Correlation between the cell cycle in the neurectoderm and differentiation during the early development of Xenopus laevis. 1. BUdR sensitivity during gastrulation.

An hypothesis has been proposed by Holtzer and co-workers (1963, 1970, 1973) that the process of cell differentiation may be coupled in an obligatory manner with 'Quantal' cell cycle(s) which precede it. We have demonstrated that a 'wave' of DNA synthesis occurs in the neurectoderm of Xenopus laevis gastrula. This event of the cell cycle appears to be associated with the primary embryonic induction by the subjacent mesodermal tissue. The peak of DNA synthesis was observed in that area of the neurectoderm which was overlying the pre-chordal plate of mesoderm. Administration of 5-bromodeoxyuridine (BUdR) into the DNA of cells in a critical phase preceding overt differentiation, is known to perturb cytodifferentiation. In the present work sensitivity of X. laevis gastrula to BUdR (10(-3) M) has been investigated so as to assess the significance for neurogenesis of the wave of DNA synthesis in the neurectoderm.