Yonezawa, N.; Shindo, T.; Oda, H.; Kimura, H.; Hiraoka, Y.; Haraguchi, T.; Yamagata, K.

The cell nucleus is a dynamic structure repeating disassembly and reformation during mitosis. Reformation of the nucleus is essential for cell proliferation, and therefore, the factors required for nuclear reformation are fundamental for eukaryotes. Although various factors have been identified in in vitro systems using frog egg extracts and in vivo imaging of somatic cells, little is known about the factors required for the formation of functional nuclear structures in living mouse eggs. To identify such factors, we used a reconstruction approach to construct an artificial nucleus around DNA in mouse eggs. T4 phage DNA (166 kbp) was microinjected into living mouse oocytes. Amounts of DNA injected and injection timing were examined to determine the conditions appropriate for the formation of functional nuclei. Microinjection of 100-500 ng/ul DNA during metaphase through telophase of the second meiosis, but not the subsequent interphase, was important for the formation of artificial nucleus. This T4 DNA-derived artificial nucleus had the structure of nuclear lamina and nuclear pore complexes, and nuclear transport activity, similar to natural nuclei. These results suggest that exogenous DNA can form a functional nucleus in mouse oocytes, regardless of the sequence or the source of DNA.