期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：38
页码：E4015-E4023
DOI：10.1073/pnas.1415758111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMeiosis is the specialized cellular program that generates gametes for sexual reproduction. In the fungus Sordaria macrospora karyogamy is required to produce the diploid cell that enters the meiotic program. In absence of the mid-Sad1p, UNC-84-domain sun like protein 1, karyogamy does not occur. Meiosis nonetheless proceeds efficiently in the two haploid nuclei, but with the entire program of interhomolog events now occurring instead between sister chromatids, including spatially patterned recombination and synaptonemal complex formation. As a result, significant levels of gametes are still formed. In contrast, other cases of meiosis in haploid genome complements exhibit inefficient or aberrant chromosomal programs. We thus propose that Sordaria can sense the absence of karyogamy so as to trigger an appropriately regular response. 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.
关键词：sisters versus homologs ; recombination/synapsis
