Meiotic Transverse Filament Proteins: Essential for Crossing Over

Meiosis is a specialized set of two nuclear divisions, meiosis I and II, by which a diploid cell produces four haploid daughters. After premeiotic DNA replication, homologous chromosomes pair and recombine, and then disjoin at meiosis I. Subsequently, at meiosis II, the sister chromatids of each chromosome segregate. In nearly all eukaryotes, meiotic chromosome pairing culminates in the formation of a ladderlike supramolecular protein structure, the synaptonemal complex (SC) (Page and Hawley, 2004). The rungs of the ladder are known as transverse filaments (TFs). Genes encoding TF proteins have been identified in a limited number of organisms, and their function has been studied by mutational analysis. Although TF proteins show little amino acid sequence conservation, their structure and function are largely conserved. In all analyzed species, TF proteins are required for meiotic reciprocal recombination (crossing over).