A small, physiological electric field orients cell division

Abstract

We report on an observation that the orientation of cell division is directed by small, applied electric fields (EFs). Cultured human corneal epithelial cells were exposed to a direct-current EF of physiological magnitude. Cells divided while attached to the culture dish, and most did so with a cleavage plane perpendicular to the EF vector. There are many instances in which cell divisions in vivo occur in the presence of direct-current physiological EF, for example, during embryonic morphogenesis, neuronal and epithelial differentiation, wound healing, or tumor formation. Endogenous physiological EFs may play important roles in some or all of these processes by regulating the axis of cell division and, hence, the positioning of daughter cells.

Figures

Figure 1

Two human corneal epithelial cells (arrow) dividing in an EF of 150 mV/mm. The field vector is horizontal, and cleavage occurred roughly perpendicular to the applied EF. The cells were a primary culture from donor cornea grown in DMEM/15% FBS.

Figure 2

Orientation of the cleavage plane of transformed human corneal epithelial cells also was affected by applied EFs (strength and polarity as shown). (a) No field control. Cleavage furrows are evident and oriented randomly. (b) Dividing cells in an applied EF showed preferential orientation of the cleavage furrow. The angle formed by the cleavage plane and the vector of the electric field was used to calculate the polarization of cleavage angle (for details see Materials and Methods). The cells were cultured in DMEM/F12 with 15% heat-inactivated FBS.

Figure 3

Angles of cleavage plane of transformed human corneal epithelial cells expressed as a polar diagram, where each symbol represents one cell. (a) Angles of cleavage plane of 415 dividing cells cultured without electric fields. (b) Polarized orientation of the cleavage plane of 443 cells dividing in a small physiological EF (in EFs for 20 hr in 5% CO2 incubator/37°C). Clearly, a high proportion of cells divided with a cleavage plane orthogonal to the EFs. (c) Polarized cleavage plane orientation of 18 dividing cells followed continuously in EF on the microscope stage. The total number of cells in each range of angles is indicated, both numerically and by compression of the symbols.

Figure 4

(a–k) Confocal optical sections of a dividing bovine corneal epithelial cell in an applied EF (at 150 mV/mm in DMEM/10% FBS). F-actin is concentrated at the cleavage plane (white arrowhead). Additionally, there is prominent accumulation of F-actin (red) and of TGFR II (green) at either poles of the two daughter cells (especially b–e). Although this segregation of F-actin and TGFR II to the two poles is evident, a nondividing cell beneath and two other nondividing cells (l) showed predominant accumulation of F-actin and TGFR II on the cathodal side. (m–o) Dividing cells (m and n) and nondividing cells (o) cultured without an applied EF are shown. Staining in both cases is more diffuse than for EF-treated cells, and, with the exception of some F-actin accumulation in the cleavage furrow, there was little polarization of F-actin or of TGFR II.