Cortex reorganization of Xenopus laevis eggs in strong static magnetic fields.

Daniel Mietchen,Jörg W Jakobi,Hans-Peter Richter

doi:10.1186/1477-044x-3-2

Abstract

Observations of magnetic field effects on biological systems have often been contradictory. For amphibian eggs, a review of the available literature suggests that part of the discrepancies might be resolved by considering a previously neglected parameter for morphological alterations induced by magnetic fields – the jelly layers that normally surround the egg and are often removed in laboratory studies for easier cell handling. To experimentally test this hypothesis, we observed the morphology of fertilizable Xenopus laevis eggs with and without jelly coat that were subjected to static magnetic fields of up to 9.4 T for different periods of time. A complex reorganization of cortical pigmentation was found in dejellied eggs as a function of the magnetic field and the field exposure time. Initial pigment rearrangements could be observed at about 0.5 T, and less than 3 T are required for the effects to fully develop within two hours. No effect was observed when the jelly layers of the eggs were left intact. These results suggest that the action of magnetic fields might involve cortical pigments or associated cytoskeletal structures normally held in place by the jelly layers and that the presence of the jelly layer should indeed be included in further studies of magnetic field effects in this system.

Highlights

The molecular processes governing the action of static magnetic fields on living systems remain poorly understood, partly because the experimental evidence is equivocal
The results reveal that the Tennis Ball Effect (TBE) II frequency depends on exposure time in a sigmoidal way and that a critical threshold just above 1 T is required for TBE II to occur, while all groups exposed to field strengths above 3 T reached essentially the same TBE II percentage after 76 min of exposure to the field
The occurence of TBE in all fertilizable eggs without jelly coat (JC) at higher field strengths points at a passive reaction to the magnetic field and suggests the involvement of structures or pathways in the oocyte that are not present before maturation and normally kept in place by the JC

Summary

Introduction

The molecular processes governing the action of static magnetic fields on living systems remain poorly understood, partly because the experimental evidence is equivocal (reviewed in [1,2]). As for amphibian development, the hatching rate of embryos of the frog Rana pipiens subjected to the field of a 1 T permanent magnet was found to be reduced [3]. This stimulated further studies in the frog Xenopus laevis whose giant eggs with a diameter of about 1.3 mm have rendered it a popular model system [4,5]. The JC serves multiple functions, one of which is to glue the eggs to their substrate [4,5] As this complicates (page number not for citation purposes)

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