The CRL4DTL E3 ligase induces degradation of the DNA replication initiation factor TICRR/TRESLIN specifically during S phase.

A DNA replication program, which ensures that the genome is accurately and wholly replicated, is established during G1, before the onset of S phase. In G1, replication origins are licensed, and upon S phase entry, a subset of these will form active replisomes. Tight regulation of the number of active replisomes is crucial to prevent replication stress-induced DNA damage. TICRR/TRESLIN is essential for DNA replication initiation, and the level of TICRR and its phosphorylation determine the number of origins that initiate during S phase. However, the mechanisms regulating TICRR protein levels are unknown. Therefore, we set out to define the TICRR/TRESLIN protein dynamics throughout the cell cycle. Here, we show that TICRR levels are high during G1 and dramatically decrease as cells enter S phase and begin DNA replication. We show that degradation of TICRR occurs specifically during S phase and depends on ubiquitin ligases and proteasomal degradation. Using two targeted siRNA screens, we identify CRL4DTL as a cullin complex necessary for TICRR degradation. We propose that this mechanism moderates the level of TICRR protein available for replication initiation, ensuring the proper number of active origins as cells progress through S phase.

Cell Cycle-Dependent TICRR/TRESLIN and MTBP Chromatin Binding Mechanisms and Patterns.

The selection of replication origins is a defining characteristic of DNA replication in eukaryotes, yet its mechanism in humans has not been well-defined. In this study, we use Cut&Run to examine genomic binding locations for TICRR/TRESLIN and MTBP, the human orthologs for the yeast DNA replication initiation factors Sld3 and Sld7. We mapped TRESLIN and MTBP binding in HCT116 colorectal cancer cells using asynchronous and G1 synchronized populations. Our data show that TRESLIN and MTBP binding patterns are more defined in a G1 synchronized population compared to asynchronously cycling cells. We also examined whether TRESLIN and MTBP are dependent on one another for binding. Our data suggest MTBP is dependent on TRESLIN for proper association with chromatin during G1 but not S phase. Finally, we asked whether TRESLIN and MTBP binding to chromatin requires licensed origins. Using cell lines with a non-degradable inducible Geminin to inhibit licensing, we show TRESLIN and MTBP binding does not require loaded MCMs. Altogether, our Cut&Run data provides evidence for a chromatin binding mechanism of TRESLIN-MTBP during G1 that is dependent on TRESLIN and does not require interactions with licensed origins.

A Narrative Analysis of the Progression in the Top 100 Marathon, Half-Marathon, and 10-km Road Race Times from 2001 to 2019.

PURPOSE: This study aimed to characterize and describe finishing time trends of the fastest 100 performers in the men's and women's marathon, half-marathon, and road 10-km each year from 2001 to 2019 and assess the underlying basis for recent performance improvements. METHODS: The top 100 performers for each sex, event, and year were partitioned into four arbitrary ranking groups: 1-10, 11-25, 26-50, and 51-100. The percent improvement in mean performance time for each year beyond 2001 was calculated for each ranking group, event, and sex. Multiple linear regression was also used to determine improvement trend for each ranking group, both sexes, and all events for each 3-yr period between Olympic years. RESULTS: In total, 11,400 performances in the marathon, half-marathon, and 10-km road races from 2001 to 2019 were analyzed. The 3-yr period preceding the original date of the Tokyo Olympics (2017-2019) accounted for 44% and 35% of the overall improvement in marathon time from 2001 to 2019 for women and men, respectively. The years 2017-2019 featured the largest average improvement of any 3-yr period and was the only period where nearly every ranking group in every event for both sexes improved. CONCLUSIONS: The results suggest that recent world record performances are a result of overall circumstances affecting road racing (e.g., shoe technology) rather than the outstanding physiology of individual top runners, per se.

Marathon Specialization in Elites: A Head Start for Africans.

PURPOSE: To assess differences in event-specific specialization between elite African and non-African male marathon runners based on age, performance, and career length. METHODS: The top 90 African marathoners from 2001 to 2015 were compared with the top 90 non-African marathoners from the same time period across various markers related to specialization age, performance, and career length. Independent t tests were used to identify significant differences (P < .05) between the African and non-African groups. Linear regression was used to explore the relationship between first half-marathon and best full-marathon performance. A 1-way ANOVA and Bonferroni correction was used to assess differences in specialization age and rates of performance improvement and decline. RESULTS: African marathoners were found to specialize, reach peak levels of performance, and retire at younger ages than non-African marathoners (P < .001). In addition, African marathoners were found to be faster at these same career time points and in half-marathon performance (P < .001). There was no significant difference in the number of career marathons run between groups, but African marathoners were found to race more frequently than non-African marathoners (P < .001). Half-marathon performance was positively correlated with marathon performance (r2 = .67). Marathon athletes who specialized at early ages experienced significantly higher rates of improvement than those who specialized at older ages. (P < .05). CONCLUSIONS: The findings suggest that elite African marathoners achieve a greater level of performance at younger ages than their non-African counterparts. Furthermore, current marathon talent-identification practice may benefit from using half-marathon performance.

Incidence of Vacuum Phenomenon Related Intra-articular or Subfascial Gas Found on Computer-Assisted Tomography (CT) Scans of Closed Lower Extremity Fractures.

OBJECTIVES: To determine the incidence of vacuum phenomenon related intra-articular or subfascial gas found on computer-assisted tomography (CT) scans of closed lower extremity fractures. DESIGN: Retrospective Review. SETTING: Level I Trauma Center. PATIENTS/PARTICIPANTS: A total of 153 patients with closed lower extremity fractures. INTERVENTION: CT scans of identified individuals were reviewed for the presence or absence of gaseous accumulations. MAIN OUTCOME MEASUREMENTS: The presence or absence of gas on CT. RESULTS: Twenty seven (17.6%) of the 153 fractures were found to have intra-articular or subfascial gas on CT despite clear documentation, indicating a closed injury with no significant skin compromise. Of the intra-articular fractures (OTA/AO 33B/C, 41B/C and 43B/C), 20% (23 of 113) were found to have gas on CT. All cases were associated with fracture of the tibia (P = 0.002). CONCLUSIONS: Computed tomography demonstrated the presence of intra-articular or subfascial gas in 17.6% (27/153) of closed lower extremity fractures and in 20% (23/113) of closed intra-articular fractures. The possibility of vacuum phenomenon must be considered when using this imaging modality as the confirmatory test for open intra-articular fracture or traumatic arthrotomy. LEVEL OF EVIDENCE: Level IV.