Autophagy is a cellular degradation-recycling system for aggregated proteins and damaged organelles. Although dysregulated autophagy is implicated in various diseases including neurodegeneration, its role in pancreatic beta cells and glucose homeostasis has not been described. We produced mice with beta cell-specific deletion of Atg7 (autophagy-related 7). Atg7 mutant mice showed impaired glucose tolerance and decreased serum insulin level. beta cell mass and pancreatic insulin content were reduced because of increased apoptosis and decreased proliferation of beta cells. Physiological studies showed reduced basal and glucose-stimulated insulin secretion and impaired glucose-induced cytosolic Ca2+ transients in autophagy-deficient beta cells. Morphologic analysis revealed accumulation of ubiquitinated protein aggregates colocalized with p62, which was accompanied by mitochondrial swelling, endoplasmic reticulum distension, and vacuolar changes in beta cells. These results suggest that autophagy is necessary to maintain structure, mass and function of pancreatic beta cells, and its impairment causes insulin deficiency and hyperglycemia because of abnormal turnover and function of cellular organelles.

Epithelial cyst and tubule formation are critical processes that involve transient, highly choreographed changes in cell polarity. Factors controlling these changes in polarity are largely unknown. One candidate factor is the highly conserved eight-member protein complex called the exocyst. We show that during tubulogenesis in an in vitro model system the exocyst relocalized along growing tubules consistent with changes in cell polarity. In yeast, the exocyst subunit Sec10p is a crucial component linking polarized exocytic vesicles with the rest of the exocyst complex and, ultimately, the plasma membrane. When the exocyst subunit human Sec10 was exogenously expressed in epithelial Madin-Darby canine kidney cells, there was a selective increase in the synthesis and delivery of apical and basolateral secretory proteins and a basolateral plasma membrane protein, but not an apical plasma membrane protein. Overexpression of human Sec10 resulted in more efficient and rapid cyst formation and increased tubule formation upon stimulation with hepatocyte growth factor. We conclude that the exocyst plays a central role in the development of epithelial cysts and tubules.

Here we report a microfluidics method to enrich physically deformable cells by mechanical manipulation through artificial microbarriers. Driven by hydrodynamic forces, flexible cells or cells with high metastatic propensity change shape to pass through the microbarriers and exit the separation device, whereas stiff cells remain trapped. We demonstrate the separation of (i) a mixture of two breast cancer cell types (MDA-MB-436 and MCF-7) with distinct deformabilities and metastatic potentials, and (ii) a heterogeneous breast cancer cell line (SUM149), into enriched flexible and stiff subpopulations. We show that the flexible phenotype is associated with overexpression of multiple genes involved in cancer cell motility and metastasis, and greater mammosphere formation efficiency. Our observations support the relationship between tumor-initiating capacity and cell deformability, and demonstrate that tumor-initiating cells are less differentiated in terms of cell biomechanics.cell mechanics | cytoskeleton | genomic profiling C ell deformability is commonly measured using magnetic twisting cytometry, particle tracking rheometry, optical tweezers, micropipette aspiration, atomic force microscope, and other derivative cell stretching or poking methods (1-4). Applications of these methods to stem cells have revealed the greater deformability of the cytoskeleton and nucleoskeleton in less differentiated cells, whereby deformability generally decreases during differentiation to mature cells (5-8). Research on cancer cell deformability has also consistently revealed that increased deformability is correlated with increased metastatic potential (9-15).Despite the success achieved using cell deformability measurements, isolation of cells with differential deformabilities remains a great challenge (10, 16). Microfabrication-assisted technology, using microscale arrays of round or rectangular posts, channels, or other simple patterns, has the potential to solve this problem (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). Here, we focused on the mechanical properties of cancer cells in designing a unique cell purification system for the purpose of generating subpopulations enriched in highly deformable cells. We used microfabrication technology and obtained a subpopulation of SUM149 breast cancer cells with stem-cell-like deformability and mammosphere formation capability.The separation device, a mechanical separation chip (MS-chip), employs artificial microbarriers in combination with hydrodynamic force to separate deformable from stiff cells (Fig. 1A). Both the microbarrier structures and the fluidic parameters are essential to the cell-enrichment process. The most notable feature of the device is the precise placement of the microbarriers to impede the passage of stiff cells. Published in vivo observations suggest that the minimum crossable barrier for cancer cells is ∼8 μm or less (28,29). Here, we took those barrier dimensions into account in designing the MSchip to separate cells based on perfusion through constrictions. As...

The remarkable adaptive and regenerative capacity of skeletal muscle is regulated by several transcription factors and pathways. Here we show that the transcription factor Prox1 is an important regulator of myoblast differentiation and of slow muscle fibre type. In both rodent and human skeletal muscles Prox1 is specifically expressed in slow muscle fibres and in muscle stem cells called satellite cells. Prox1 activates the NFAT signalling pathway and is necessary and sufficient for the maintenance of the gene program of slow muscle fibre type. Using lineage-tracing we show that Prox1-positive satellite cells differentiate into muscle fibres. Furthermore, we provide evidence that Prox1 is a critical transcription factor for the differentiation of myoblasts via bi-directional crosstalk with Notch1. These results identify Prox1 as an essential transcription factor that regulates skeletal muscle phenotype and myoblast differentiation by interacting with the NFAT and Notch pathways.