Meiotic synapsis is the stable physical pairing of homologous chromosomes that begins in leptonema of prophase I and lasts until anaphase of prophase I. First, short segments of axial elements form along chromosomes. Telomeres then cluster at a region of the inner nuclear membrane and axial elements extend and fuse along the length of the chromosomes. Subsequent to the initiation of recombination transverse filaments of SYCP1 link axial/lateral elements to a central element containing SYCE1 and SYCE2, thus forming the synaptonemal complex (reviewed in Yang and Wang 2009). Unsynapsed regions are silenced during pachynema by recruitment of BRCA1 and ATR, which phosphorylates histone H2AX (reviewed in Inagaki et al. 2010).
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Inagaki A, Schoenmakers S, Baarends WM.; ''DNA double strand break repair, chromosome synapsis and transcriptional silencing in meiosis.''; PubMedEurope PMCScholia
Scully R, Chen J, Plug A, Xiao Y, Weaver D, Feunteun J, Ashley T, Livingston DM.; ''Association of BRCA1 with Rad51 in mitotic and meiotic cells.''; PubMedEurope PMCScholia
Ward IM, Chen J.; ''Histone H2AX is phosphorylated in an ATR-dependent manner in response to replicational stress.''; PubMedEurope PMCScholia
Tarsounas M, Pearlman RE, Gasser PJ, Park MS, Moens PB.; ''Protein-protein interactions in the synaptonemal complex.''; PubMedEurope PMCScholia
Scherthan H, Weich S, Schwegler H, Heyting C, Härle M, Cremer T.; ''Centromere and telomere movements during early meiotic prophase of mouse and man are associated with the onset of chromosome pairing.''; PubMedEurope PMCScholia
Roig I, Liebe B, Egozcue J, Cabero L, Garcia M, Scherthan H.; ''Female-specific features of recombinational double-stranded DNA repair in relation to synapsis and telomere dynamics in human oocytes.''; PubMedEurope PMCScholia
BRCA1 localizes to axial elements of the synaptonemal complex in unsynapsed regions of chromosomes. The localization requires SYCP1 of the synaptonemal complex.
Axial elements begin assembling as short linear segments along the long axis of the chromosome in leptotene phase. Eventually the short segments will fuse to form the complete axial element along the entire length of the chromosome. After synapsis the axial elements are also known as lateral elements of the synaptonemal complex. Within axial elements the sister chromatids are bound together by meiotic cohesin (Prieto et al. 2004, Garcia-Cruz et al. 2010). The bound chromatids are anchored to a complex containing SYCP2 and SYCP3 via a direct or indirect interaction with cohesin (Garcia-Cruz et al. 2010).
As sections of the axial elements form, the telomeres migrate to one site on the inner nuclear membrane to form the telomere bouquet (Scherthan et al. 1996). A current model shows the synaptonemal complex interacting with SUN1 and SUN2, which span the inner membrane and bind Nesprin-1 and Nesprin-2, which span the outer membrane and bind cytoplasmic actin. Lamin-B1 and Lamin-C2 are located adjacent to the attachment plate on the inner membrane.
Unsynapsed regions of chromosomes accumulate BRCA1, the kinase ATR, and the phosphorylated histone gammaH2AX. In mouse the recruitment of ATR depends on BRCA1.
Unsynapsed regions of chromosomes are silenced during pachytene phase by a process called Meiotic Silencing of Unsynapsed Chromatin (MSUC) and, in the case of the X and Y chromosomes, Meiotic Sex Chromosome Inactivation (MSCI). Unsynapsed meiotic chromatin recruits BRCA1 (Scully et al. 1997, Garcia-Cruz et al. 2009). In mouse, the recruitment requires SYCP3 of axial elements of the synaptonemal complex, which may remain exposed in unsynapsed regions.
Initiation of recombination precedes and is required for synapsis (Roig et al. 2004). The synaptonemal complex forms when transverse filaments of SYCP1 link axial/lateral elements of sister chromatids to a central element comprising SYCE1, SYCE2, and other proteins (Tarsounas et al. 1997). The order of assembly is unknown.
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Element of Synaptonemal
ComplexProcessed Telomere End and Associated DNA Binding and Packaging Protein Complex Folded Into Higher Order
StructureAnnotated Interactions
Element of Synaptonemal
ComplexElement of Synaptonemal
ComplexElement of Synaptonemal
ComplexProcessed Telomere End and Associated DNA Binding and Packaging Protein Complex Folded Into Higher Order
Structure