Recombination, Pairing, and Synapsis of Homologs during Meiosis

Abstract

Recombination is a prominent feature of meiosis in which it plays an important role in increasing genetic diversity during inheritance. Additionally, in most organisms, recombination also plays mechanical roles in chromosomal processes, most notably to mediate pairing of homologous chromosomes during prophase and, ultimately, to ensure regular segregation of homologous chromosomes when they separate at the first meiotic division. Recombinational interactions are also subject to important spatial patterning at both early and late stages. Recombination-mediated processes occur in physical and functional linkage with meiotic axial chromosome structure, with interplay in both directions, before, during, and after formation and dissolution of the synaptonemal complex (SC), a highly conserved meiosis-specific structure that links homolog axes along their lengths. These diverse processes also are integrated with recombination-independent interactions between homologous chromosomes, nonhomology-based chromosome couplings/clusterings, and diverse types of chromosome movement. This review provides an overview of these diverse processes and their interrelationships.

The F-Box Protein ZYGO1 Mediates Bouquet Formation to Promote Homologous Pairing, Synapsis, and Recombination in Rice Meiosis

“…The restricted distribution of HEI10 foci implied that HEI10 might be able to promote CO formation on the partially synapsed chromosomes, but might lose its function in the unsynapsed region. As normal CO maturation depends on normal chromosome alignment (Lambing et al, 2015;Zickler and Kleckner, 2015), the defects in CO formation might be caused by the failure in full-length chromosome alignment in zygo1.…”

“…Accordingly, prophase I has been divided into five cytological substages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Zygotene is a complicated and dynamic stage, during which homologous recombination is ongoing, and pairing as well as synapsis initiate (Zickler and Kleckner, 2015). Meanwhile, a highly polarized nuclear reorganization occurs at this stage, involving an aggregation of chromosomes and/or the formation of a "bouquet" in which telomeres are spatially tethered to a limited area of the inner nuclear membrane (INM) (Zickler and Kleckner, 1998).…”

Evolutionary mysteries in meiosis

“…The synaptonemal complex then disappears, and homologues remain tethered at CO positions and centromeres. The precise function of the synaptonemal complex is not entirely understood [20]; one possibility is that it may serve to stabilize homologues during CO maturation. Some pairing mechanism must be advantageous to ensure proper segregation of homologues, but the origins and selective advantage of extensive pairing, synapsis, gene conversion and recombination remain poorly understood [24].…”

“…This homology search is mediated by the active formation of numerous DNA double-strand breaks (DSBs) followed by chiasmata formation, but less wellknown mechanisms of recombination-independent pairing also exist [20]. Non-homologous centromere coupling is also often observed at this stage, but the functional and evolutionary significance of this coupling is elusive [21].…”

DNA-Pairing and Annealing Processes in Homologous Recombination and Homology-Directed Repair

“…During meiosis, the formation of heteroduplex DNA facilitates crossing-over and allelic exchange between homologous chromosomes; this process ensures that progeny are not identical clones of their parents and that sexual reproduction between individuals will result in a genetically diverse population (see Lam and Keeney 2015;Zickler and Kleckner 2015). Heteroduplex DNA generated by meiotic COs also ensures proper segregation of homologous chromosomes, so that each gamete receives a complete but genetically distinct set of chromosomes (BascomSlack et al 1997;Gerton and Hawley 2005).…”