Simple live-imaging method for viewing the first cleavage of mouse embryos that does not require genetic manipulation

Abstract

Time-lapse incubators have become increasingly popular in assisted reproductive technology, allowing for the observation of the developmental process, which may be useful in the selection of human embryos suitable for transplantation. Dynamic morphological changes of chromosomes and the cytoskeleton occur during early embryonic development, including in humans, and abnormalities such as embryonic chromosomal aneuploidy occur when development does not proceed normally. Chromosome and cytoskeletal dynamics are difficult to observe with time-lapse bright field monitoring. However, in recent years, live-cell imaging techniques have been used to analyse these dynamics by injecting fluorescently labelled cytoskeletal proteins or mRNA encoding fluorescein probes. These require complicated procedures and necessitate mechanical invasion of cells. Here, we introduced a fluorescence-labelled probe with cell-membrane permeability that specifically adheres to DNA and to the cytoskeleton as imaged in an incubator-integrated time-lapse confocal laser microscope observation system. This platform enabled us to analyse, in detail, the dynamics of chromosomes, microtubules, and microfilaments from the fertilized pronuclear zygote, through first cleavage, to 2-cell stage embryo. This method is simple and does not require genetic manipulation, and its application can be expected to provide novel insights into embryonic development in many mammals, including humans.