Lineage-specific expression of heterochromatin protein 1γ in post-compaction, in vitro-produced bovine embryos

Heterochromatin protein 1 gamma (HP1 gamma) is a highly conserved regulator of euchromatic and heterochromatic gene expression. Mammalian HP1 gamma is essential for both successful preimplantation embryo development and maintenance of pluripotency in embryonic stem cells in vitro. Here, we describe HP1 gamma protein localisation in matured (MII) bovine oocytes and IVF preimplantation embryos at defined developmental stages. HP1 gamma is expressed in post-compaction embryos in a highly lineage-specific pattern. In embryonic stages preceding the maternal to embryonic transition (MET), HP1 gamma protein was primarily cytoplasmic, whereas in 8-16-cell embryos (post MET), HP1 gamma was primarily nuclear. Lineage-specific patterns of HP1 gamma protein localisation become evident from compaction, being restricted to peripheral, extraembryonic cells at the morula and blastocyst stages (Days 7-9). Surprisingly, we detected HP1 gamma mRNA in both embryonic and extraembryonic cells in blastocysts by fluorescence in situ hybridisation. In trophectoderm cells, HP1 gamma protein was localised in specific patterns at the mitotic and interphase stages of the cell cycle. These results demonstrate lineage- and cell cycle-specific patterns of HP1 gamma protein localisation in the post-compaction, preimplantation bovine embryo and raise interesting questions about the role of HP1 gamma in early embryo development.