Crossing over during Caenorhabditis elegans meiosis requires a conserved MutS-based pathway that is partially dispensable in budding yeast.
Formation of crossovers between homologous chromosomes during Caenorhabditis elegans meiosis requires the him-14 gene. Loss of him-14 function severely reduces crossing over, resulting in lack of chiasmata between homologs and consequent missegregation. Cytological analysis showing that homologs are paired and aligned in him-14 pachytene nuclei, together with temperature-shift experiments showing that him-14 functions during the pachytene stage, indicate that him-14 is not needed to establish pairing or synapsis and likely has a more direct role in crossover formation. him-14 encodes a germline-specific member of the MutS family of DNA mismatch repair (MMR) proteins. him-14 has no apparent role in MMR, but like its Saccharomyces cerevisiae ortholog MSH4, has a specialized role in promoting crossing over during meiosis. Despite this conservation, worms and yeast differ significantly in their reliance on this pathway: whereas worms use this pathway to generate most, if not all, crossovers, yeast still form 30-50% of their normal number of crossovers when this pathway is absent. This differential reliance may reflect differential stability of crossover-competent recombination intermediates, or alternatively, the presence of two different pathways for crossover formation in yeast, only one of which predominates during nematode meiosis. We discuss a model in which HIM-14 promotes crossing over by interfering with Holliday junction branch migration.
Zalevsky
J
J
Department of Developmental Biology and Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA.
MacQueen
A J
AJ
Duffy
J B
JB
Kemphues
K J
KJ
Villeneuve
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D020137:Base Pair Mismatch; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics; D002467:Cell Nucleus / Q000502:physiology; D017124:Conserved Sequence; D003434:Crossing Over, Genetic; D004260:DNA Repair; D004268:DNA-Binding Proteins; D005260:Female; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008540:Meiosis / Q000235:genetics*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D015801:Helminth Proteins; C401307:Him-14 protein, C elegans; C091158:MSH4 protein, S cerevisiae; C409221:MSH4 protein, human; D029701:Saccharomyces cerevisiae Proteins