アフリカツメガエルの卵割球RNAによる速やかな前核形成

The small hypercondensed sperm nucleus undergoes a dramatic transformation into a large round pronucleus with relaxed chromatin during the brief cleavage period in metazoan embryos, enabling the activation of chromatin functions necessary for subsequent development. However, it remains unclear whether the egg cytoplasm-specific physicochemical properties play a role in pronucleus assembly. Here, we evaluated the impact of abundant RNAs in eggs on pronucleus assembly in Xenopus laevis cell-free reconstitution system. We found that the introduction of RNAs at an appropriate concentration led to a rapid nuclear growth, more dispersed chromatin distribution, and dissociation of sperm-specific nuclear proteins from the chromatin. These chromatin remodeling properties, which were reproducible through introduction of negatively charged compounds, facilitated the incorporation of somatic histones into chromatin in the reconstituted nuclei. Based on these findings, we propose that the remodeled chromatin by negatively charges of cytoplasmic RNAs accelerates rapid decondensation of negatively charged chromatin and pronucleus assembly during the brief cleavage period following fertilization.