COVER: Representative images of nuclei of in vitro fertilized (IVF, orange-highlighted area) and somatic cell nuclear transfer (SCNT, blue-highlighted area) embryos at the 1-cell stage, whose nuclear actin is visualized with nuclear actin chromobody-green fluorescent protein, a nuclear actin probe (top panels). Pronuclei of IVF zygotes mostly possess interconnected filamentous actin (F-actin). In contrast, nuclei of SCNT embryos have different types of nuclear actin filaments, as exemplified by thick actin filament and dot-like aggregates. Thus, these images show that abnormal actin nucleoskeleton structures are formed in SCNT embryos. Embryos were fixed during 8-9 hours post insemination for IVF or 8-9 hours post activation for SCNT, and DNA was stained with DAPI. Scale bars, 5 μm. Shindo T., Ihashi S., Sakamoto Y., Okuno T., Tomikawa J., Miyamoto K. (2021) Visualization of endogenous nuclear F-actin in mouse embryos reveals abnormal actin assembly after somatic cell nuclear transfer, J. Biochem. 169, 303-311