Polymerase iota (Pol ι) prevents PrimPol-mediated nascent DNA synthesis and chromosome instability.

Recent studies have described a DNA damage tolerance pathway choice that involves a competition between PrimPol-mediated repriming and fork reversal. Screening different translesion DNA synthesis (TLS) polymerases by the use of tools for their depletion, we identified a unique role of Pol ι in regulating such a pathway choice. Pol ι deficiency unleashes PrimPol-dependent repriming, which accelerates DNA replication in a pathway that is epistatic with ZRANB3 knockdown. In Pol ι-depleted cells, the excess participation of PrimPol in nascent DNA elongation reduces replication stress signals, but thereby also checkpoint activation in S phase, triggering chromosome instability in M phase. This TLS-independent function of Pol ι requires its PCNA-interacting but not its polymerase domain. Our findings unravel an unanticipated role of Pol ι in protecting the genome stability of cells from detrimental changes in DNA replication dynamics caused by PrimPol.

Keyhole Endoscopic-Assisted Transcervical Approach to the Upper and Middle Retrostyloid Parapharyngeal Space: An Anatomic Feasibility Study.

Objectives The aim of this study was to describe the anatomical nuances, feasibility, limitations, and surgical exposure of the parapharyngeal space (PPS) through a novel minimally invasive keyhole endoscopic-assisted transcervical approach (MIKET). Design Descriptive cadaveric study. Setting Microscopic and endoscopic high-quality images were taken comparing the MIKET approach with a conventional combined transmastoid infralabyrinthine transcervical approach. Participants Five colored latex-injected specimens (10 sides). Main Outcome Measures Qualitative anatomical descriptions in four surgical stages; quantitative and semiquantitative evaluation of relevant landmarks. Results A 5 cm long inverted hockey stick incision was designed to access a corridor posterior to the parotid gland after independent mobilization of nuchal and cervical muscles to expose the retrostyloid PPS. The digastric branch of the facial nerve, which runs 16.5 mm over the anteromedial part of the posterior belly of the digastric muscle before piercing the parotid fascia, was used as a landmark to identify the main trunk of the facial nerve. MIKET corridor was superior to the crossing of the accessory nerve over the internal jugular vein within 17.3 mm from the jugular process. Further exposure of the occipital condyle, vertebral artery, and the jugular bulb was achieved. Conclusion The novel MIKET approach provides in the cadaver straightforward access to the upper and middle retrostyloid PPS through a natural corridor without injuring important neurovascular structures. Our work sets the anatomical nuances and limitations that should guide future clinical studies to prove its efficacy and safety either as a stand-alone procedure or as an adjunct to other approaches, such as the endonasal endoscopic approach.

CDK-Independent and PCNA-Dependent Functions of p21 in DNA Replication.

p21Waf/CIP1 is a small unstructured protein that binds and inactivates cyclin-dependent kinases (CDKs). To this end, p21 levels increase following the activation of the p53 tumor suppressor. CDK inhibition by p21 triggers cell-cycle arrest in the G1 and G2 phases of the cell cycle. In the absence of exogenous insults causing replication stress, only residual p21 levels are prevalent that are insufficient to inhibit CDKs. However, research from different laboratories has demonstrated that these residual p21 levels in the S phase control DNA replication speed and origin firing to preserve genomic stability. Such an S-phase function of p21 depends fully on its ability to displace partners from chromatin-bound proliferating cell nuclear antigen (PCNA). Vice versa, PCNA also regulates p21 by preventing its upregulation in the S phase, even in the context of robust p21 induction by irradiation. Such a tight regulation of p21 in the S phase unveils the potential that CDK-independent functions of p21 may have for the improvement of cancer treatments.

Unscheduled MRE11 activity triggers cell death but not chromosome instability in polymerase eta-depleted cells subjected to UV irradiation.

The elimination of DNA polymerase eta (pol η) causes discontinuous DNA elongation and fork stalling in UV-irradiated cells. Such alterations in DNA replication are followed by S-phase arrest, DNA double-strand break (DSB) accumulation, and cell death. However, their molecular triggers and the relative timing of these events have not been fully elucidated. Here, we report that DSBs accumulate relatively early after UV irradiation in pol η-depleted cells. Despite the availability of repair pathways, DSBs persist and chromosome instability (CIN) is not detectable. Later on cells with pan-nuclear γH2AX and massive exposure of template single-stranded DNA (ssDNA), which indicate severe replication stress, accumulate and such events are followed by cell death. Reinforcing the causal link between the accumulation of pan-nuclear ssDNA/γH2AX signals and cell death, downregulation of RPA increased both replication stress and the cell death of pol η-deficient cells. Remarkably, DSBs, pan-nuclear ssDNA/γH2AX, S-phase arrest, and cell death are all attenuated by MRE11 nuclease knockdown. Such results suggest that unscheduled MRE11-dependent activities at replicating DNA selectively trigger cell death, but not CIN. Together these results show that pol η-depletion promotes a type of cell death that may be attractive as a therapeutic tool because of the lack of CIN.

Lateral nasal wall flap for endoscopic reconstruction of the skull base: anatomical study and clinical series.

BACKGROUND: The lateral nasal wall (LNW) flap provides vascularized endonasal reconstruction primarily in revision surgery. Although the harvesting technique and reconstructive surface have been reported, the arterial supply to the LNW flap and its clinical implications is not well defined. This study presents anatomical dissections to clarify the vascular supply to this flap, and the associated clinical outcomes from this reconstructive technique. METHODS: The course and branching pattern of the sphenopalatine artery (SPA) to the LNW were studied in 6 vascular latex-injected heads (11 LNW flaps total). Patients undergoing an LNW flap since 2008 were identified and the underlying pathology, indication, flap viability, and clinical outcomes were retrospectively analyzed. RESULTS: The inferior turbinate artery arises from the LNW artery and divides into 2 branches at the most posterior aspect of the inferior turbinate bone. A smaller-caliber superficial branch travels anteriorly and branches to the LNW. A larger dominant branch travels into the inferior meatus and tangentially supplies the nasal floor. Twenty-four patients with sellar or posterior cranial fossa (PCF) defects were reconstructed with an LNW flap. Postoperative contrast enhancement of the LWN flap was identified in 95.5% of cases. Postoperative cerebrospinal fluid (CSF) leaks were identified in 6 cases. CONCLUSION: Blood supply to the nasal floor by the dominant inferior meatus branch is more robust than the supply to the anterior LNW by the superficial arterial branch. The LNW flap is the preferred vascularized reconstructive option to the PCF and sella in the absence of a nasoseptal flap (NSF).

Persistent double strand break accumulation does not precede cell death in an Olaparib-sensitive BRCA-deficient colorectal cancer cell model.

The poly (adenosine diphosphate (ADP)-ribosyl) polymerase inhibitors (PARPi) selectively kill cancer cells with BRCA1 or BRCA2 (BRCA)-mutations. It has been proposed that cell death induction after PARPi depends on unrepaired double strand breaks (DSBs) that accumulate due to the homologous recombination deficiency of BRCA-mutated cells. Such accumulation of DSBs is inferred mainly from the high levels of DNA damage markers like phosphorylated histone H2AX. Herein, we developed a model of isogenic cell lines to show that depletion of BRCA causes PARPi-triggered cell death, replication stress (phosphorylated-H2AX and 53BP1 foci), and genomic instability. However, persistent DSBs accumulation was not detected under the same experimental conditions. Hence, at least in this cellular model, the trigger for cell death in PARPi-treated BRCA-depleted samples is not the accumulation of unrepaired DSBs. Instead, cell death better correlates with a rapid and aberrant resolution of DSBs by error-prone pathways that leads to severe chromosomic aberrations. Therefore, our results suggest that in PARPi-treated BRCA-deficient cells, chromosome aberrations may dually trigger both genomic instability and cell death.

Meningioma petroclival. abordaje petroso combinado con extensión translaberíntica / Petroclival meningioma. petrosus approach combined with translabyrinthine extension

Objetivo: Presentar un caso de meningioma petroclival con extensión al cavum de Meckel, tratado quirúrgicamente a través de un abordaje petroso combinado con extensión translaberíntica. Introducción: Se define como meningioma petroclival, al que se origina en los dos tercios superiores de la fisura petroclival, y medial al nervio trigémino. Existen numerosos abordajes para estos tumores, y cada caso requiere un análisis individualizado. Descripción del caso: Paciente de 25 años que refiere cefalea de 6 meses de evolución, progresiva e invalidante, e hipoacusia derecha. Al examen físico presenta hipoestesia en territorio trigeminal derecho y desviación velopalatina a derecha. En la imagen de resonancia magnética (IRM) se evidencia voluminosa lesión expansiva petroclival derecha con extensión al cavum de Meckel. La cirugía fue programada en dos tiempos: en el primero se realizó el abordaje y en el segundo la exéresis tumoral total. En el post operatorio evolucionó con una hemiparesia izquierda transitoria y parálisis completa del tercer par derecho en recuperación. Discusión: Existen múltiples modalidades terapéuticas para los meningiomas de base de cráneo. En este caso considerando la ubicación, el tamaño, su extensión clival, al cavum de Meckel y su relación con la arteria basilar, se decidió realizar un abordaje petroso combinado, con extensión translaberíntica debido a la hipoacusia. Conclusiones: Los abordajes de base de cráneo acortan la distancia de trabajo al tumor y mejoran los ángulos de exposición, facilitando su exéresis. Su principal desventaja, que es el tiempo de realización, puede sortearse dividiendo la cirugía en 2 tiempos.

Objective: To present a patient with a right petroclival meningioma with extension into Meckel´s cave, surgically treated by combining a petrosal approach with translabyrinthine extension.Introduction: Petroclival meningiomas are tumors that arise from the upper two thirds of the petroclival fissure, medial to the trigeminal nerve. There are several treatment options, with every case warranting an individualized approach.Case description: Our patient was a 25-year-old male/female with a 6-month history of progressive, disabling headaches and right hearing loss. The physical exam revealed right trigeminal hypoesthesia and rightward deviation of the soft palate. Magnetic resonance imaging detected a huge right petroclival tumor with extension into Meckel´s cave. Two-stage surgery was planned, the first procedure to create an approach, and the second to attempt total tumor resection, which was achieved. Postoperatively, the patient had transient left hemiparesis and a complete third nerve palsy that recovered partially. Discussion: Many different surgical approaches exist for treating petroclival meningiomas. In this case, considering the tumor’s location and volume, its clival and Meckel´s cave extension and basilar artery involvement, we elected to combine a petrosal approach with translabyrinthine extension, due to the patient’s previous hearing loss. Conclusion: Skull-base approaches shorten the working distance to the tumor, improving the angle of approach and rendering total resection possible. One of the procedure’s main disadvantages is the time required; but this can be overcome by performing the procedure in two stages.