Making the connection: ciliary adhesion complexes anchor basal bodies to the actin cytoskeleton

Spatially defined EGF receptor activation reveals an F-actin-dependent phospho-Erk signaling complex

We investigated the association of signaling proteins with epidermal growth factor (EGF) receptors (EGFR) using biotinylated EGF bound to streptavidin that is covalently coupled in an ordered array of micron-sized features on silicon surfaces. Using NIH-3T3 cells stably expressing EGFR, we observe concentration of fluorescently labeled receptors and stimulated tyrosine phosphorylation that are spatially confined to the regions of immobilized EGF and quantified by cross-correlation analysis. We observe recruitment of phosphorylated paxillin to activated EGFR at these patterned features, as well as β1-containing integrins that preferentially localize to more peripheral EGF features, as quantified by radial fluorescence analysis. In addition, we detect recruitment of EGFP-Ras, MEK, and phosphorylated Erk to patterned EGF in a process that depends on F-actin and phosphoinositides. These studies reveal and quantify the coformation of multiprotein EGFR signaling complexes at the plasma membrane in response to micropatterned growth factors.

Ciliary inclusion disease: report of a new primary ciliary dyskinesia variant

Biopsies from 6 children with clinical presentations suggestive of primary ciliary dyskinesia (PCD) displayed respiratory epithelial cells with disorganized accumulations of basal bodies within the cytoplasm and large intracytoplasmic vesicles into which projected numerous microvilli and cilia. Microvilli, but few cilia, were present at the cell surface. Ultrastructural study revealed a variety of nonspecific abnormalities but demonstrated the cilia generally to be morphologically normal, suggesting that the cause of cilia malfunction was not any recognized primary cause or secondary effect. Repeat studies from 2 patients produced similar findings. It is proposed that this entity, termed ciliary inclusion disease, represents a variant form of PCD manifesting as a consequence of improper ciliogenesis caused by inhibited cytoskeleton-regulated migration of basal bodies to the luminal surface of the airway respiratory epithelial cells.

FAK transduces extracellular forces that orient the mitotic spindle and control tissue morphogenesis

Spindle orientation is critical for proper morphogenesis of organs and tissues as well as for the maintenance of tissue morphology. Although significant progress has been made in understanding the mechanisms linking the cell cortex to the spindle and the well-documented role that extracellular forces play in spindle orientation, how such forces are transduced to the cortex remains poorly understood. Here we report that focal adhesion kinase (FAK) is necessary for correct spindle orientation and as a result, indispensable for proper epithelial morphogenesis in the vertebrate embryo. We show that FAK's role in spindle orientation is dependent on its ability to localize at focal adhesions and its interaction with paxillin, but is kinase activity independent. Finally, we present evidence that FAK is required for external force-induced spindle reorientation, suggesting that FAK's involvement in this process stems from a role in the transduction of external forces to the cell cortex.

Multiciliated cells

Cilia are microtubule-based projections that serve a wide variety of essential functions in animal cells. Defects in cilia structure or function have recently been found to underlie diverse human diseases. While many eukaryotic cells possess only one or two cilia, some cells, including those of many unicellular organisms, exhibit many cilia. In vertebrates, multiciliated cells are a specialized population of post-mitotic cells decorated with dozens of motile cilia that beat in a polarized and synchronized fashion to drive directed fluid flow across an epithelium. Dysfunction of human multiciliated cells is associated with diseases of the brain, airway and reproductive tracts. Despite their importance, multiciliated cells are relatively poorly studied and we are only beginning to understand the mechanisms underlying their development and function. Here, we review the general phylogeny and physiology of multiciliation and detail our current understanding of the developmental and cellular events underlying the specification, differentiation and function of multiciliated cells in vertebrates.

Primary cilium-associated genes mediate bone marrow stromal cell response to hypoxia

Currently there is intense interest in using mesenchymal stem cells (MSC) for therapeutic interventions in many diseases and conditions. To accelerate the therapeutic use of stem cells we must understand how they sense their environment. Primary cilia are an extracellular sensory organelle present on most growth arrested cells that transduce information about the cellular environment into cells, triggering signaling cascades that have profound effects on development, cell cycle, proliferation, differentiation and migration. Migrating cells likely encounter differing oxygen tensions, therefore we investigated the effect of oxygen tension on cilia. Using bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) we found that oxygen tension significantly affected the length of cilia in primary BMSCs. Chronic exposure to hypoxia specifically down-regulated genes involved in hedgehog signaling and re-localized the Smo and Gli2 proteins to cilia. Investigating the effects of chemotactic migration on cilia, we observed significantly longer cilia in migrating cells which was again, strongly influenced by oxygen tension. Finally, using computational modeling we identified links between migration and ciliation signaling pathways, characterizing the novel role of HSP90 and PI3K signaling in regulating BMSC cilia length. These findings enhance our current understanding of BMSC adaptions to hypoxia and advance our knowledge of BMSC biology and cilia regulation.