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General Comment |
Animal Models for Studying the In Vivo Functions of Cell Cycle CDKs. Risal S et al. (2015) Multiple Cdks (Cdk4, Cdk6, and Cdk2) and a mitotic Cdk (Cdk1) are involved in cell cycle progression in mammals. Cyclins, Cdk inhibitors, and phosphorylations (both activating and inhibitory) at different cellular levels tightly modulate the activities of these kinases. Based on the results of biochemical studies, it was long believed that different Cdks functioned at specific stages during cell cycle progression. However, deletion of all three interphase Cdks in mice affected cell cycle entry and progression only in certain specialized cells such as hematopoietic cells, beta cells of the pancreas, pituitary lactotrophs, and cardiomyocytes. These genetic experiments challenged the prevailing biochemical model and established that Cdks function in a cell-specific, but not a stage-specific, manner during cell cycle entry and the progression of mitosis. Recent in vivo studies have further established that Cdk1 is the only Cdk that is both essential and sufficient for driving the resumption of meiosis during mouse oocyte maturation. These genetic studies suggest a minimal-essential cell cycle model in which Cdk1 is the central regulator of cell cycle progression. Cdk1 can compensate for the loss of the interphase Cdks by forming active complexes with A-, B-, E-, and D-type Cyclins in a stepwise manner. Thus, Cdk1 plays an essential role in both mitosis and meiosis in mammals, whereas interphase Cdks are dispensable.//////////////////
CDC2 is a catalytic subunit of a protein kinase complex, called the M-phase promoting factor, that induces entry into
mitosis and is universal among eukaryotes. In the fission yeast Schizosaccharomyces pombe, the gene cdc2 is
responsible for controlling the transition from G1 phase to the S phase and from the G2 phase to the M phase of the cell
cycle.Lincoln AJ, et al reported that Cdc25b phosphatase is required for resumption of meiosis during oocyte maturation.
In a wide variety of animal species, oocyte maturation is arrested temporarily at prophase of meiosis I . Resumption of meiosis requires activation of cyclin-dependent kinase-1 (CDK1, p34cdc2), one component of maturation-promoting factor (MPF). The dual specificity phosphatases Cdc25a, Cdc25b and Cdc25c are activators of cyclin-dependent kinases; consequently, they are postulated to regulate cell-cycle progression in meiosis and mitosis as well as the DNA-damage response. The authors generated Cdc25b-deficient (Cdc25b-/-) mice and found that they are viable. As compared with wildtype cells, fibroblasts from Cdc25b-/- mice grew vigorously in culture and arrested normally in response to DNA damage. Female Cdc25b-/- mice were sterile, and Cdc25b-/- oocytes remained arrested at prophase with low MPF activity. Microinjection of wildtype Cdc25b mRNA into Cdc25b-/- oocytes caused activation of MPF and resumption of meiosis. Thus, Cdc25b-/- female mice are sterile because of permanent meiotic arrest resulting from the inability to activate MPF. Cdc25b is therefore essential for meiotic resumption in female mice. Mice lacking Cdc25b provide the first genetic model for studying the mechanisms regulating prophase arrest in vertebrates.
oocyte maturation arrest at GV stage
NCBI Summary:
The protein encoded by this gene is a member of the Ser/Thr protein kinase family. This protein is a catalytic subunit of the highly conserved protein kinase complex known as M-phase promoting factor (MPF), which is essential for G1/S and G2/M phase transitions of eukaryotic cell cycle. Mitotic cyclins stably associate with this protein and function as regulatory subunits. The kinase activity of this protein is controlled by cyclin accumulation and destruction through the cell cycle. The phosphorylation and dephosphorylation of this protein also play important regulatory roles in cell cycle control. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Mar 2009]
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Comment |
First meiotic anaphase requires Cep55-dependent inhibitory Cdk1 phosphorylation. Zhou C et al. (2019) During mitosis, anaphase is triggered by anaphase-promoting complex (APC)-mediated destruction of securin and cyclin B1, which leads to inactivation of cyclin-dependent kinase 1 (Cdk1). By regulating APC activity, the mitotic spindle assembly checkpoint (SAC) therefore has robust control over anaphase-timing to prevent chromosome mis-segregation. Mammalian oocytes are prone to aneuploidy, the reasons for which, remain obscure. Here, in mouse oocytes, we deplete Cep55, which, in mitosis, is required post-anaphase for the final steps of cytokinesis. We find that Cep55-depleted oocytes progress normally through early meiosis I, but that anaphase I fails due to persistent Cdk1 activity. Unexpectedly, compromised Cdk1 inactivation following Cep55-depletion occurred despite on-time SAC silencing and intact APC-mediated proteolysis. Instead, it was due to inadequate inhibitory Cdk1 phosphorylation consequent upon failure to suppress Cdc25 phosphatase, identifying a proteolysis-independent step necessary for anaphase I. Thus, the SAC in oocytes does not exert exclusive control over anaphase I-initiation, providing new insight into vulnerability to error.//////////////////
Cdk1 inactivation induces post-anaphase-onset spindle migration and membrane protrusion required for extreme asymmetry in mouse oocytes. Wei Z et al. (2018) Female meiotic divisions are extremely asymmetric, producing large oocytes and small polar bodies (PBs). In mouse oocytes, the spindle relocates to the cortex before anaphase of meiosis I (MI). It is presumed that by displacing the future midzone, pre-anaphase spindle repositioning alone ensures asymmetry. But how subsequent anaphase events might contribute to asymmetric PB extrusion (PBE) is unknown. Here, we find that inactivation of cyclin-dependent kinase 1 (Cdk1) induces anaphase and simultaneously triggers cytoplasmic formin-mediated F-actin polymerisation that propels the spindle into the cortex causing it to protrude while anaphase progresses. Significantly, if post-anaphase-onset spindle migration fails, protrusion and asymmetry are severely threatened even with intact pre-anaphase migration. Conversely, post-anaphase migration can completely compensate for failed pre-anaphase migration. These data identify a cell-cycle-triggered phase of spindle displacement occurring after anaphase-onset, which, by inducing protrusion, is necessary for extreme asymmetry in mouse oocytes and uncover a pathway for maximising unequal division.//////////////////
A cdk1 gradient guides surface contraction waves in oocytes. Bischof J et al. (2017) Surface contraction waves (SCWs) in oocytes and embryos lead to large-scale shape changes coupled to cell cycle transitions and are spatially coordinated with the cell axis. Here, we show that SCWs in the starfish oocyte are generated by a traveling band of myosin II-driven cortical contractility. At the front of the band, contractility is activated by removal of cdk1 inhibition of the RhoA/RhoA kinase/myosin II signaling module, while at the rear, contractility is switched off by negative feedback originating downstream of RhoA kinase. The SCW's directionality and speed are controlled by a spatiotemporal gradient of cdk1-cyclinB. This gradient is formed by the release of cdk1-cyclinB from the asymmetrically located nucleus, and progressive degradation of cyclinB. By combining quantitative imaging, biochemical and mechanical perturbations with mathematical modeling, we demonstrate that the SCWs result from the spatiotemporal integration of two conserved regulatory modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.Surface contraction waves (SCWs) are prominent shape changes coupled to cell cycle transitions in oocytes. Here the authors show that SCWs are patterned by the spatiotemporal integration of two conserved modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.//////////////////
Nicotinamide impairs entry into and exit from meiosis I in mouse oocytes. Riepsamen A et al. (2015) Following exit from meiosis I, mammalian oocytes immediately enter meiosis II without an intervening interphase, accompanied by rapid reassembly of a bipolar spindle that maintains condensed chromosomes in a metaphase configuration (metaphase II arrest). Here we study the effect of nicotinamide (NAM), a non-competitive pan-sirtuin inhibitor, during meiotic maturation in mouse oocytes. Sirtuins are a family of seven NAD+-dependent deacetylases (Sirt1-7), which are involved in multiple cellular processes and are emerging as important regulators in oocytes and embryos. We found that NAM significantly delayed entry into meiosis I associated with delayed accumulation of the Cdk1 co-activator, cyclin B1. GVBD was also inhibited by the Sirt2-specific inhibitor, AGK2, and in a very similar pattern to NAM, supporting the notion that as in somatic cells, NAM inhibits sirtuins in oocytes. NAM did not affect subsequent spindle assembly, chromosome alignment or the timing of first polar body extrusion (PBE). Unexpectedly, however, in the majority of oocytes with a polar body, chromatin was decondensed and a nuclear structure was present. An identical phenotype was observed when flavopiridol was used to induce Cdk1 inactivation during late meiosis I prior to PBE, but not if Cdk1 was inactivated after PBE when metaphase II arrest was already established, altogether indicating that NAM impaired establishment rather than maintenance of metaphase II arrest. During meiosis I exit in NAM-treated medium, we found that cyclin B1 levels were lower and inhibitory Cdk1 phosphorylation was increased compared with controls. Although activation of the anaphase-promoting complex-Cdc20 (APC-Cdc20) occurred on-time in NAM-treated oocytes, Cdc20 levels were higher in very late meiosis I, pointing to exaggerated APC-Cdc20-mediated proteolysis as a reason for lower cyclin B1 levels. Collectively, therefore, our data indicate that by disrupting Cdk1 regulation, NAM impairs entry into meiosis I and the establishment of metaphase II arrest.//////////////////
Dual-mode regulation of the APC/C by CDK1 and MAPK controls meiosis I progression and fidelity. Nabti I 2014 et al.
Female meiosis is driven by the activities of two major kinases, cyclin-dependent kinase 1 (Cdk1) and mitogen-activated protein kinase (MAPK). To date, the role of MAPK in control of meiosis is thought to be restricted to maintaining metaphase II arrest through stabilizing Cdk1 activity. In this paper, we find that MAPK and Cdk1 play compensatory roles to suppress the anaphase-promoting complex/cyclosome (APC/C) activity early in prometaphase, thereby allowing accumulation of APC/C substrates essential for meiosis I. Furthermore, inhibition of MAPK around the onset of APC/C activity at the transition from meiosis I to meiosis II led to accelerated completion of meiosis I and an increase in aneuploidy at metaphase II. These effects appear to be mediated via a Cdk1/MAPK-dependent stabilization of the spindle assembly checkpoint, which when inhibited leads to increased APC/C activity. These findings demonstrate new roles for MAPK in the regulation of meiosis in mammalian oocytes.
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Dependency of the Spindle Assembly Checkpoint on Cdk1 Renders the Anaphase Transition Irreversible. Rattani A 2014 et al.
Activation of anaphase-promoting complex/cyclosome (APC/C(Cdc20)) by Cdc20 is delayed by the spindle assembly checkpoint (SAC). When all kinetochores come under tension, the SAC is turned off and APC/C(Cdc20) degrades cyclin B and securin, which activates separase 1]. The latter then cleaves cohesin holding sister chromatids together [2]. Because cohesin cleavage also destroys the tension responsible for turning off the SAC, cells must possess a mechanism to prevent SAC reactivation during anaphase, which could be conferred by a dependence of the SAC on Cdk1 [3-5]. To test this, we analyzed mouse oocytes and embryos expressing nondegradable cyclin B together with a Cdk1-resistant form of separase. After biorientation and SAC inactivation, APC/C(Cdc20) activates separase but the resulting loss of (some) cohesion is accompanied by SAC reactivation and APC/C(Cdc20) inhibition, which aborts the process of further securin degradation. Cyclin B is therefore the only APC/C(Cdc20) substrate whose degradation at the onset of anaphase is necessary to prevent SAC reactivation. The mutual activation of tension sensitive SAC and Cdk1 creates a bistable system that ensures complete activation of separase and total downregulation of Cdk1 when all chromosomes have bioriented.
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A specific inhibitor of CDK1, RO-3306, reversibly arrests meiosis during in vitro maturation of porcine oocytes. [Jang WI 2013 et al.
CDK1 plays pivotal role in meiotic progression of oocytes from G2 to metaphase II (MII) stage. In this study, we investigated the possibility of utilizing a selective inhibitor of CDK1, RO-3306, as a novel agent for the synchronization of oocyte maturation. Two groups of cumulus-oocyte complexes (COCs) were treated with 10?M RO-3306. The first group was treated for 44h, whereas the second group was transferred to drug-free medium after a 20h treatment. MII-stage oocytes from each group were confirmed by cytoplasmic maturation and embryonic development assays. Treatment of immature porcine oocytes with RO-3306 for 20h arrested them at the germinal vesicle (GV) stage. The GV-arrest effect of RO-3306 was reversible: when RO-3306-arrested COCs were subsequently cultured for 24h in the absence of RO-3306, 76.19?2.68% of these oocytes reached the MII stage after 44h of in vitro maturation, a rate similar to that of non-treated control oocytes (79.08?3.23%). Furthermore, RO-3306-treated oocytes transferred to drug-free media did not differ significantly from controls (P>0.05) with respect to cleavage and blastocyst formation upon parthenogenetic activation. To explore the underlying molecular mechanisms, we examined the expression patterns of four representative maternal transcripts, CDK1, Cyclin B1, GDF9, and BMP15, by real-time polymerase chain reaction (PCR) and poly(A)-test PCR (PAT assay). RO-3306 treatment increased expression of CDK1 but had no effect on the expression of the other genes. These data suggest that RO-3306 efficiently blocks and synchronizes the meiotic progression of porcine oocytes at the GV stage without affecting their meiotic and cytoplasmic maturation.
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Increased CDK1 activity determines the timing of kinetochore-microtubule attachments in meiosis I. Davydenko O 2013 et al.
Chromosome segregation during cell division depends on stable attachment of kinetochores to spindle microtubules. Mitotic spindle formation and kinetochore-microtubule (K-MT) capture typically occur within minutes of nuclear envelope breakdown. In contrast, during meiosis I in mouse oocytes, formation of the acentrosomal bipolar spindle takes 3-4 h, and stabilization of K-MT attachments is delayed an additional 3-4 h. The mechanism responsible for this delay, which likely prevents stabilization of erroneous attachments during spindle formation, is unknown. Here we show that during meiosis I, attachments are regulated by CDK1 activity, which gradually increases through prometaphase and metaphase I. Partial reduction of CDK1 activity delayed formation of stable attachments, whereas a premature increase in CDK1 activity led to precocious formation of stable attachments and eventually lagging chromosomes at anaphase I. These results indicate that the slow increase in CDK1 activity in meiosis I acts as a timing mechanism to allow stable K-MT attachments only after bipolar spindle formation, thus preventing attachment errors.
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Cdc25B phosphatase participates in maintaining metaphase II arrest in mouse oocytes. Kang H et al. Cdc25B is an essential regulator for meiotic resumption in mouse oocytes. However, the role of this phosphatase during the later stage of the meiotic cell cycle is not known. In this study, we investigated the role of Cdc25B during metaphase II (MII) arrest in mouse oocytes. Cdc25B was extensively phosphorylated during MII arrest with an increase in the phosphatase activity toward Cdk1. Downregulation of Cdc25B by antibody injection induced the formation of a pronucleus-like structure. Conversely, overexpression of Cdc25B inhibited Ca(2+)-mediated release from MII arrest. Moreover, Cdc25B was immediately dephosphorylated and hence inactivated during MII exit, suggesting that Cdk1 phosphorylation is required to exit from MII arrest. Interestingly, this inactivation occurred prior to cyclin B degradation. Taken together, our data demonstrate that MII arrest in mouse oocytes is tightly regulated not only by the proteolytic degradation of cyclin B but also by dynamic phosphorylation of Cdk1.
Greatwall kinase and cyclin B-Cdk1 are both critical constituents of M-phase-promoting factor. Hara M et al. Maturation/M-phase-promoting factor is the universal inducer of M-phase in eukaryotic cells. It is currently accepted that M-phase-promoting factor is identical to the kinase cyclin B-Cdk1. Here we show that cyclin B-Cdk1 and M-phase-promoting factor are not in fact synonymous. Instead, M-phase-promoting factor contains at least two essential components: cyclin B-Cdk1 and another kinase, Greatwall kinase. In the absence of Greatwall kinase, the M-phase-promoting factor is undetectable in oocyte cytoplasm even though cyclin B-Cdk1 is fully active, whereas M-phase-promoting factor activity is restored when Greatwall kinase is added back. Although the excess amount of cyclin B-Cdk1 alone, but not Greatwall kinase alone, can induce nuclear envelope breakdown, spindle assembly is abortive. Addition of Greatwall kinase greatly reduces the amount of cyclin B-Cdk1 required for nuclear envelope breakdown, resulting in formation of the spindle with aligned chromosomes. M-phase-promoting factor is thus a system consisting of one kinase (cyclin B-Cdk1) that directs mitotic entry and a second kinase (Greatwall kinase) that suppresses the protein phosphatase 2A-B55 which opposes cyclin B-Cdk1.
From ubiquitin-proteasomal degradation to CDK1 inactivation: requirements for the first polar body extrusion in mouse oocytes. Pomerantz Y et al. Completion of the first meiotic division, manifested by extrusion of the first polar body (PBI), depends on proteasomal degradation of cyclin B1 and securin and the subsequent respective CDK1 inactivation and chromosome segregation. We aimed at identifying the polyubiquitin signal that mediates proteasomal action and at a better characterization of the role of CDK1 inactivation at this stage of meiosis. Microinjections of mutated ubiquitin proteins into mouse oocytes revealed that interference with lysine-11 polyubiquitin chains abrogated chromosome segregation and reduced PBI extrusion by 63% as compared to WT ubiquitin-injected controls. Inactivation of CDK1 in oocytes arrested at first metaphase by a proteasome inhibitor fully rescued PBI extrusion. However, removal of CDK1 inhibition failed to allow progression to the second metaphase, rather, inducing PBI reengulfment in 62% of the oocytes. Inhibition of either PLK1 or MEK1/2 during the first anaphase changed spindle dimensions. The PLK1 inhibitor also blocked PBI emission and prevented RhoA translocation. Our results identified lysine-11 rather than the canonic lysine-48 ubiquitin chains as the degradation signal in oocytes resuming meiosis, further disclosing that CDK1 inactivation is necessary and sufficient for PBI emission. This information significantly contributes to our understanding of faulty chromosome segregation that may lead to aneuploidy.-Pomerantz, Y., Elbaz, J., Ben-Eliezer, I., Reizel, Y., David, Y., Galiani, D., Nevo, N., Navon, A., Dekel, N. From ubiquitin-proteasomal degradation to CDK1 inactivation: requirements for the first polar body extrusion in mouse oocytes.
Shimada M et al 2001 reported the inhibition of phosphatidylinositol 3-kinase or mitogen-activated
protein kinase kinase leads to suppression of p34(cdc2) kinase
activity and meiotic progression beyond the meiosis I stage in
porcine oocytes surrounded with cumulus cells. These
results suggest that increasing MAP kinase activity in oocytes via the PI 3-kinase
signaling pathway in cumulus cells is involved in the stimulation of maturation
promoting factor, leading to meiotic progression beyond the MI to MII stage in
porcine oocytes.
Motlik J, et al reported
that co-culture with pig membrana granulosa cells modulates the activity of cdc2 and
MAP kinase in maturing cattle oocytes.
Expression of wee1 and its related cell cycle components in mouse early stage follicles
Park CE, et al .
Wee1 is a kinase regulator of the M-phase promoting factor (a complex of cdc2 and cyclin B1). The present study was performed to determine the role(s) of wee1 in the early stages of mouse ovarian follicles. Expression of wee1 and the correlated cell cycle components, namely cdc2, cyclin B1, and cdc25C, was evaluated by immunohistochemistry. In addition, expression of Tyr15-phosphorylated cdc2 (cdc2-p) was also examined to determine whether wee1 kinase phosphorylates cdc2. Each component except cdc25C was found in the oocyte cytoplasm at all follicular stages, while cdc25C was not detected in primordial follicles. It was found primarily in ovarian interstitial cells and to a small extent in granulosa cells of the developing secondary follicles. To further confirm the expression of cell cycle components in the primordial follicular oocytes, day 1 ovaries were enzymatically and mechanically dissociated, then oocytes were isolated from somatic cells including pre-granulosa cells, and we confirmed that cdc2-p was expressed in oocytes of primordial follicles. The results of the present study led to the conclusion that wee1, without the counteracting cdc25C, would cause meiotic arrest of oocytes by inhibitory phosphorylation of cdc2. Expression of all these proteins in the granulosa cells of growing follicles may regulate granulosa cell mitosis concurrently with the growth of oocytes and follicles.
Histone H1 kinase activity, germinal vesicle breakdown and M phase entry in mouse oocytes. Gavin AC et al. Meiotic reinitiation of the mouse oocyte is characterized by a slow entry into metaphase I, beginning with germinal vesicle breakdown and ending with spindle formation. It is accompanied by a cascade of protein kinases and phosphatases increasing protein phosphorylation. The activation of histone H1 kinase and that of the mitogen-activated protein kinase p42 have been compared during spontaneous or okadaic acid-induced meiotic reinitiation. In spontaneously maturing oocytes, histone H1 kinase activity increases before germinal vesicle breakdown (2-fold), in a protein synthesis-independent manner. It is associated with the disappearance of the upper migrating form of p34cdc2, which, in our system, seems to represent the tyrosine phosphorylated form. Following germinal vesicle breakdown, histone H1 kinase activity culminates (8-fold) in metaphase I and requires protein synthesis. Activation by phosphorylation of p42MAPK is observed as a permanent shift upward-migrating form and by its myelin basic protein kinase activity. It occurs after germinal vesicle breakdown and depends on protein synthesis. In contrast, no increase of histone H1 kinase is detectable in oocytes induced to reinitiate meiosis by a transient inhibition of okadaic acid-sensitive phosphatase(s), either before germinal vesicle breakdown or during the following 7 hours of culture. A slight increase is nevertheless evident after 17 hours, when oocytes are arrested with an abnormal metaphase I spindle. The upper migrating form of p34cdc2 is present for 8 hours. The activation of p42MAPK begins before germinal vesicle breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)
Essential CDK1-inhibitory role for separase during meiosis I in vertebrate oocytes. Gorr IH et al. Separase not only triggers anaphase of meiosis I by proteolytic cleavage of cohesin on chromosome arms, but in vitro vertebrate separase also acts as a direct inhibitor of cyclin-dependent kinase 1 (Cdk1) on liberation from the inhibitory protein, securin. Blocking separase-Cdk1 complex formation by microinjection of anti-separase antibodies prevents polar-body extrusion in vertebrate oocytes. Importantly, proper meiotic maturation is rescued by chemical inhibition of Cdk1 or expression of Cdk1-binding separase fragments lacking cohesin-cleaving activity.
Constant regulation of both the MPF amplification loop and the Greatwall-PP2A pathway is required for metaphase II arrest and correct entry into the first embryonic cell cycle. Lorca T et al. Recent results indicate that regulating the balance between cyclin-B-Cdc2 kinase, also known as M-phase-promoting factor (MPF), and protein phosphatase 2A (PP2A) is crucial to enable correct mitotic entry and exit. In this work, we studied the regulatory mechanisms controlling the cyclin-B-Cdc2 and PP2A balance by analysing the activity of the Greatwall kinase and PP2A, and the different components of the MPF amplification loop (Myt1, Wee1, Cdc25) during the first embryonic cell cycle. Previous data indicated that the Myt1-Wee1-Cdc25 equilibrium is tightly regulated at the G2-M and M-G1 phase transitions; however, no data exist regarding the regulation of this balance during M phase and interphase. Here, we demonstrate that constant regulation of the cyclin-B-Cdc2 amplification loop is required for correct mitotic division and to promote correct timing of mitotic entry. Our results show that removal of Cdc25 from metaphase-II-arrested oocytes promotes mitotic exit, whereas depletion of either Myt1 or Wee1 in interphase egg extracts induces premature mitotic entry. We also provide evidence that, besides the cyclin-B-Cdc2 amplification loop, the Greatwall-PP2A pathway must also be tightly regulated to promote correct first embryonic cell division. When PP2A is prematurely inhibited in the absence of cyclin-B-Cdc2 activation, endogenous cyclin-A-Cdc2 activity induces irreversible aberrant mitosis in which there is, first, partial transient phosphorylation of mitotic substrates and, second, subsequent rapid and complete degradation of cyclin A and cyclin B, thus promoting premature and rapid exit from mitosis.
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Mutations |
3 mutations
Species: mouse
Mutation name: None
type: null mutation
fertility: embryonic lethal
Comment: Prescribing pattern in a Dutch university hospital. Denig P et al. In many countries, including The Netherlands, little is known about the overall prescribing patterns within hospitals. While individual hospitals have some data available, these are not pooled on a regional or national level. The available data consist of dispensing data that are neither patient-linked nor diagnosis-linked. We report the results of a study in a Dutch university hospital which show that despite the limitations, such data can be used for a general evaluation of prescribing patterns. Using three categories of undesirable or irrational drug prescribing the dispensing data were screened. The categories were 'inferior or dubious' drugs, 'semi-innovative' drugs, and 'inappropriately used' drugs. The results show that most problems are seen with the use of new drugs. In the first instance, this involves the use of semi-innovative drugs whose adoption may be stimulated by clinical trials in the hospital concerned. Secondly, innovative drugs seem to be used on too large a scale, i.e., for indications for which their use is not warranted. Based on these findings, a follow-up study has been initiated to study some of these suboptimal drug choices in detail.
Species: mouse
Mutation name: None
type: null mutation
fertility: infertile - ovarian defect
Comment: Cdk1, but not Cdk2, is the sole Cdk that is essential and sufficient to drive resumption of meiosis in mouse oocytes. Adhikari D et al. Mammalian oocytes are arrested at the prophase of meiosis I during fetal or postnatal development, and the meiosis is resumed by the preovulatory surge of luteinizing hormone. The in vivo functional roles of cyclin-dependent kinases (Cdks) during the resumption of meiosis in mammalian oocytes are largely unknown. Previous studies have shown that deletions of Cdk3, Cdk4 or Cdk6 in mice result in viable animals with normal oocyte maturation, indicating that these Cdks are not essential for the meiotic maturation of oocytes. In addition, conventional knockout of Cdk1 and Cdk2 leads to embryonic lethality and postnatal follicular depletion, respectively, making it impossible to study the functions of Cdk1 and Cdk2 in oocyte meiosis. In this study, we generated conditional knockout mice with oocyte-specific deletions of Cdk1 and Cdk2. We showed that the lack of Cdk1, but not of Cdk2, leads to female infertility due to a failure of the resumption of meiosis in the oocyte. Re-introduction of Cdk1 mRNA into Cdk1-null oocytes largely resumed meiosis. Thus, Cdk1 is the sole Cdk that is essential and sufficient to drive resumption of meiosis in mouse oocytes. We also found that Cdk1 maintains the phosphorylation status of protein phosphatase 1 and lamin A/C in oocytes in order for meiosis resumption to occur.
Species: mouse
Mutation name:
type: null mutation
fertility: infertile - ovarian defect
Comment: Inhibitory phosphorylation of Cdk1 mediates prolonged prophase I arrest in female germ cells and is essential for female reproductive lifespan. Adhikari D et al. (2016) A unique feature of female germ cell development in mammals is their remarkably long arrest at the prophase of meiosis I, which lasts up to 50 years in humans. Both dormant and growing oocytes are arrested at prophase I and completely lack the ability to resume meiosis. Here, we show that the prolonged meiotic arrest of female germ cells is largely achieved via the inhibitory phosphorylation of Cdk1 (cyclin-dependent kinase 1). In two mouse models where we have introduced mutant Cdk1(T14AY15F) which cannot be inhibited by phosphorylation (Cdk1AF) in small meiotically incompetent oocytes, the prophase I arrest is interrupted, leading to a premature loss of female germ cells. We show that in growing oocytes, Cdk1AF leads to premature resumption of meiosis with condensed chromosomes and germinal vesicle breakdown followed by oocyte death, whereas in dormant oocytes, Cdk1AF leads to oocyte death directly, and both situations damage the ovarian reserve that maintains the female reproductive lifespan, which should be around 1 year in mice. Furthermore, interruption of the inhibitory phosphorylation of Cdk1 results in DNA damage, which is accompanied by induction of the Chk2 (checkpoint kinase 2)-p53/p63-dependent cell death pathway, which eventually causes global oocyte death. Together, our data demonstrate that the phosphorylation-mediated suppression of Cdk1 activity is one of the crucial factors that maintain the lengthy prophase arrest in mammalian female germ cells, which is essential for preserving the germ cell pool and reproductive lifespan in female mammals.//////////////////
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