Altered development of Xenopus embryos in a hypogeomagnetic field.

The hypogeomagnetic field (HGMF; magnetic fields <200 nT) is one of the fundamental environmental factors of space. However, the effect of HGMF exposure on living systems remains unclear. In this article, we examine the biological effects of HGMF on the embryonic development of Xenopus laevis (African clawed frog). A decrease in horizontal third cleavage furrows and abnormal morphogenesis were observed in Xenopus embryos growing in the HGMF. HGMF exposure at the two-cell stage, but no later than the four-cell stage, is enough to alter the third cleavage geometry pattern. Immunofluorescent staining for α-tubulin showed reorientation of the spindle of four-cell stage blastomeres. These results indicate that a brief (2-h) exposure to HGMF is sufficient to interfere with the development of Xenopus embryos at cleavage stages. Also, the mitotic spindle could be an early sensor to the deprivation of the geomagnetic field, which provides a clue to the molecular mechanism underlying the morphological and other changes observed in the developing and/or developed embryos.