utilizing-custom-designed-galvanotaxis-chambers-to-study-directional

Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells

The physiological electric field serves specific biological functions, such as directing cell migration in embryo development, neuronal outgrowth and ...

University of California, Davis

In most animals, successful segregation of female meiotic chromosomes involves sequential associations of the meiosis I and meiosis II spindles with the cell cortex so that extra chromosomes can be deposited in polar bodies. The resulting reduction in chromosome number is essential to prevent the generation of polyploid embryos after fertilization. Using time-lapse imaging of living Caenorhabditis elegans oocytes containing fluorescently labeled chromosomes or microtubules, we have characterized the movements of meiotic spindles relative to the cell cortex. Spindle assembly initiated several microns from the cortex. After formation of a bipolar structure, the meiosis I spindle translocated to the cortex. When microtubules were partially depleted, translocation of the bivalent chromosomes to the cortex was blocked without affecting cell cycle timing. In oocytes depleted of the microtubule-severing enzyme, MEI-1, spindles moved to the cortex, but association with the cortex was unstable. Unlike translocation of wild-type spindles, movement of MEI-1-depleted spindles was dependent on FZY-1/CDC20, a regulator of the metaphase/anaphase transition. We observed a microtubule and FZY-1/CDC20-dependent circular cytoplasmic streaming in wild-type and mei-1 mutant embryos during meiosis. We propose that, in mei-1 mutant oocytes, this cytoplasmic streaming is sufficient to drive the spindle into the cortex. Cytoplasmic streaming is not the normal spindle translocation mechanism because translocation occurred in the absence of cytoplasmic streaming in embryos depleted of either the orbit/CLASP homolog, CLS-2, or FZY-1. These results indicate a direct role of microtubule severing in translocation of the meiotic spindle to the cortex.

MEI-1/katanin is required for translocation of the meiosis I spindle to the oocyte cortex in C elegans.

In animals, female meiotic spindles are attached to the egg cortex in a perpendicular orientation at anaphase to allow the selective disposal of three haploid chromosome sets into polar bodies. We have identified a complex of interacting Caenorhabditis elegans proteins that are involved in the earliest step in asymmetric positioning of anastral meiotic spindles, translocation to the cortex. This complex is composed of the kinesin-1 heavy chain orthologue, UNC-116, the kinesin light chain orthologues, KLC-1 and -2, and a novel cargo adaptor, KCA-1. Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex. After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex. This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

Kinesin-1 mediates translocation of the meiotic spindle to the oocyte cortex through KCA-1, a novel cargo adapter.

Keratinocytes represent the major cell type of the uppermost layer of human skin, the epidermis. Using AFM-based single cell compression, the ability of individual keratinocytes to resist external pressure and global rupturing forces is investigated and compared with various cell types. Keratinocytes are found to be 6-70 times stiffer than other cell types, such as white blood, breast epithelial, fibroblast, or neuronal cells, and in contrast to other cell types they retain high mechanic strength even after the cell's death. The absence of membrane rupturing peaks in the force-deformation profiles of keratinocytes and their high stiffness during a second load cycle suggests that their unique mechanical resistance is dictated by the cytoskeleton. A simple analytical model enables the quantification of Young's modulus of keratinocyte cytoskeleton, as high as 120-340 Pa. Selective disruption of the two major cytoskeletal networks, actin filaments and microtubules, does not significantly affect keratinocyte mechanics. F-actin is found to impact cell deformation under pressure. During keratinocyte compression, the plasma membrane stretches to form peripheral blebs. Instead of blebbing, cells with depolymerized F-actin respond to pressure by detaching the plasma membrane from the cytoskeleton underneath. On the other hand, the compression force of keratinocytes expressing a mutated keratin (cell line, KEB-7) is 1.6-2.2 times less than that for the control cell line that has normal keratin networks. Therefore, we infer that the keratin intermediate filament network is responsible for the extremely high keratinocyte stiffness and resilience. This could manifest into the rugged protective nature of the human epidermis.

Single cell mechanics of keratinocyte cells.

Cellular directional migration in an electric field (galvanotaxis) is one of the mechanisms guiding cell movement in embryogenesis and in skin epidermal repair. The epithelial sodium channel (ENaC), in addition to its function of regulating sodium transport in kidney, has recently been found to modulate cell locomotory speed. Here we tested whether ENaC has an additional function of mediating the directional migration of galvanotaxis in keratinocytes. Genetic depletion of ENaC completely blocks only galvanotaxis and does not decrease migration speed. Overexpression of ENaC is sufficient to drive galvanotaxis in otherwise unresponsive cells. Pharmacologic blockade or maintenance of the open state of ENaC also decreases or increases, respectively, galvanotaxis, suggesting that the channel open state is responsible for the response. Stable lamellipodial extensions formed at the cathodal sides of wild-type cells at the start of galvanotaxis; these were absent in the ENaC knockout keratinocytes, suggesting that ENaC mediates galvanotaxis by generating stable lamellipodia that steer cell migration. We provide evidence that ENaC is required for directional migration of keratinocytes in an electric field, supporting a role for ENaC in skin wound healing.

The epithelial sodium channel mediates the directionality of galvanotaxis in human keratinocytes.

Murine keratinocyte culture from neonatal skin is an important tool for studying the functional role of specific genes in epithelial biology. However, when the transgenic animal is only available in a geographically distant local, obtaining viable keratinocytes can be problematic. A method for transferring the isolated murine skin from collaborating labs could decrease the cost of shipping live animals, and would allow the efficient use of the tissues from the transgenic animals. Here we optimized shipping conditions and characterized the cells retrieved and cultured from mouse skin shipped for 48 hours at 0°C. The cultured keratinocytes from the control, non-shipped skin and the 2-day shipped skin were 43.6 +/- 7.8% viable, doubled every 2 days, and expressed comparable amounts of heat shock proteins and CD29/integrin beta-1. However, under the same shipping conditions, the 3-day shipped tissue failed to establish colonies in the culture. Therefore, this 2-day shipping technique allows the transfer mouse skin from distant locations with recovery of viable, propagatable keratinocytes, facilitating long-distance collaborations. J. Cell. Physiol. © 2014 Wiley Periodicals, Inc.

Article	Year
MEI-1/katanin is required for translocation of the meiosis I spindle to the oocyte cortex in C elegans. Developmental biology\| PubMed ID: 12885567	2003
Kinesin-1 mediates translocation of the meiotic spindle to the oocyte cortex through KCA-1, a novel cargo adapter. The Journal of cell biology\| PubMed ID: 15883196	2005
Single cell mechanics of keratinocyte cells. Ultramicroscopy\| PubMed ID: 20728993	2010
The epithelial sodium channel mediates the directionality of galvanotaxis in human keratinocytes. Journal of cell science\| PubMed ID: 23447677	2013
Recovery and cultivation of keratinocytes from shipped mouse skin. Journal of cellular physiology\| PubMed ID: 25160898	2014

Hsin-ya Yang

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