Progression of meiotic recombination requires structural maturation of the central element of the synaptonemal complex

The synaptonemal complex is an elaborate meiosis-specific supramolecular protein assembly that promotes chromosome synapsis and meiotic recombination. We inactivated the meiosis-specific gene Tex12 and found that TEX12 is essential for progression of meiosis in both male and female germ cells. Structural analysis of the synaptonemal complex in Tex12^-/- meiocytes revealed a disrupted central element structure, a dense structure residing between the synapsed homologous chromosomes. Chromosome synapsis is initiated at multiple positions along the paired homologous chromosomes in Tex12^-/- meiotic cells, but fails to propagate along the chromosomes. Furthermore, although meiotic recombination is initiated in Tex12^-/- meiotic cells, these early recombination events do not develop into meiotic crossovers. Hence, the mere initiation of synapsis is not sufficient to support meiotic crossing-over. Our results show that TEX12 is a component of the central element structure of the synaptonemal complex required for propagation of synapsis along the paired homologous chromosomes and maturation of early recombination events into crossovers.