title: Absence of SUN-domain protein Slp1 blocks karyogamy and switches meiotic recombination and synapsis from homologs to sister chromatids.
abstract: Karyogamy, the process of nuclear fusion is required for two haploid gamete nuclei to form a zygote. Also, in haplobiontic organisms, karyogamy is required to produce the diploid nucleus/cell that then enters meiosis. We identify sun like protein 1 (Slp1), member of the mid-Sad1p, UNC-84-domain ubiquitous family, as essential for karyogamy in the filamentous fungus Sordaria macrospora, thus uncovering a new function for this protein family. Slp1 is required at the last step, nuclear fusion, not for earlier events including nuclear movements, recognition, and juxtaposition. Correspondingly, like other family members, Slp1 localizes to the endoplasmic reticulum and also to its extensions comprising the nuclear envelope. Remarkably, despite the absence of nuclear fusion in the slp1 null mutant, meiosis proceeds efficiently in the two haploid "twin" nuclei, by the same program and timing as in diploid nuclei with a single dramatic exception: the normal prophase program of recombination and synapsis between homologous chromosomes, including loading of recombination and synaptonemal complex proteins, occurs instead between sister chromatids. Moreover, the numbers of recombination-initiating double-strand breaks (DSBs) and ensuing recombinational interactions, including foci of the essential crossover factor Homo sapiens enhancer of invasion 10 (Hei10), occur at half the diploid level in each haploid nucleus, implying per-chromosome specification of DSB formation. Further, the distribution of Hei10 foci shows interference like in diploid meiosis. Centromere and spindle dynamics, however, still occur in the diploid mode during the two meiotic divisions. These observations imply that the prophase program senses absence of karyogamy and/or absence of a homolog partner and adjusts the interchromosomal interaction program accordingly.
authors.affiliation: Institut de Génétique et Microbiologie, Unité Mixte de Recherche 8621, Université Paris-Sud, 91405 Orsay, France;
authors.forename: Christelle
authors.initials: C
authors.lastname: Vasnier
authors.affiliation: Institut de Génétique et Microbiologie, Unité Mixte de Recherche 8621, Université Paris-Sud, 91405 Orsay, France; Institut Curie, 75248 Paris Cedex 05, France; and.
authors.forename: Arnaud
authors.initials: A
authors.lastname: de Muyt
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138.
authors.forename: Liangran
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Institut de Génétique et Microbiologie, Unité Mixte de Recherche 8621, Université Paris-Sud, 91405 Orsay, France;
authors.forename: Sophie
authors.initials: S
authors.lastname: Tessé
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138 denise.zickler@igmors.u-psud.fr eric.espagne@igmors.u-psud.fr kleckner@fas.harvard.edu.
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Kleckner
authors.affiliation: Institut de Génétique et Microbiologie, Unité Mixte de Recherche 8621, Université Paris-Sud, 91405 Orsay, France; denise.zickler@igmors.u-psud.fr eric.espagne@igmors.u-psud.fr kleckner@fas.harvard.edu.
authors.forename: Denise
authors.initials: D
authors.lastname: Zickler
authors.affiliation: Institut de Génétique et Microbiologie, Unité Mixte de Recherche 8621, Université Paris-Sud, 91405 Orsay, France; denise.zickler@igmors.u-psud.fr eric.espagne@igmors.u-psud.fr kleckner@fas.harvard.edu.
authors.forename: Eric
authors.initials: E
authors.lastname: Espagne
mesh_terms: D002842:Chromatids / Q000235:genetics / Q000378:metabolism*; D023902:Chromosome Pairing / Q000502:physiology*; D015825:Chromosomes, Fungal / Q000235:genetics / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006238:Haploidy; D009685:Nuclear Envelope / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic / Q000502:physiology*; D020037:Sordariales / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins
keywords: recombination/synapsis; sisters versus homologs