The intensities of canonical senescence biomarkers integrate the duration of cell-cycle withdrawal.

Senescence, a state of irreversible cell-cycle withdrawal, is difficult to distinguish from quiescence, a state of reversible cell-cycle withdrawal. This difficulty arises because quiescent and senescent cells are defined by overlapping biomarkers, raising the question of whether these states are truly distinct. To address this, we use single-cell time-lapse imaging to distinguish slow-cycling cells that spend long periods in quiescence from cells that never cycle after recovery from senescence-inducing treatments, followed by staining for various senescence biomarkers. We find that the staining intensity of multiple senescence biomarkers is graded rather than binary and reflects the duration of cell-cycle withdrawal, rather than senescence per se. Together, our data show that quiescent and apparent senescent cells are nearly molecularly indistinguishable from each other at a snapshot in time. This suggests that cell-cycle withdrawal itself is graded rather than binary, where the intensities of senescence biomarkers integrate the duration of past cell-cycle withdrawal.

The intensities of canonical senescence biomarkers integrate the duration of cell-cycle withdrawal.

Senescence, a state of permanent cell-cycle withdrawal, is difficult to distinguish from quiescence, a transient state of cell-cycle withdrawal. This difficulty arises because quiescent and senescent cells are defined by overlapping biomarkers, raising the question of whether quiescence and senescence are truly distinct states. To address this, we used single-cell time-lapse imaging to distinguish slow-cycling quiescent cells from bona fide senescent cells after chemotherapy treatment, followed immediately by staining for various senescence biomarkers. We found that the staining intensity of multiple senescence biomarkers is graded rather than binary and primarily reflects the duration of cell-cycle withdrawal, rather than senescence per se. Together, our data suggest that quiescence and senescence are not distinct cellular states but rather fall on a continuum of cell-cycle withdrawal, where the intensities of canonical senescence biomarkers reflect the likelihood of cell-cycle re-entry.

Impact of polygenic risk communication: an observational mobile application-based coronary artery disease study.

We developed a smartphone application, MyGeneRank, to conduct a prospective observational cohort study (NCT03277365) involving the automated generation, communication, and electronic capture of response to a polygenic risk score (PRS) for coronary artery disease (CAD). Adults with a smartphone and an existing 23andMe genetic profiling self-referred to the study. We evaluated self-reported actions taken in response to personal CAD PRS information, with special interest in the initiation of lipid-lowering therapy. 19% (721/3,800) of participants provided complete responses for baseline and follow-up use of lipid-lowering therapy. 20% (n = 19/95) of high CAD PRS vs 7.9% (n = 8/101) of low CAD PRS participants initiated lipid-lowering therapy at follow-up (p-value = 0.002). Both the initiation of statin and non-statin lipid-lowering therapy was associated with degree of CAD PRS: 15.2% (n = 14/92) vs 6.0% (n = 6/100) for statins (p-value = 0.018) and 6.8% (n = 8/118) vs 1.6% (n = 2/123) for non-statins (p-value = 0.022) in high vs low CAD PRS, respectively. High CAD PRS was also associated with earlier initiation of lipid lowering therapy (average age of 52 vs 65 years in high vs low CAD PRS respectively, p-value = 0.007). Overall, degree of CAD PRS was associated with use of any lipid-lowering therapy at follow-up: 42.4% (n = 56/132) vs 28.5% (n = 37/130) (p-value = 0.009). We find that digital communication of personal CAD PRS information is associated with increased and earlier lipid-lowering initiation in individuals of high CAD PRS. Loss to follow-up is the primary limitation of this study. Alternative communication routes, and long-term studies with EHR-based outcomes are needed to understand the generalizability and durability of this finding.

CRISPR-Cas-Mediated Tethering Recruits the Yeast HMR Mating-Type Locus to the Nuclear Periphery but Fails to Silence Gene Expression.

To investigate the relationship between genome structure and function, we have developed a programmable CRISPR-Cas system for nuclear peripheral recruitment in yeast. We benchmarked this system at the HMR and GAL2 loci, both of which are well-characterized model systems for localization to the nuclear periphery. Using microscopy and gene silencing assays, we demonstrate that CRISPR-Cas-mediated tethering can recruit the HMR locus but does not detectably silence reporter gene expression. A previously reported Gal4-mediated tethering system does silence gene expression, and we demonstrate that the silencing effect has an unexpected dependence on the properties of the protein tether. The CRISPR-Cas system was unable to recruit GAL2 to the nuclear periphery. Our results reveal potential challenges for synthetic genome structure perturbations and suggest that distinct functional effects can arise from subtle structural differences in how genes are recruited to the periphery.

CRISPR-Cas-Mediated Chemical Control of Transcriptional Dynamics in Yeast.

Synthetic CRISPR-Cas transcription factors enable the construction of complex gene-expression programs, and chemically inducible systems allow precise control over the expression dynamics. To provide additional modes of regulatory control, we have constructed a chemically inducible CRISPR activation (CRISPRa) system in yeast that is mediated by recruitment to MS2-functionalized guide RNAs. We use reporter gene assays to systematically map the dose dependence, time dependence, and reversibility of the system. Because the recruitment function is encoded at the level of the guide RNA, it is straightforward to target multiple genes and independently regulate expression dynamics at individual targets. This approach provides a new method to engineer sophisticated, multigene programs with precise control over the dynamics of gene expression.