Analysis of Pre-clerkship Medical Students' Perceptions and Performance During the COVID-19 Pandemic.

Purpose: Virtual instruction became the primary educational delivery method for pre-clerkship medical students during the COVID-19 pandemic. The aims of this study were to evaluate the effectiveness of a virtual and blended pre-clerkship curriculum and to assess its impact on students. Methods: We surveyed 223 1st- and 2nd-year medical students (MS1s and MS2s) enrolled at the Paul L Foster School of Medicine. We analyzed student satisfaction with their courses, along with summative exam scores, compared to previous academic years. Results: The survey was completed by 125 of 223 students (56%). Most students changed their study methods (78%), experienced technical issues (85%), and had difficulty communicating with faculty (62%). MS1s were significantly more likely than MS2s to report difficulty in adjusting to virtual instruction (p = 0.037) and a negative impact on their learning skills (p = 0.005) and academic performance (p = 0.003). Students reported the virtual environment negatively affected their social skills (77%), connectedness to peers (89%), and professional development (62%). MS1s were more likely than MS2s to perceive a negative effect on their sense of wellness (p = 0.002). The overall satisfaction with the courses was similar to previous academic years. Student performance in the summative examination of the first virtually delivered unit was lower (p = 0.007) than the previous year's cohorts. Conclusion: The difference in MS1s and MS2s perceptions of virtual and blended instruction highlights the importance of face-to-face learning during the first year. Benefits and drawbacks were identified which may help inform educators when designing future learning models. Supplementary Information: The online version contains supplementary material available at 10.1007/s40670-022-01723-6.

Cdc6 is required for meiotic spindle assembly in Xenopus oocytes.

During the maturation of Xenopus oocytes, Cdc6 expression is necessary to establish replication competence to support early embryonic DNA replication. However, Cdc6 is expressed before the completion of MI, at a time when its function as a replication factor is not required, suggesting additional roles for Cdc6 in meiosis. Confocal immunofluorescence microscopy revealed that Cdc6 protein was distributed around the spindle precursor at the time of germinal vesicle breakdown (GVBD), and localized to the margin of the nascent spindle early in prometaphase. Cdc6 subsequently localized to spindle poles in late prometaphase, where it remained until metaphase arrest. Microinjection of antisense oligonucleotides specific for Cdc6 mRNA disrupted spindle assembly, resulting in defects including delayed spindle assembly, misoriented and unattached anaphase spindles, monasters, multiple spindles, microtubule aggregates associated with condensed chromosomes, or the absence of recognizable spindle-like structures, depending on the level of residual Cdc6 expression. Furthermore, Cdc6 co-localized with γ-tubulin in centrosomes during interphase in all somatic cells analyzed, and associated with spindle poles in mitotic COS cells. Our data suggest a role for Cdc6 in spindle formation in addition to its role as a DNA replication factor.

Geminin stabilizes Cdt1 during meiosis in Xenopus oocytes.

During the mitotic cell cycle, Geminin can act both as a promoter and inhibitor of initiation of DNA replication. As a promoter, Geminin stabilizes Cdt1 and facilitates its accumulation leading to the assembly of the pre-replication complex on DNA. As an inhibitor, Geminin prevents Cdt1 from loading the mini-chromosome maintenance complex onto pre-replication complexes in late S, G(2), and M phases. Here we show that during meiosis Geminin functions as a stabilizer of Cdt1 promoting its accumulation for the early division cycles of the embryo. Depletion of Geminin in Xenopus immature oocytes leads to a decrease of Cdt1 protein levels during maturation and after activation of these oocytes. Injection of exogenous recombinant Geminin into the depleted oocytes rescues Cdt1 levels demonstrating that Geminin stabilizes Cdt1 during meiosis and after fertilization. Furthermore, Geminin-depleted oocytes did not replicate their DNA after meiosis I indicating that Geminin does not act as an inhibitor of initiation of DNA replication between meiosis I and meiosis II.

Xenopus CDC7/DRF1 complex is required for the initiation of DNA replication.

The Cdc7 kinase is essential for the initiation of DNA replication in eukaryotes. Two regulatory subunits of the Xenopus Cdc7 kinase have been identified: XDbf4 and XDrf1. In this study we determined the expression pattern of XDbf4 and XDrf1 and examined their involvement in DNA replication. We show that XDrf1 expression is restricted to oogenesis and early embryos, whereas XDbf4 is expressed throughout development. Immunodepletion from Xenopus egg extracts indicated that both proteins are only found in complexes with XCdc7 and there is a 5-fold molar excess of the XCdc7/Drf1 over SCdc7/Dbf4 complexes. Both complexes exhibit kinase activity and are differentially phosphorylated during the cell cycle. Depletion of the XCdc7/Drf1 from egg extracts inhibited DNA replication, whereas depletion of XCdc7/Dbf4 had little effect. Chromatin binding studies indicated that XCdc7/Drf1 is required for pre-replication complex activation but not their assembly. XCdc7/Dbf4 complexes bound to the chromatin in two steps: the first step was independent of pre-replication complex assembly and the second step was dependent on pre-replication complex activation. By contrast, binding of XCdc7/Drf1 complexes was entirely dependent on pre-replication complex assembly. Finally, we present evidence that the association of the two complexes on the chromatin is not regulated by ATR checkpoint pathways that result from DNA replication blocks. These data suggest that Cdc7/Drf1 but not Cdc7/Dbf4 complexes support the initiation of DNA replication in Xenopus egg extracts and during early embryonic development.

Cdc6 synthesis regulates replication competence in Xenopus oocytes.

The early division cycles of an embryo rely on the oocyte's ability to replicate DNA. During meiosis, oocytes temporarily lose this ability. After a single round of pre-meiotic S-phase, oocytes enter meiosis and rapidly arrest at prophase of meiosis I (G2). Upon hormonal stimulation, arrested oocytes resume meiosis, re-establish DNA replication competence in meiosis I shortly after germinal vesicle breakdown (GVBD), but repress replication until fertilization. How oocytes lose and regain replication competence during meiosis are important questions underlying the production of functional gametes. Here we show that the inability of immature Xenopus oocytes to replicate is linked to the absence of the Cdc6 protein and the cytoplasmic localization of other initiation proteins. Injection of Cdc6 protein into immature oocytes does not induce DNA replication. However, injection of Cdc6 into oocytes undergoing GVBD is sufficient to induce DNA replication in the absence of protein synthesis. Our results show that GVBD and Cdc6 synthesis are the only events that limit the establishment of the oocyte's replication competence during meiosis.