The oocyte-early embryo-specific subcortical maternal complex in mammals

Prior to zygotic genome activation, gene transcription is quiescent. The programs of the early embryonic development are mainly regulated by maternal-effect genes. The research of mammalian maternal-effect genes has long been hindered due to the limitation of research materials and techniques. Recently, a subcortical maternal complex (SCMC) was identified specifically in mammalian oocytes and preimplantation embryos. The SCMC is a protein complex consisting of numerous maternal effect proteins, and is required for mouse preimplantation development. Accumulating evidence suggests that SCMC can be used to identify new maternal-effect genes, to clarify the molecular mechanism of other maternal-effect genes, and to explore the regulation of early embryonic development in mammals. Additionally, the SCMC may be conserved in human oocytes and early embryos. Importantly, the mutations of human SCMC genes are associated with several human reproductive disorders. Collectively, these findings indicate that the SCMC may be an important module orchestrating the maternal-to-zygotic transition in mammalian early development. Further investigations of the SCMC will greatly promote the understanding of molecular regulation in mammalian early development, significantly contributing to human reproductive medicine.