In vivo staining of mouse preimplantation embryos with Hoechst 33342

Female mice bearing secondary oocytes or preimplantation embryos of various stages were injected with Hoechst 33342 (H 33342), either intravenously or intraperitoneally and sacrificed at various intervals afterward. The dye penetrated through the wall of oviduct and stained the nuclei of its cells as well as mitotic chromosomes of secondary oocytes, the pronuclei of one-cell embryos, and nuclei of blastomeres and polar bodies. The nuclear fluorescence was observed in living cells flushed out of the oviduct as well as in those fixed in oviduct, embedded in paraffin, and sectioned. H 33342 injected in a dose of 10 micrograms/g of body weight failed to interfere with preimplantation development of stained embryos as indicated by the number of blastocysts per mouse and number of cells per blastocyst.