Control of Embryonic Pattern

ABSTRACT

Three-Dimensional Voltage Gradients Development Establishment of Embryonic Pattern
Riyi Shi and Richard B. Borgens, Center for Paralysis Research, Department of Basic Medical Sciences, School of Veterinary Medicine, Purdue University

We are interested in the generation of endogenous electrical fields associated with ionic currents driven through the vertebrate embryo by the transepithelial potential of its surface ectoderm. Using a non-invasive vibrating electrode for the measurement of ionic current, we have provided measurements of currents traversing amphibian embryos, and a preliminary report of the internal, extracellular voltage gradient under the neural plate which polarizes the embryo in the rostral/caudal axis (Metcalf et al. [1994] J. Exp. Zool. 268:307-322). Here we complete a description of this gradient in electrical potential (ca. 10 mV/mm, caudally negative), describe a simultaneous gradient organized in the medial/lateral axis (ca. 5-18 mV/mm, negative at the margins of the neural folds), and describe their appearance and disappearance during ontogeny of the axolotl embryo. Both voltage gradients are not expressed until neurulation, and disappearance at its climax. This appearance and disappearance correlates with the shunting of current out of the lateral margins of the neural folds in rostral regions of the embryo beginning at stage 15, and is not associated with a more substantial current leak from the blastopore which appears at gastrulation. A steady blastopore current is still present after neural tube formation when intra-embryonic electrical fields have been extinguished. We discuss the direct experimental tests supporting the hypothesis that these extracellular electrical fields both polarize the early vertebrate embryo and serve as cues for morphogenesis and pattern.
Developmental Dynamics 203: 456-467, 1995

Artist's reconstruction of the topology of electric fields in stage 15/16 embryos. This drawing attempts to insert the general form of subectodermal voltages within a mid-neurula amphibian embryo. This drawing helps show the relationship between the slope of internal voltages with external form of the neurula.

 

An outwardly directed ionic current, mark the location of limb development in the Avian and Murine limb

A.M. Altizer* L.J. Moriarty*, S.M. Bell^, C.M. Schreiner^, W.J. Scott^, R.B. Borgens*
*Center for Paralysis Research, School of Veterinary Medicine, Purdue University
^Children’s Hospital Research Foundation, Cincinnati, Ohio

In amphibians, an outwardly directed ionic current appears at the exact location of limb bud formation prior to its emergence in both urodeles and anurans (J. Exp. Zool. 228:491, 1983 and Dev. Biol. 79: 203, 1983). We have been interested if a similar outwardly directed current was associated with limb development in mouse and chick embryos where both genetic and molecular manipulation and examination of limb development are possible. Using a noninvasive vibrating electrode for the measurement of extrcellular current we have learned that an outwardly directed current is associated with limb development in the mouse embryo and the chick embryo. In the chick, we have developed a technique using a glass microelectrode inserted just beneath the ectoderm of the tail region – to reverse the direction of the prophetic ionic current at stage 13, prior to limb bud formation. We discuss the developmental responses to manipulation of limb bud currents in these species and the prospects of linking this developmental physiology to the signaling pathways that also appear to control limb primogenesis.