There exists a conspicuous gap of knowledge about the organization of life at mesoscopic levels. Ultra-fast coherent diffractive imaging with X-ray free-electron lasers can probe structures at the relevant length scales and may reach sub-nanometer resolution on micron-sized living cells. Here we show that we can introduce a beam of aerosolised cyanobacteria into the focus of the Linac Coherent Light Source and record diffraction patterns from individual living cells at very low noise levels and at high hit ratios. We obtain twodimensional projection images directly from the diffraction patterns, and present the results as synthetic X-ray Nomarski images calculated from the complex-valued reconstructions. We further demonstrate that it is possible to record diffraction data to nanometer resolution on live cells with X-ray lasers. Extension to sub-nanometer resolution is within reach, although improvements in pulse parameters and X-ray area detectors will be necessary to unlock this potential.

Cdc42a member of the small Rho GTPase familyregulates cell polarity across organisms from yeast to humans. It is an essential regulator of polarized morphogenesis in epithelial cells, through coordination of apical membrane morphogenesis, lumen formation and junction maturation. In parallel, work in yeast and Caenorhabditis elegans has provided important clues as to how this molecular switch can generate and regulate polarity through localized activation or inhibition, and cytoskeleton regulation. Recent studies have revealed how important and complex these regulations can be during epithelial morphogenesis. This complexity is mirrored by the fact that Cdc42 can exert its function through many effector proteins. In epithelial cells, these include atypical PKC (aPKC, also known as PKC-3), the P21activated kinase (PAK) family, myotonic dystrophy-related Cdc42 binding kinase beta (MRCKβ, also known as CDC42BPB) and neural Wiskott-Aldrich syndrome protein (N-WASp, also known as WASL).Here, we review how the spatial regulation of Cdc42 promotes polarity and polarized morphogenesis of the plasma membrane, with a focus on the epithelial cell type.

Profilin is a well-known regulator of actin filament formation. It indirectly associates with microtubules and influences their growth rate. Formins are the linker molecules, and the turnover of the actin microfilament system balances profilin association with the microtubules.

SummaryThe ability of epithelial cells to assemble into sheets relies on their zonula adherens (ZA), a circumferential belt of adherens junction (AJ) material, which can be remodeled during development to shape organs. Here, we show that during ZA remodeling in a model neuroepithelial cell, the Cdc42 effector P21-activated kinase 4 (Pak4/Mbt) regulates AJ morphogenesis and stability through β-catenin (β-cat/Arm) phosphorylation. We find that β-catenin phosphorylation by Mbt, and associated AJ morphogenesis, is needed for the retention of the apical determinant Par3/Bazooka at the remodeling ZA. Importantly, this retention mechanism functions together with Par1-dependent lateral exclusion of Par3/Bazooka to regulate apical membrane differentiation. Our results reveal an important functional link between Pak4, AJ material morphogenesis, and polarity remodeling during organogenesis downstream of Par3.

Cdc42 regulates epithelial morphogenesis together with the Par complex (Baz/Par3-Par6-aPKC), Crumbs (Crb/CRB3) and Stardust (Sdt/PALS1). However, how these proteins work together and interact during epithelial morphogenesis is not well understood. To address this issue, we used the genetically amenable Drosophila pupal photoreceptor and follicular epithelium. We show that during epithelial morphogenesis active Cdc42 accumulates at the developing apical membrane and cell-cell contacts, independently of the Par complex and Crb. However, membrane localization of Baz, Par6-aPKC and Crb all depend on Cdc42. We find that although binding of Cdc42 to Par6 is not essential for the recruitment of Par6 and aPKC to the membrane, it is required for their apical localization and accumulation, which we find also depends on Par6 retention by Crb. In the pupal photoreceptor, membrane recruitment of Par6-aPKC also depends on Baz. Our work shows that Cdc42 is required for this recruitment and suggests that this factor promotes the handover of Par6-aPKC from Baz onto Crb. Altogether, we propose that Cdc42 drives morphogenesis by conferring apical identity, Par-complex assembly and apical accumulation of Crb.

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Prioritizing treatments for individual cancer patients remains challenging, and performing co-clinical studies using patient-derived models in real-time is often unfeasible. To circumvent these challenges, we introduce OncoLoop, a precision medicine framework that predicts drug sensitivity in human tumors and their pre-existing high-fidelity (cognate) model(s) by leveraging drug perturbation profiles. As proof-of-concept, we applied OncoLoop to prostate cancer (PCa) using genetically-engineered mouse models (GEMMs) that recapitulate a broad spectrum of disease states, including castration-resistant, metastatic, and neuroendocrine prostate cancer. Interrogation of human PCa cohorts by Master Regulator (MR) conservation analysis revealed that most advanced PCa patients were represented by at least one cognate GEMM-derived tumor (GEMM-DT). Drugs predicted to invert MR activity in patients and their cognate GEMM-DTs were successfully validated in allograft, syngeneic, and patient-derived xenograft (PDX) models of tumors and metastasis. Furthermore, Oncoloop-predicted drugs enhanced the efficacy of clinically-relevant drugs, namely the PD1 inhibitor, nivolumab, and the AR-inhibitor, enzalutamide.

Prioritizing cancer treatment at the individual patient level remains challenging and performing co-clinical studies using patient-derived models in real-time is often unfeasible. To circumvent these challenges, we introduce OncoLoop, a precision medicine framework to predict drug sensitivity in both a human tumor and its highest-fidelity (cognate) model(s), for contextual in vivo validation, by leveraging perturbational profiles of clinically-relevant oncology drugs. As proof-of-concept, we applied OncoLoop to prostate cancer using a series of genetically engineered mouse models (GEMMs) that capture the broad spectrum of disease states, including metastatic, castration-resistant, and neuroendocrine prostate cancer. Interrogation of published cohorts revealed that most patients were represented by at least one cognate GEMM-derived tumor (GEMM-DT), based on Master Regulator (MR) conservation analysis. Drugs recurrently predicted to invert MR protein activity in patients and their cognate GEMM-DTs were successfully validated, including in two cognate allografts and one patient derived xenograft (PDX). OncoLoop is highly generalizable and can be extended to other cancers and other pathologies.