Abstract
The synaptonemal complex is a multiprotein complex, which mediates the synapsis and recombination between homologous chromosomes during meiosis. The complex is comprised of two lateral elements and a central element connected by perpendicular transverse filaments (TFs). A 3D model based on actual morphological data of the SC is missing. Here, we applied electron tomography (ET) and manual feature extraction to generate a quantitative 3D model of the murine SC. We quantified the length (90 nm) and width (2 nm) of the TFs. Interestingly, the 80 TFs/µm are distributed asymmetrically in the central region of the SC challenging available models of SC organization. Furthermore, our detailed 3D topological analysis does not support a bilayered organization of the central region as proposed earlier. Overall, our quantitative analysis is relevant to understand the functions and dynamics of the SC and provides the basis for analyzing multiprotein complexes in their morphological context using ET.
Highlights
In mammals, transverse filaments (TFs) are formed by homodimers of SYCP1 (976 amino acids)[19] with SYCP1 molecules showing the same polarity
Polymerization studies of SYCP1 are consistent with the notion that the length of the coiled-coil is a primary determinant of synaptonemal complex (SC) width[22]
We have investigated the 3D ultrastructure of the murine SC by using electron tomography (ET)
Summary
TFs are formed by homodimers of SYCP1 (976 amino acids)[19] with SYCP1 molecules showing the same polarity. The two long α-helices of the SYCP1 dimer, which make up the bulk of the protein, form a coiled-coil structure (amino acids 101–783) connecting either one of the LEs with the CE16,20. Pushing the resolution of light microscopy beyond the limit of diffraction, techniques such as dSTORM enabled precise protein localization maps with nanometer resolution[33,34]. These super-resolution approaches lack the morphological context that EM techniques can provide. These data are of relevance in order to understand the functions and dynamics of the SC
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