Reconstruction of mammoth nuclei upon nuclear transfer to mouse oocytes. (a) Immunostaining of nucleus-like structure from elephant or mammoth tissue with anti-histone H3, anti-lamin B2 and DAPI. (b) Experimental scheme and conditions for NT and imaging. Mouse metaphase II oocytes were injected with mixture of various fluorescent probes, subjected to NT without enucleation of metaphase II chromosomes and imaged. (c–h) Time-lapse images of NT oocytes injected with mammoth (d,f,g and h) or elephant (c and e) nuclei at the stages of before (c,d and g) and after (e,f and h) activation. Green and red colours represent EB1 (spindle) and H2B (chromatin), respectively. White colour represents H2B-mCherry signal (e and f). Yellow arrows indicate mammoth or elephant nucleus-like structures (c and d) and the mammoth chromosome that detached from nucleus-like structure and entered into the mouse pronucleus (g and h). Arrowheads indicate the injected mammoth or elephant nucleus forming pronucleus-like structures (nuclear blebs). Asterisks show metaphase II chromosomes. eSCN, mSCN and fPN represent elephant somatic cell nucleus, mammoth somatic cell nucleus and female pronucleus, respectively. The time (h:min) shown in the images indicates time duration from the starting point of imaging. Bar = 10 μm.