SUMO Localizes to the Central Element of Synaptonemal Complex and Is Required for the Full Synapsis of Meiotic Chromosomes in Budding Yeast

Abstract

The synaptonemal complex (SC) is a widely conserved structure that mediates the intimate alignment of homologous chromosomes during meiotic prophase and is required for proper homolog segregation at meiosis I. However, fundamental details of SC architecture and assembly remain poorly understood. The coiled-coil protein, Zip1, is the only component whose arrangement within the mature SC of budding yeast has been extensively characterized. It has been proposed that the Small Ubiquitin-like MOdifier, SUMO, plays a role in SC assembly by linking chromosome axes with Zip1's C termini. The role of SUMO in SC structure has not been directly tested, however, because cells lacking SUMO are inviable. Here, we provide direct evidence for SUMO's function in SC assembly. A meiotic smt3 reduction-of-function strain displays reduced sporulation, abnormal levels of crossover recombination, and diminished SC assembly. SC structures are nearly absent when induced at later meiotic time points in the smt3 reduction-of-function background. Using Structured Illumination Microscopy we furthermore determine the position of SUMO within budding yeast SC structure. In contrast to previous models that positioned SUMO near Zip1's C termini, we demonstrate that SUMO lies at the midline of SC central region proximal to Zip1's N termini, within a subdomain called the “central element”. The recently identified SUMOylated SC component, Ecm11, also localizes to the SC central element. Finally, we show that SUMO, Ecm11, and even unSUMOylatable Ecm11 exhibit Zip1-like ongoing incorporation into previously established SCs during meiotic prophase and that the relative abundance of SUMO and Ecm11 correlates with Zip1's abundance within SCs of varying Zip1 content. We discuss a model in which central element proteins are core building blocks that stabilize the architecture of SC near Zip1's N termini, and where SUMOylation may occur subsequent to the incorporation of components like Ecm11 into an SC precursor structure.

E3 ligase Hei10: a multifaceted structure-based signaling molecule with roles within and beyond meiosis

“…SUMO-GFP is still present after SC disassembly and during the diffuse stage as a cloud of dots and remains as a faint nuclear staining from diplotene to metaphase I (data not shown). SUMO localization along SCs is absent in sme4D, which does not form SCs, in agreement with the suggested role of SUMO in SC formation (e.g., Voelkel-Meiman et al 2013). SUMOylation is not observed in prominent foci along the SCs (Fig.…”

Synaptonemal Complex Proteins of Budding Yeast Define Reciprocal Roles in MutSγ-Mediated Crossover Formation

“…SUMOylated and unSUMOylated Ecm11, and (by extension) the Ecm11-interacting protein Gmc2, are components of the central element substructure, which assembles close to Zip1's N termini within the mature budding yeast SC Voelkel-Meiman et al 2013). In stark contrast to the reduced meiotic recombination frequencies observed in strains missing any of several other proteins required for SC assembly in budding yeast, such as zip1, zip2, zip4, and spo16 mutants (Sym and Roeder 1994;Chua and Roeder 1998;Borner et al 2004;Tsubouchi et al 2006;Shinohara et al 2008; VoelkelMeiman et al 2015), we discovered that meiotic interhomolog Map distances and interference values were calculated using tetrad analysis as described previously (Voelkel-Meiman et al 2015).…”

“…In budding yeast and in many other organisms, a "central element" substructure lies at the midline of the SC (Hamer et al 2006;Voelkel-Meiman et al 2013). SUMOylated and unSUMOylated Ecm11, and (by extension) the Ecm11-interacting protein Gmc2, are components of the central element substructure, which assembles close to Zip1's N termini within the mature budding yeast SC Voelkel-Meiman et al 2013).…”

Superresolution expansion microscopy reveals the three-dimensional organization of theDrosophilasynaptonemal complex

“…Mammals, particularly rat and mouse, also are thought to have a multilayered SC, although the structure is not as well defined as the lattice structure assembled in Blaps (5,7,8). In yeast, some SC components are added at a faster rate than they are turned over, suggesting that yeast also may have some layering of SC components (9,10). Finally, in flies, electron microscopy (EM) serial reconstructions have suggested that the SC may have multiple layers (5,11,12), although attempts to elucidate its 3D structure have thus far been inconclusive.…”

“…Although recent work using superresolution technologies such as structured illumination microscopy (SIM) and stochastic optical reconstruction microscopy (STORM) has provided additional information about SC structure (8,10,20), we are nearing the limit of what even superresolution microscopy methods can reveal about the detailed structure of this crucial complex. One solution to this impasse is to increase the size of the complex itself.…”