Physical Manipulation to Generate <em>Xenopus</em> Mini Embryos

A defining characteristic of early embryogenesis is the rapid, exponential decrease in individual cell size while the overall embryo volume remains constant. The nucleocytoplasmic (N:C) ratio plays a critical role in regulating cellular and molecular activities essential to early embryogenesis. Physical manipulation of the embryo size, therefore, represents an important way of investigating these developmental mechanisms. The large size (~ 1.2 mm in diameter) and high developmental plasticity of Xenopus laevis early embryos make them an ideal model for physical dissection and manipulation to interrogate the regulatory mechanisms of development. Here, we describe an approach for generating mini embryos with altered cytoplasmic volume and N:C ratio by constricting 1-cell Xenopus laevis embryos with hair knots. The resulting mini embryos have been shown to initiate early zygotic genome activation (ZGA) directly induced by cell size reduction and N:C ratio growth. These mini embryos, which can be generalized to other embryonic systems, therefore provide a unique, powerful tool for dissecting size-mediated mechanisms of early embryo development.