Zygote arrest 1 (Zar1) is a novel maternal-effect gene critical for the oocyte-to-embryo transition.

Document Type


Publication Date



Animal, Blotting-Northern, Blotting-Southern, Blotting-Western, Cloning-Molecular, Comparative-Study, DNA-Replication, Egg-Proteins, Embryo, Female, Fertility, Fertilization-in-Vitro, Gene-Expression-Regulation, Gene-Library, Goats, In-Vitro, Meiosis, Mice, Mice-Inbred-C57BL, Molecular-Sequence-Data, Oocytes, Pregnancy, RNA-Messenger, Reverse-Transcriptase-Polymerase-Chain-Reaction, Sequence-Homology-Amino-Acid, Spermatids, Stem-Cells, SUPPORT-NON-U-S-GOVT, SUPPORT-U-S-GOVT-P-H-S, Zygote

JAX Source

Nat Genet 2003 Feb; 33(2):187-191.


The female gamete (the oocyte) serves the distinct purpose of transmitting the maternal genome and other maternal factors that are critical for post-ovulation events. Through the identification and characterization of oocyte-specific factors, we are beginning to appreciate the diverse functions of oocytes in ovarian folliculogenesis, fertilization and embryogenesis. To understand these processes further, we identified genes called zygote arrest 1 (Zar1 and ZAR1 in mouse and human, respectively) as novel oocyte-specific genes. These encode proteins of 361 amino acids and 424 amino acids, respectively, which share 59% amino-acid identity and an atypical plant homeo-domain (PHD) motif. Although Zar1-null (Zar1(-/-)) mice are viable and grossly normal, Zar1(-/-) females are infertile. Ovarian development and oogenesis through the early stages of fertilization are evidently unimpaired, but most embryos from Zar1(-/-) females arrest at the one-cell stage. Distinct pronuclei form and DNA replication initiates, but the maternal and paternal genomes remain separate in arrested zygotes. Fewer than 20% of the embryos derived from Zar1(-/-) females progress to the two-cell stage and show marked reduction in the synthesis of the transcription-requiring complex, and no embryos develop to the four-cell stage. Thus, Zar1 is the first identified oocyte-specific maternal-effect gene that functions at the oocyte-to-embryo transition and, as such, offers new insights into the initiation of embryonic development and fertility control in mammals.