Decoding the Nucleolar Role in Meiotic Recombination and Cell Cycle Control: Insights into Cdc14 Function.

The cell cycle, essential for growth, reproduction, and genetic stability, is regulated by a complex network of cyclins, Cyclin-Dependent Kinases (CDKs), phosphatases, and checkpoints that ensure accurate cell division. CDKs and phosphatases are crucial for controlling cell cycle progression, with CDKs promoting it and phosphatases counteracting their activity to maintain balance. The nucleolus, as a biomolecular condensate, plays a key regulatory role by serving as a hub for ribosome biogenesis and the sequestration and release of various cell cycle regulators.

Analysis of Meiotic Progression by Ex Vivo Culture of Mouse Embryonic Ovaries.

Oogenesis is the central process required to produce viable oocytes in female mammals. It is initiated during embryonic development, and it involves the specification of primordial germ cells (PGCs) and progresses through the activation of the meiotic program, reaching a crucial phase in prophase I before pausing at diplotene around the time of birth. The significance of meiosis, particularly the prophase I stage, cannot be overstated, as it plays a pivotal role in ensuring the formation of healthy gametes, a prerequisite for successful reproduction.

SPO-Seq: An Accessible Method for Efficient Evaluation of Spo11 Catalytic Activity and Profiling Meiotic DSB Hotspots in Saccharomyces cerevisiae.

Meiotic recombination is a key process facilitating the formation of crossovers and the exchange of genetic material between homologous chromosomes in early meiosis. This involves controlled double-strand breaks (DSBs) formation catalyzed by Spo11. DSBs exhibit a preferential location in specific genomic regions referred to as hotspots, and their variability is tied to varying Spo11 activity levels.

Exportin-mediated nucleocytoplasmic transport maintains Pch2 homeostasis during meiosis.

The meiotic recombination checkpoint reinforces the order of events during meiotic prophase I, ensuring the accurate distribution of chromosomes to the gametes. The AAA+ ATPase Pch2 remodels the Hop1 axial protein enabling adequate levels of Hop1-T318 phosphorylation to support the ensuing checkpoint response. While these events are localized at chromosome axes, the checkpoint activating function of Pch2 relies on its cytoplasmic population.

The N-Terminal Region of the Polo Kinase Cdc5 Is Required for Downregulation of the Meiotic Recombination Checkpoint.

During meiosis, the budding yeast polo-like kinase Cdc5 is a crucial driver of the prophase I to meiosis I (G2/M) transition. The meiotic recombination checkpoint restrains cell cycle progression in response to defective recombination to ensure proper distribution of intact chromosomes to the gametes. This checkpoint detects unrepaired DSBs and initiates a signaling cascade that ultimately inhibits Ndt80, a transcription factor required for gene expression.

The Cdc14 Phosphatase Controls Resolution of Recombination Intermediates and Crossover Formation during Meiosis.

Meiotic defects derived from incorrect DNA repair during gametogenesis can lead to mutations, aneuploidies and infertility. The coordinated resolution of meiotic recombination intermediates is required for crossover formation, ultimately necessary for the accurate completion of both rounds of chromosome segregation. Numerous master kinases orchestrate the correct assembly and activity of the repair machinery.

Pch2 orchestrates the meiotic recombination checkpoint from the cytoplasm.

During meiosis, defects in critical events trigger checkpoint activation and restrict cell cycle progression. The budding yeast Pch2 AAA+ ATPase orchestrates the checkpoint response launched by synapsis deficiency; deletion of PCH2 or mutation of the ATPase catalytic sites suppress the meiotic block of the zip1Δ mutant lacking the central region of the synaptonemal complex. Pch2 action enables adequate levels of phosphorylation of the Hop1 axial component at threonine 318, which in turn promotes activation of the Mek1 effector kinase and the ensuing checkpoint response.

SWR1-Independent Association of H2A.Z to the LINC Complex Promotes Meiotic Chromosome Motion.

The H2A.Z histone variant is deposited into the chromatin by the SWR1 complex, affecting multiple aspects of meiosis. We describe here a SWR1-independent localization of H2A.

Characterization of Pch2 localization determinants reveals a nucleolar-independent role in the meiotic recombination checkpoint.

The meiotic recombination checkpoint blocks meiotic cell cycle progression in response to synapsis and/or recombination defects to prevent aberrant chromosome segregation. The evolutionarily conserved budding yeast Pch2 AAA+ ATPase participates in this pathway by supporting phosphorylation of the Hop1 adaptor at T318. In the wild type, Pch2 localizes to synapsed chromosomes and to the unsynapsed rDNA region (nucleolus), excluding Hop1.

Anterior Corneal Curvature and Aberration Changes After Scleral Lens Wear in Keratoconus Patients With and Without Ring Segments.

Objective: To evaluate changes in the anterior corneal curvature and aberrometry after scleral contact lens wear in keratoconus (KC) subjects with and without intracorneal ring segments (ICRS).

Methods: Twenty-six subjects diagnosed with keratoconus were selected to participate in the study. Subjects were divided into 2 groups, those with ICRS (KC-ICRS group) and those without ICRS (KC group).

Posterior cornea and thickness changes after scleral lens wear in keratoconus patients.

Purpose: To evaluate the changes in the corneal thickness, anterior chamber depth and posterior corneal curvature and aberrations after scleral lens wear in keratoconus patients with and without intrastromal corneal ring segments (ICRS).

Methods: Twenty-six keratoconus subjects (36.95 ± 8.

The influence of rigid gas permeable lens wear on the concentrations of dinucleotides in tears and the effect on dry eye signs and symptoms in keratoconus.

Purpose: To evaluate the signs and symptoms of dry eye and dinucleotide secretion in tears of keratoconus patients (KC) and the potential effect of rigid gas permeable (RGP) contact lens wear.

Methods: Twenty-three KC patients and forty control subjects were enrolled in this study. Signs of dry eye including tear volume, tear stability and corneal staining along with symptoms were assessed using the McMonnies questionnaire.

Essential and Checkpoint Functions of Budding Yeast ATM and ATR during Meiotic Prophase Are Facilitated by Differential Phosphorylation of a Meiotic Adaptor Protein, Hop1.

A hallmark of the conserved ATM/ATR signalling is its ability to mediate a wide range of functions utilizing only a limited number of adaptors and effector kinases. During meiosis, Tel1 and Mec1, the budding yeast ATM and ATR, respectively, rely on a meiotic adaptor protein Hop1, a 53BP1/Rad9 functional analog, and its associated kinase Mek1, a CHK2/Rad53-paralog, to mediate multiple functions: control of the formation and repair of programmed meiotic DNA double strand breaks, enforcement of inter-homolog bias, regulation of meiotic progression, and implementation of checkpoint responses. Here, we present evidence that the multi-functionality of the Tel1/Mec1-to-Hop1/Mek1 signalling depends on stepwise activation of Mek1 that is mediated by Tel1/Mec1 phosphorylation of two specific residues within Hop1: phosphorylation at the threonine 318 (T318) ensures the transient basal level Mek1 activation required for viable spore formation during unperturbed meiosis.

Ipl1/Aurora kinase suppresses S-CDK-driven spindle formation during prophase I to ensure chromosome integrity during meiosis.

Cells coordinate spindle formation with DNA repair and morphological modifications to chromosomes prior to their segregation to prevent cell division with damaged chromosomes. Here we uncover a novel and unexpected role for Aurora kinase in preventing the formation of spindles by Clb5-CDK (S-CDK) during meiotic prophase I and when the DDR is active in budding yeast. This is critical since S-CDK is essential for replication during premeiotic S-phase as well as double-strand break induction that facilitates meiotic recombination and, ultimately, chromosome segregation.

Clinical performance of a new hybrid contact lens for keratoconus.

Objectives: To compare the clinical performance of the Clearkone hybrid contact lens for the treatment of keratoconus against the habitual contact lens of the patients.

Methods: A total of 33 eyes from 18 patients were fitted with the Clearkone. High- and low-contrast visual acuity (HCVA and LCVA), central corneal thickness (CCT), and contrast sensitivity acuity (CSF) were recorded with habitual lenses (prestudy visit) and after 1 week, 15 days, and 1 month of wear of prescribed Clearkone.

Budding yeast ATM/ATR control meiotic double-strand break (DSB) levels by down-regulating Rec114, an essential component of the DSB-machinery.

An essential feature of meiosis is Spo11 catalysis of programmed DNA double strand breaks (DSBs). Evidence suggests that the number of DSBs generated per meiosis is genetically determined and that this ability to maintain a pre-determined DSB level, or "DSB homeostasis", might be a property of the meiotic program. Here, we present direct evidence that Rec114, an evolutionarily conserved essential component of the meiotic DSB-machinery, interacts with DSB hotspot DNA, and that Tel1 and Mec1, the budding yeast ATM and ATR, respectively, down-regulate Rec114 upon meiotic DSB formation through phosphorylation.

Changes in visual function under mesopic and photopic conditions after intrastromal corneal ring segment implantation for different stages of keratoconus.

Purpose: To analyze and compare the changes in visual function under mesopic and photopic conditions in different stages of keratoconus before and after Keraring intrastromal corneal ring segment (ICRS) implantation.

Setting: Clinico San Carlos Hospital and Faculty of Optics and Optometry, Complutense University, Madrid, Spain.

Design: Case series.

Recovery evaluation of induced changes in higher order aberrations from the anterior surface of the cornea for different pupil sizes after cessation of corneal refractive therapy.

Purpose: To assess corneal aberration changes induced by corneal refractive therapy (CRT) for different pupil sizes and to examine the recovery after cessation of contact lens wear.

Methods: A single-center, prospective, and longitudinal study was performed. Thirty-four subjects who underwent CRT for 1 year were included.

Phosphorylation of the axial element protein Hop1 by Mec1/Tel1 ensures meiotic interhomolog recombination.

An essential feature of meiosis is interhomolog recombination whereby a significant fraction of the programmed meiotic double-strand breaks (DSBs) is repaired using an intact homologous non-sister chromatid rather than a sister. Involvement of Mec1 and Tel1, the budding yeast homologs of the mammalian ATR and ATM kinases, in meiotic interhomlog bias has been implicated, but the mechanism remains elusive. Here, we demonstrate that Mec1 and Tel1 promote meiotic interhomolog recombination by targeting the axial element protein Hop1.

Meiotic roles of Mec1, a budding yeast homolog of mammalian ATR/ATM.

Budding yeast Mec1, a homolog of mammalian ATR/ATM, is an essential chromosome-based signal transduction protein. Mec1 is a key checkpoint regulator and plays a critical role in the maintenance of genome stability. Mec1 is also required for meiosis; loss of Mec1 functions leads to a number of meiotic defects including reduction in recombination, loss of inter-homolog bias, loss of crossover control, and failure in meiotic progression.

The G2 checkpoint activated by DNA damage does not prevent genome instability in plant cells.

Root growth, G2 length, and the frequency of aberrant mitoses and apoptotic nuclei were recorded after a single X-ray irradiation, ranging from 2.5 to 40 Gy, in Allium cepa L. root meristematic cells.

Transcription of ribosomal genes can cause nondisjunction.

Mitotic disjunction of the repetitive ribosomal DNA (rDNA) involves specialized segregation mechanisms dependent on the conserved phosphatase Cdc14. The reason behind this requirement is unknown. We show that rDNA segregation requires Cdc14 partly because of its physical length but most importantly because a fraction of ribosomal RNA (rRNA) genes are transcribed at very high rates.

DNA catenations that link sister chromatids until the onset of anaphase are maintained by a checkpoint mechanism.

Treatment of Allium cepa meristematic cells in metaphase with the topoisomerase II inhibitor ICRF-193, results in bridging of the sister chromatids at anaphase. Separation of the sisters in experimentally generated acentric chromosomal fragments was also inhibited by ICRF-193, indicating that some non-centromeric catenations also persist in metaphase chromosomes. Thus, catenations must be resolved by DNA topoisomerase II at the metaphase-to-anaphase transition to allow segregation of sisters.