Flaminia Kaluthantrige Don

Cryo-focused ion beam milling has substantially advanced our understanding of molecular processes by opening windows into cells. However, applying this technique to complex samples, such as tissues, has presented considerable technical challenges. Here we introduce an innovative adaptation of the cryo-lift-out technique, serialized on-grid lift-in sectioning for tomography (SOLIST), addressing these limitations. SOLIST enhances throughput, minimizes ice contamination and improves sample stability for cryo-electron tomography. It thereby facilitates the high-resolution imaging of a wide range of specimens. We illustrate these advantages on reconstituted liquid–liquid phase-separated droplets, brain organoids and native tissues from the mouse brain, liver and heart. With SOLIST, cellular processes can now be investigated at molecular resolution directly in native tissue. Furthermore, our method has a throughput high enough to render cryo-lift-out a competitive tool for structural biology. This opens new avenues for unprecedented insights into cellular function and structure in health and disease, a ‘biopsy at the nanoscale’. Serialized on-grid lift-in sectioning for tomography (SOLIST) improves the throughput of the serial lift-out technique for creating lamellas, addressing a major bottleneck in the use of cryo-electron tomography for in situ structural biology.

The acquisition of higher intellectual abilities that distinguish humans from their closest relatives correlates greatly with the expansion of the cerebral cortex. This expansion is a consequence of an increase in neuronal cell production driven by the higher proliferative capacity of neural progenitor cells, in particular basal radial glia (bRG). Furthermore, when the proliferation of neural progenitor cells is impaired and the final neuronal output is altered, severe neurodevelopmental disorders can arise. To effectively study the cell biology of human bRG, genetically accessible human experimental models are needed. With the pioneering success to isolate and culture pluripotent stem cells in vitro , we can now routinely investigate the developing human cerebral cortex in a dish using three-dimensional multicellular structures called organoids. Here, we will review the molecular and cell biological features of bRG that have recently been elucidated using brain organoids. We will further focus on the application of this simple model system to study in a mechanistically actionable way the molecular and cellular events in bRG that can lead to the onset of various neurodevelopmental diseases.

Abstract Cryo-focused ion beam milling has enabled groundbreaking structural discoveries in native cells. Progress toward medically relevant applications, however, has been slow. We here present an adaptation of the cryo-lift out procedure for Serialized On-grid Lift-In Sectioning for Tomography (SOLIST), which increases throughput, reduces ice contamination, and enhances sample stability. With these improvements, new specimens, ranging from high-pressure frozen reconstituted LLPS droplets to human forebrain organoids, are accessible to cryo-electron tomography.

Human liver ductal epithelium is morphologically, functionally, and transcriptionally heterogeneous. Understanding the impact of this heterogeneity has been challenging due to the absence of systems that recapitulate this heterogeneity in vitro. Here, we found that human liver cholangiocyte organoids do not retain the complex cellular heterogeneity of the native ductal epithelium. Inspired by the knowledge of the cellular niche, we refined our previous organoid medium to fully capture the in vivo cellular heterogeneity. We employed this refined system to analyze the relationships between human biliary epithelial cell states. In our refined model, cholangiocytes transition toward hepatocyte-like states through a bipotent state. Additionally, inhibiting WNT signaling enhances the differentiation capacity of the cells toward hepatocyte-like states. By capturing the in vivo cholangiocyte heterogeneity, our improved organoid model represents a platform to investigate the impact of the different liver ductal cell states in cell plasticity, regeneration, and disease.