The de novo formation of secretory lumens plays an important role during organogenesis. It involves the establishment of a cellular apical pole and the elongation of luminal cavities. The molecular parameters controlling cell polarization have been heavily scrutinized. In particular, signalling from the extracellular matrix (ECM) proved essential to the proper localization of the apical pole by directed protein transport. However, little is known about the regulation of the shape and the directional development of lumen into tubes. We demonstrate that the spatial scaffolding of cells by ECM can control tube shapes and can direct their elongation. We developed a minimal organ approach comprising of hepatocyte doublets cultured in artificial microniches to precisely control the spatial organization of cellular adhesions in three dimensions. This approach revealed a mechanism by which the spatial repartition of integrin-based adhesion can elicit an anisotropic intercellular mechanical stress guiding the osmotically driven elongation of lumens in the direction of minimal tension. This mechanical guidance accounts for the different morphologies of lumen in various microenvironmental conditions.

Fetal hypoxia is a common risk factor that has been associated with a range of CNS disorders including epilepsy, schizophrenia, and autism. Cellular and molecular mechanisms through which hypoxia may damage the developing brain are incompletely understood but are likely to involve disruption of the laminar organization of the cerebral cortex. Lysophosphatidic acid (LPA) is a bioactive lipid capable of cortical influences via one or more of six cognate G protein-coupled receptors, LPA 1-6 , several of which are enriched in fetal neural progenitor cells (NPCs). Here we report that fetal hypoxia induces cortical disruption via increased LPA 1 signaling involving stereotyped effects on NPCs: N-cadherin disruption, displacement of mitotic NPCs, and impaired neuronal migration, as assessed both ex vivo and in vivo. Importantly, genetic removal or pharmacological inhibition of LPA 1 prevented the occurrence of these hypoxia-induced phenomena. Hypoxia resulted in overactivation of LPA 1 through selective inhibition of G protein-coupled receptor kinase 2 expression and activation of downstream pathways including G αi and Ras-related C3 botulinum toxin substrate 1. These data identify stereotyped and selective hypoxia-induced cerebral cortical disruption requiring LPA 1 signaling, inhibition of which can reduce or prevent disease-associated sequelae, and may take us closer to therapeutic treatment of fetal hypoxia-induced CNS disorders and possibly other forms of hypoxic injury.uring fetal development, the embryonic brain is susceptible to hypoxic insults (1) that can contribute to a range of neurological and psychiatric abnormalities including autism, schizophrenia, and epilepsy (2-4). These diseases or disorders are associated with cerebral cortical abnormalities in neuronal migration (5-7), which are thought to occur during the neurogenic period to produce disruption (cortical dysplasia) in the laminar organization of the cortex. Despite the identification of fetal hypoxia as a significant risk factor for these and other afflictions of the brain, mechanistic information is lacking on how hypoxia might contribute to these pathologies.

The liver is unique in its capacity to regenerate after injury, during which hepatocytes actively divide and establish cell-cell contacts through cell adhesion complexes. Here, we demonstrate that the loss of α-catenin, a well-established adhesion component, dramatically disrupts liver regeneration. Using a partial hepatectomy model, we show that regenerated livers from α-catenin knockdown mice are grossly larger than control regenerated livers, with an increase in cell size and proliferation. This increased proliferation correlated with increased YAP activation, implicating α-catenin in the Hippo/YAP pathway. Additionally, α-catenin knockdown mice exhibited a phenotype reminiscent of clinical cholestasis, with drastically altered bile canaliculi, elevated levels of bile components and signs of jaundice and inflammation. The disrupted regenerative capacity is a result of actin cytoskeletal disorganisation, leading to a loss of apical microvilli, dilated lumens in the bile canaliculi, and leaky tight junctions. This study illuminates a novel, essential role for α-catenin in liver regeneration.