Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome Segregation in Mammalian Meiosis Yong-Hyun Shin1,2., Youngsok Choi3., Serpil Uckac Erdin1, Svetlana A. Yatsenko 4 , Malgorzata Kloc5, Fang Yang 6 , P. Jeremy Wang 6 , Marvin L. Meistrich7, Aleksandar Rajkovic1,2* 1 Department of Obstetrics and Gynecology, Baylor College of Medicine, Houston, Texas, United States of America, 2 Department of Obstetrics and Gynecology and Reproductive Sciences, Magee Women’s Research Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 3 Fertility Center of CHA General Hospital, CHA Research Institute, CHA University, Seoul, Korea, 4 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America, 5 Department of Surgery, The Methodist Hospital and The Methodist Hospital Research Institute, Houston, Texas, United States of America, 6 Department of Animal Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 7 Department of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America Abstract Meiosis is unique to germ cells and essential for reproduction. During the first meiotic division, homologous chromosomes pair, recombine, and form chiasmata. The homologues connect via axial elements and numerous transverse filaments to form the synaptonemal complex. The synaptonemal complex is a critical component for chromosome pairing, segregation, and recombination. We previously identified a novel germ cell–specific HORMA domain encoding gene, Hormad1, a member of the synaptonemal complex and a mammalian counterpart to the yeast meiotic HORMA domain protein Hop1. Hormad1 is essential for mammalian gametogenesis as knockout male and female mice are infertile. Hormad1 deficient (Hormad12/2) testes exhibit meiotic arrest in the early pachytene stage, and synaptonemal complexes cannot be visualized by electron microscopy. Hormad1 deficiency does not affect localization of other synaptonemal complex proteins, SYCP2 and SYCP3, but disrupts homologous chromosome pairing. Double stranded break formation and early recombination events are disrupted in Hormad12/2 testes and ovaries as shown by the drastic decrease in the cH2AX, DMC1, RAD51, and RPA foci. HORMAD1 co-localizes with cH2AX to the sex body during pachytene. BRCA1, ATR, and cH2AX co-localize to the sex body and participate in meiotic sex chromosome inactivation and transcriptional silencing. Hormad1 deficiency abolishes cH2AX, ATR, and BRCA1 localization to the sex chromosomes and causes transcriptional de-repression on the X chromosome. Unlike testes, Hormad12/2 ovaries have seemingly normal ovarian folliculogenesis after puberty. However, embryos generated from Hormad12/2 oocytes are hyper- and hypodiploid at the 2 cell and 8 cell stage, and they arrest at the blastocyst stage. HORMAD1 is therefore a critical component of the synaptonemal complex that affects synapsis, recombination, and meiotic sex chromosome inactivation and transcriptional silencing. Citation: Shin Y-H, Choi Y, Uckac Erdin S, Yatsenko SA, Kloc M, et al. (2010) Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome Segregation in Mammalian Meiosis. PLoS Genet 6(11): e1001190. doi:10.1371/journal.pgen.1001190 Editor: R. Scott Hawley, Stowers Institute for Medical Research, United States of America Received April 3, 2010; Accepted September 30, 2010; Published November 4, 2010 Copyright: 2010 Shin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported in part by the National Institutes of Health Grant HD054829 to AR (http://grants.nih.gov/grants/oer.htm). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: rajkovic@upmc.edu . These authors contributed equally to this work. Introduction Mammalian meiosis is unique to germ cells and a critical step in sexual reproduction. Meiosis reduces the chromosome comple- ment to haploidy in preparation for fertilization. The first meiotic division is unique in pairing of homologous chromosomes, homologous recombination, and formation of chiasmata. The reduction in chromosome numbers happens when homologous chromosomes segregate to opposite poles during the first meiotic division. Proper disjunction (separation) requires crossovers (manifested cytologically as chiasmata). The sister chromatids organize along structures called axial elements (AEs) and transverse elements connect AEs to form the synaptonemal complex (SC) [1]. SC is a proteinaceous structure that connects paired homologous chromosomes during prophase I of meiosis, and SC is critical for wild-type levels of crossovers to occur during meiosis. AEs are critical part of the SCs and mutations in proteins that form AEs disrupt sister chromatid cohesion, recombination, and chromosome segregation [2–4]. Proteins with HORMA domain are critical components of the axial elements [5]. HORMA domain proteins are predicted to form globular structure that may sense specialized chromatin states, such as those associated with double strand breaks (DSBs) or other forms of DNA damage [5]. Several mammalian proteins that contain HORMA domain, such as mitotic arrest deficient protein 2, MAD2, are essential for mitosis [6–7]. Mice lacking MAD2 unsurprisingly die during early embryogenesis [7]. In lower organisms, several meiotic specific HORMA proteins are known PLoS Genetics | www.plosgenetics.org 1 November 2010 | Volume 6 | Issue 11 | e1001190