Figure 2

The Synaptonemal Complex. The Synaptonemal Complex (SC) is a meiosis-specific supra-molecular protein assembly that supports synapsis of homologs, crossover/chiasma formation and reciprocal recombination between sister chromatids at the Pachytene stage of Meiosis I. The chromatids of each homolog are held together by the Lateral Element (LE) consisting of cohesin proteins, formed already at the earlier Leptotene stage and then called the Axial Element [150]. The LE holds the two chromatids of each homolog tightly together until the onset of Anaphase I (see Fig 1). The central Element (CE) of the SC, made up of additional meiosis-specific proteins that hold the homologs together in a Velcro type of fashion, is required for maturation of early recombination events into crossovers/chiasmata [153]. (a) Electron-microscopy picture of the SC from a human male showing the Lateral Elements (LE) holding the two chromatids of each homolog together, the Central Element (CE), and the surrounding chromatin loops. Courtesy of N. Saadallah. (b) Schematic illustration showing the Lateral Elements (green), the Central Element, consisting of transverse fibrils (red), and the surrounding Chromatin (blue). (c) Electron-microscopy picture of the same bivalent as in (a) focused in such a way that the Late Recombination Nodules, corresponding to the crossovers/chiasmata are highlighted (arrows). The telomeres at each end, forming so-called attachment plaques, are associated with the nuclear membrane. Courtesy of N. Saadallah. Revised from [3].