Bioelectrical controls of development: A role for the embryonic epithelium

Kevin Brian Hotary, Purdue University

Abstract

Bioelectric phenomena have been suggested to play a role in guiding a number of directional events during embryogenesis. In this study, some of the electrophysiological properties of developing Xenopus and chick embryos were studied. Extraembryonic measurements of currents driven through leaky epithelial regions were performed using a computer-assisted two-dimensional vibrating probe system. Intraembryonic measurements of electrical potentials generated by epithelia were performed using saline-filled microelectrodes. A potential was measured across the neural tube (which is derived from the ectodermal epithelium) of stage 21-25 Xenopus embryos, with the lumen being 18 mV negative to the interstitial spaces. Vibrating probe measurements on transected embryos suggest that this transneural tube potential is capable of driving a current. Potential measurements on stage 15-18 chick embryos suggest that their neural tube lumen is also negative to the interstitium, but only by 1 to 3 mV. Using the 2-D probe, large currents were found to leave the posterior intestinal portal (p.i.p.) of chick embryos during the period of tail gut reduction. Currents entered intact epithelial regions. These currents were first detected at stage 15, reached their maximum at stage 17, and declined to a very low level by stage 22. The currents, both inward and outward, were reduced by about 50% when Na$\sp{+}$ was replaced by choline in the bathing solution. The magnitude of currents leaving the p.i.p. suggested the existence of a measurable intraembryonic voltage gradient. Differences in the transepithelial potential between different regions of the embryo were used to calculate such a gradient. At stage 14 (before outward currents were detected), no voltage gradient was found. When the outward currents were maximum at stage 17, a voltage gradient as steep as 33 mV/mm was measured in the caudal end of the embryo. This is well above the level needed to affect cell migration in vitro. It is hypothesized that this endogenous field acts to guide neural crest migration in the developing chick.

Degree

Ph.D.

Advisors

Robinson, Purdue University.

Subject Area

Biology

COinS