Biology subjects

Ben Zvi, A.

Publications and source records attributed to Ben Zvi, A..

3 recordsLinked to original sources

bioRxiv2026

Lef1 is dispensable for blood-brain barrier integrity despite its dominant role in endothelial Wnt signaling

The blood-brain barrier (BBB) is a specialized vascular structure essential for CNS homeostasis, whose formation and maintenance are governed by the canonical Wnt signaling pathway. While the upstream ligands and receptors are well-characterized, the downstream transcriptional architecture remains poorly understood. Here, we investigate the functional requirement for Lef1, the most abundant Tcf/Lef transcription factor and a hallmark readout of Wnt activity in brain endothelial cells (BECs). Utilizing a conditional, endothelial-specific deletion strategy in mice, we demonstrate that loss of Lef1 during either embryonic development or adult homeostasis significantly dampens Wnt transcriptional output. Surprisingly, high-resolution molecular and functional analysis reveals that this reduction results in only minor dysregulation of the BBB-specific gene program and is insufficient to trigger barrier breakdown. Our results establish that Lef1 is not an obligatory effector of the Wnt-dependent BBB maintenance program. These findings suggest a resilient transcriptional framework where redundant Tcf/Lef family members or alternative regulatory circuits preserve CNS microvasculature function, providing new insights into the genetic robustness of the blood-brain barrier. Research HighlightsO_LILef1 is the predominant Tcf/Lef transcription factor in the brain endothelium and a hallmark of vascular Wnt signaling. C_LIO_LIEndothelial-specific Lef1 deletion significantly attenuates Wnt transcriptional output during both CNS vascular development and adult homeostasis. C_LIO_LILoss of Lef1 causes only minor perturbations in the BBB-specific gene program, rather than a global loss of endothelial identity. C_LIO_LIStructural and functional BBB integrity is preserved in the absence of Lef1, revealing a high degree of vascular resilience. C_LIO_LIThe findings demonstrate that Lef1 is not an obligatory effector for the maintenance of the specialized CNS microvasculature. C_LI

neuroscience↗

bioRxiv2024

Diverse patterns of intra-host genetic diversity in chronically infected SARS-CoV-2 patients

In rare individuals with a severely immunocompromised system, chronic infections of SARS-CoV-2 may develop, where the virus replicates in the body for months. Sequencing of some chronic infections has uncovered dramatic adaptive evolution and fixation of mutations reminiscent of lineage-defining mutations of variants of concern (VOCs). This has led to the prevailing hypothesis that VOCs emerged from chronic infections. To examine the mutation dynamics and intra-host genomic diversity of SARS-CoV-2 during chronic infections, we focused on a cohort of nine immunocompromised individuals with chronic infections and performed longitudinal sequencing of viral genomes. We show that sequencing errors may cause erroneous inference of high genetic diversity, and to overcome this we used duplicate sequencing across patients and time-points, allowing us to distinguish errors from low frequency mutations. We further find recurrent low frequency mutations that we flag as most likely sequencing errors. This stringent approach allowed us to reliably infer low frequency mutations and their dynamics across time. We inferred a synonymous divergence rate of the virus of [~]2x10-6 mutations/base/day, consistent with the SARS-CoV-2 mutation rate estimated in tissue culture. The rate of non-synonymous divergence varied widely among the different patients. We highlight two patients with opposing patterns: in one patient the rate of divergence was zero, yet this patient harbored multiple presumably defective viruses at low frequencies throughout the infection. Another patient exhibited dramatic adaptive evolution, including clonal competition. Overall, our results suggest that the emergence of highly divergent variants from chronic infections is likely a very rare event and this emphasizes the need to better understand the conditions that allow such emergence events.

evolutionary biology↗

bioRxiv2024

Navigating a fine balance: point-mutant cheater viruses disrupt the viral replication cycle

Cheater viruses, alternatively denoted as defective interfering viruses, cannot replicate on their own yet replicate faster than the wild type (WT) when the two viruses coinfect the same cell. Cheaters must possess dual genetic features: a defect, which leads to their inability to infect cells on their own, and a selective advantage over WT during co-infection. Previously, we have discovered two point-mutant cheaters of the MS2 bacteriophage. Here, we set out to discover the possible repertoire of cheater MS2 viruses by performing experimental evolution at a very high multiplicity of infection (MOI). Our results revealed a third point-mutant cheater that arose in eight biological replicas. Each of the three cheaters disrupts the fine balance necessary for phage replication, in different ways that create a defect + advantage. We found that over time, the point mutant cheaters accumulate additional "helper" mutations, which alter other stages of the viral replication cycle, complementing the disruptions created by the original cheater. Intriguingly, cheater and helper mutations almost always reside in very close proximity on the genome. This region encodes for multiple functions: overlapping reading frames as well as overlapping RNA structures critical for transitioning from one stage to another in the viral replication cycle. This region of overlap explains the dual functions of cheaters, as one mutation can have pleiotropic effects. Overall, these findings underscore how viruses, whose dense genomes often have overlapping functions, can easily evolve point-mutant cheaters, and how cheaters can evolve to alter the intricate balance of the viral replication cycle.

evolutionary biology↗