Nuclear fusion during yeast mating occurs by a three-step pathway.
In Saccharomyces cerevisiae, mating culminates in nuclear fusion to produce a diploid zygote. Two models for nuclear fusion have been proposed: a one-step model in which the outer and inner nuclear membranes and the spindle pole bodies (SPBs) fuse simultaneously and a three-step model in which the three events occur separately. To differentiate between these models, we used electron tomography and time-lapse light microscopy of early stage wild-type zygotes. We observe two distinct SPBs in approximately 80% of zygotes that contain fused nuclei, whereas we only see fused or partially fused SPBs in zygotes in which the site of nuclear envelope (NE) fusion is already dilated. This demonstrates that SPB fusion occurs after NE fusion. Time-lapse microscopy of zygotes containing fluorescent protein tags that localize to either the NE lumen or the nucleoplasm demonstrates that outer membrane fusion precedes inner membrane fusion. We conclude that nuclear fusion occurs by a three-step pathway.
Melloy
Patricia
P
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Shen
Shu
S
White
Erin
E
McIntosh
J Richard
JR
Rose
Mark D
MD
D002459:Cell Fusion; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D003227:Conjugation, Genetic; D036681:Fluorescence Recovery After Photobleaching / Q000379:methods; D005656:Fungal Proteins / Q000378:metabolism / Q000648:ultrastructure; D018715:Microscopy, Video; D008954:Models, Biological; D009685:Nuclear Envelope / Q000378:metabolism / Q000648:ultrastructure; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure
D005656:Fungal Proteins