Cell Counting Techniques for Preimplantation Mouse Embryos Using Fluorescent DNA Dyes

Counting cells in preimplantation embryos by light microscopy is straightforward until morula compaction, when cell boundaries in living embryos become indistinct. An alternative to morphological assessment of cell number is to use fluorescent DNA dyes. This protocol details simple nuclear counting with a single DNA dye (Hoechst) or a more complicated procedure in which differential nuclear counts of the trophectoderm and inner cell mass (ICM) can be made using immunosurgery of the blastocyst and two DNA dyes (Hoechst and propidium iodide).