CDK4/6 activity is required during G2 arrest to prevent stress-induced endoreplication

Cell cycle events are coordinated by cyclin-dependent kinases (CDKs) to ensure robust cell division. CDK4/6 and CDK2 regulate the growth 1 (G1) to synthesis (S) phase transition of the cell cycle by responding to mitogen signaling, promoting E2F transcription and inhibition of the anaphase-promoting complex. We found that this mechanism was still required in G2-arrested cells to prevent cell cycle exit after the S phase. This mechanism revealed a role for CDK4/6 in maintaining the G2 state, challenging the notion that the cell cycle is irreversible and that cells do not require mitogens after passing the restriction point. Exit from G2 occurred during ribotoxic stress and was actively mediated by stress-activated protein kinases. Upon relief of stress, a significant fraction of cells underwent a second round of DNA replication that led to whole-genome doubling.

Sustained ERK signaling promotes G2 cell cycle exit and primes cells for whole-genome duplication

Whole-genome duplication (WGD) is a frequent event in cancer evolution that fuels chromosomal instability. WGD can result from mitotic errors or endoreduplication, yet the molecular mechanisms that drive WGD remain unclear. Here, we use live single-cell analysis to characterize cell-cycle dynamics upon aberrant Ras-ERK signaling. We find that sustained ERK signaling in human cells leads to reactivation of the APC/C in G2, resulting in tetraploid G0-like cells that are primed for WGD. This process is independent of DNA damage or p53 but dependent on p21. Transcriptomics analysis and live-cell imaging showed that constitutive ERK activity promotes p21 expression, which is necessary and sufficient to inhibit CDK activity and which prematurely activates the anaphase-promoting complex (APC/C). Finally, either loss of p53 or reduced ERK signaling allowed for endoreduplication, completing a WGD event. Thus, sustained ERK signaling-induced G2 cell cycle exit represents an alternative path to WGD.

Iatrogenic haemoperitoneum requiring transfusion after ventriculoperitoneal shunt placement: case report

Cerebrospinal fluid (CSF) diversion for hydrocephalus via ventriculoperitoneal (VP) shunting is one of the most commonly performed neurosurgical procedures. Unfortunately, VP shunting also carries a high complication rate. While long-term complications of VP shunting are generally well-described, the literature on more acute, iatrogenic injury during shunt placement is essentially limited to easily identifiable intracranial bleeds. Herein is presented the first reported case of iatrogenic abdominal wall vessel injury as a consequence of blind distal VP shunt catheter placement causing a critical haemoperitoneum that necessitated multiple transfusions. Presentation and recognition of this bleed was delayed as it occurred over a number of days. Injury to the inferior epigastric artery, or potentially a distal branch of the superficial epigastric artery, is suspected to have occurred during either blind subcutaneous tunnelling of the shunt catheter passage or during penetration of the peritoneum. Haemoperitoneum as a potential complication of procedures involving manipulation or penetration of the abdominal wall (i.e. paracentesis) is well-described in the medical and general surgical literature, and ultrasound-guidance has been widely adopted to mitigate bleeding in these cases. Familiarity with intra-abdominal haemorrhage as a potential complication of VP shunting and an understanding of its presentation is critical for timely identification of this phenomenon. Furthermore, the use of real-time ultrasound-guidance for tunnelling and distal shunt catheter placement may decrease the incidence of intrabdominal complications after shunt placement more generally and should be considered an area of future study.

A subclass of evening cells promotes the switch from arousal to sleep at dusk

Animals exhibit rhythmic patterns of behavior that are shaped by an internal circadian clock and the external environment. While light intensity varies across the day, there are particularly robust differences at twilight (dawn/dusk). These periods are also associated with major changes in behavioral states, such as the transition from arousal to sleep. However, the neural mechanisms by which time and environmental conditions promote these behavioral transitions are poorly defined. Here, we show that the E1 subclass of Drosophila evening clock neurons promotes the transition from arousal to sleep at dusk. We first demonstrate that the cell-autonomous clocks of E2 neurons alone are required to drive and adjust the phase of evening anticipation, the canonical behavior associated with "evening" clock neurons. We next show that conditionally silencing E1 neurons causes a significant delay in sleep onset after dusk. However, rather than simply promoting sleep, activating E1 neurons produces time- and light- dependent effects on behavior. Activation of E1 neurons has no effect early in the day, but then triggers arousal before dusk and induces sleep after dusk. Strikingly, these phenotypes critically depend on the presence of light during the day. Despite their influence on behavior around dusk, in vivo voltage imaging of E1 neurons reveals that their spiking rate does not vary between dawn and dusk. Moreover, E1-specific clock ablation has no effect on arousal or sleep. Thus, we suggest that, rather than specifying "evening" time, E1 neurons act, in concert with other rhythmic neurons, to promote behavioral transitions at dusk.