-induced DNA damage and damage response, such as the upregulation of p53, imatinib inhibited the cisplatin-induced nuclear accumulation of c-Abl/TAp73 and the subsequent downregulation of TAp63 and upregulation of Bax, thereby abrogating oocyte cell death. Surprisingly, the conditional deletion of Trp63, but not ΔNp63, in oocytes inhibited apoptosis, as well as the accumulation of c-Abl and TAp73 caused by cisplatin. These data suggest that TAp63 is the master regulator of cisplatin-induced oocyte death. The expression kinetics of TAp63, c-Abl and TAp73 suggest that cisplatin activates TAp63-dependent expression of c-Abl and TAp73 and, in turn, the activation of TAp73 by c-Abl-induced BAX expression. Our findings indicate that imatinib protects oocytes from cisplatin-induced cell death by inhibiting c-Abl kinase, which would otherwise activate TAp73-BAX-mediated apoptosis. Thus, imatinib and other c-Abl kinase inhibitors provide an intriguing new way to halt cisplatin-induced oocyte death in early follicles and perhaps conserve the endocrine function of the ovary against chemotherapy.
In this study, we explored the effects of oocytic phosphoinositide 3-kinase (PI3K) activation on folliculogensis by generating transgenic mice, in which the oocyte-specific Cre-recombinase induces ...the expression of constitutively active mutant PI3K during the formation of primordial follicles. The ovaries of neonatal transgenic (Cre+) mice showed significantly reduced apoptosis in follicles, which resulted in an excess number of follicles per ovary. Thus, the elevation of phosphatidylinositol (3,4,5)-trisphosphate levels within oocytes promotes the survival of follicles during neonatal development. Despite the increase in AKT phosphorylation, primordial follicles in neonatal Cre+ mice remained dormant demonstrating a nuclear accumulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). These primordial follicles containing a high level of nuclear PTEN persisted in postpubertal females, suggesting that PTEN is the dominant factor in the maintenance of female reproductive lifespan through the regulation of primordial follicle recruitment. Although the oocytic PI3K activity and PTEN levels were elevated, the activation of primordial follicles and the subsequent accumulation of antral follicles with developmentally competent oocytes progressed normally in prepubertal Cre+ mice. However, mature Cre+ female mice were anovulatory. Because postnatal day 50 Cre+ mice released cumulus-oocyte complexes with developmentally competent oocytes in response to super-ovulation treatment, the anovulatory phenotype was not due to follicular defects but rather endocrine abnormalities, which were likely caused by the excess number of overgrown follicles. Our current study has elucidated the critical role of oocytic PI3K activity in follicular function, as well as the presence of a PTEN-mediated mechanism in the prevention of immature follicle activation.
During embryonic development, mouse female germ cells enter meiosis in an anterior-to-posterior wave believed to be driven by retinoic acid. It has been proposed that ovarian follicle formation and ...activation follow the same general wave of meiotic progression; however, the precise anatomic specification of these processes has not been delineated. Here, we created a mouse line using Mvh, Gdf9, and Zp3 promoters to drive distinct temporal expression of three fluorescent proteins in the oocytes and to identify where the first follicle cohort develops. The fluorescent profile revealed that the first growing follicles consistently appeared in a specific region of the ovary, the anterior-dorsal region, which led us to analyze if meiotic onset occurred earlier in the dorsal ovarian region. Surprisingly, in addition to the anterior-to-posterior wave, we observed an early meiotic entry in the ventral region of the ovary. This additional anatomic stratification of meiosis contrasts with the localization of the initial follicle formation and activation in the dorsal region of the ovary. Therefore, our study suggests that the specification of cortical and medullar areas in the ventral and dorsal regions on the ovary, rather than the onset of meiosis, impacts where the first follicle activation event occurs.
The Müller-Lyer Illusion (MLI) has been suggested as a potential marker for the perceptual impairments observed in schizophrenia patients. Along with some positive symptoms, these deficits are not ...easily modeled in rodent experiments, and novel animal models are warranted. Previously, MK-801 was shown to reduce susceptibility to MLI in monkeys, raising the prospects of an effective perception-based model. Here, we evaluate the translational feasibility of the MLI task under NMDA receptor blockage as a primate model for schizophrenia. In Experiment 1, eight capuchin monkeys (
Sapajus
spp.) were trained on a touchscreen MLI task. Upon reaching the learning criteria, the monkeys were given ketamine (0.3 mg/kg; i.m.) or saline on four consecutive days and then retested on the MLI task. In Experiment 2, eight chronic schizophrenia patients (and eight matching controls) were tested on the Brentano version of the MLI. Under saline treatment, monkeys were susceptible to MLI, similarly to healthy human participants. Repeated ketamine administrations, however, failed to improve their performance as previous results with MK-801 had shown. Schizophrenic patients, on the other hand, showed a higher susceptibility to MLI when compared to healthy controls. In light of the present and previous studies, the MLI task shows consistent results across monkeys and humans. In spite of potentially being an interesting translational model of schizophrenia, the MLI task warrants further refinement in non-human primates and a broader sample of schizophrenia subtypes.
Response of cells and tissues to shear stress Espina, Jaime A.; Cordeiro, Marilia H.; Milivojevic, Milan ...
Journal of cell science,
09/2023, Letnik:
136, Številka:
18
Journal Article
Recenzirano
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ABSTRACT
Shear stress is essential for normal physiology and malignancy. Common physiological processes – such as blood flow, particle flow in the gut, or contact between migratory cell clusters and ...their substrate – produce shear stress that can have an impact on the behavior of different tissues. In addition, shear stress has roles in processes of biomedical interest, such as wound healing, cancer and fibrosis induced by soft implants. Thus, understanding how cells react and adapt to shear stress is important. In this Review, we discuss in vivo and in vitro data obtained from vascular and epithelial models; highlight the insights these have afforded regarding the general mechanisms through which cells sense, transduce and respond to shear stress at the cellular levels; and outline how the changes cells experience in response to shear stress impact tissue organization. Finally, we discuss the role of shear stress in collective cell migration, which is only starting to be appreciated. We review our current understanding of the effects of shear stress in the context of embryo development, cancer and fibrosis, and invite the scientific community to further investigate the role of shear stress in these scenarios.
The environmental dioxin 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is classified as a Group 1 human carcinogen and teratogenic agent. We hypothesize that TCDD-induced oxidative stress may also ...interfere with mitochondrial ATP-sensitive potassium channels (mitoKATP), which are known to regulate and to be regulated by mitochondrial redox state. We investigated the effects of an acute treatment of male Wistar rats with TCDD (50 μg/kg i.p.) and measured the regulation of cardiac mitoKATP. While the function of cardiac mitochondria was slightly depressed, mitoKATP activity was 52% higher in animals treated with TCDD. The same effects were not observed in liver mitochondria isolated from the same animals. Our data also shows that regulation of mitochondrial ROS production by mitoKATP activity is different in both groups. To our knowledge, this is the first report to show that TCDD increases mitoKATP activity in the heart, which may counteract the increased oxidative stress caused by the dioxin during acute exposure.
•Acute TCDD treatment of Wistar rats causes cardiac oxidative stress.•Acute TCDD treatment causes cardiac mitochondrial alterations.•Mitochondrial liver vs. heart alterations are distinct.•TCDD treatment resulted in altered activity of cardiac mitochondrial K-ATP channels.
Dioxin alters the regulation of cardiac mitochondrial ATP-sensitive potassium channels and disturbs mitochondrial physiology.
Tissue interplay during morphogenesis Espina, Jaime A.; Cordeiro, Marilia H.; Barriga, Elias H.
Seminars in cell & developmental biology,
09/2023, Letnik:
147
Journal Article
Recenzirano
The process by which biological systems such as cells, tissues and organisms acquire shape has been named as morphogenesis and it is central to a plethora of biological contexts including embryo ...development, wound healing, or even cancer. Morphogenesis relies in both self-organising properties of the system and in environmental inputs (biochemical and biophysical). The classical view of morphogenesis is based on the study of external biochemical molecules, such as morphogens. However, recent studies are establishing that the mechanical environment is also used by cells to communicate within tissues, suggesting that this mechanical crosstalk is essential to synchronise morphogenetic transitions and self-organisation. In this article we discuss how tissue interaction drive robust morphogenesis, starting from a classical biochemical view, to finalise with more recent advances on how the biophysical properties of a tissue feedback with their surroundings to allow form acquisition. We also comment on how in silico models aid to integrate and predict changes in cell and tissue behaviour. Finally, considering recent advances from the developmental biomechanics field showing that mechanical inputs work as cues that promote morphogenesis, we invite to revisit the concept of morphogen.
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