Staging mouse preimplantation development in vivo using optical coherence microscopy

In mammals, preimplantation development primarily occurs in the oviduct (or fallopian tube) where fertilized oocytes migrate through, develop and divide as they prepare for implantation in the uterus. Studies of preimplantation development currently rely on ex vivo experiments with the embryos cultured outside of the oviduct, neglecting the native environment for embryonic growth. This prevents the understanding of the natural process of preimplantation development and the roles of the oviduct in early embryonic health. Here, we report an in vivo optical imaging approach enabling high-resolution visualizations of developing embryos in the mouse oviduct. By combining optical coherence microscopy (OCM) and a dorsal imaging window, the subcellular structures and morphologies of unfertilized oocytes, zygotes and preimplantation embryos can be well resolved in vivo, allowing for the staging of development. We present the results together with bright-field microscopy images to show the comparable imaging quality. As the mouse is a well-established model with a variety of genetic engineering strategies available, the in vivo imaging approach opens great opportunities to investigate how the oviduct and early embryos interact to prepare for successful implantation. This knowledge could have beneficial impact on understanding infertility and improving in vitro fertilization. OCM through a dorsal imaging window enables high-resolution imaging and staging of mouse preimplantation embryos in vivo in the oviduct.