  Galvanotaxis is believed to be driven by the redistribution of transmembrane
proteins and other molecules, referred to as "sensors", through electrophoresis
and electroosmosis. Here, we update our previous model of the limits of
galvanotaxis due to stochasticity of sensor movements to account for cell shape
and orientation. Computing the Fisher information, we find that cells in
principle possess more information about the electric field direction when
their long axis is parallel to the field, but that for weak fields
maximum-likelihood estimators of the field direction may actually have lower
variability when the cell's long axis is perpendicular to the field. In an
alternate possibility, we find that if cells instead estimate the field
direction by taking the average of all the sensor locations as its directional
cue ("vector sum"), this introduces a bias towards the short axis, an effect
not present for isotropic cells. We also explore the possibility that cell
elongation arises downstream of sensor redistribution. We argue that if sensors
migrate to the cell's rear, the cell will expand perpendicular the field - as
is more commonly observed - but if sensors migrate to the front, the cell will
elongate parallel to the field.
