Level of histone H4 mRNA in Xenopus laevis embryonic cells cultured in the absence of cell adhesion.

The amount of histone H4 mRNA per embryo was followed during early development of Xenopus laevis by Northern blot analyses using a cloned histone H4 cDNA as the probe. The H4 mRNA content was nearly constant until the blastula stage, increased greatly at the gastrula stage and then decreased at the neurula stage. Experiments with actinomycin D suggested that most H4 mRNA molecules detected at the late gastrula and neurula stages were maintained depending on new transcription of H4 genes during these stages. To see if the H4 mRNA level is affected by cell adhesion, we prepared dissociated cells and measured H4 mRNA content under conditions that inhibit cellular reaggregation. It was found that the amount of H4 mRNA per embryo in dissociated and reaggregation-inhibited cells was nearly equal to that of the control embryo at the neurula stage. Therefore, we conclude that the synthetic activity of histone H4 mRNA is not dependent on the cellular adhesion during development.