Synapsis – the pairing of homologous chromosomes during prophase in meiosis I – is mediated by a large zipper-like protein complex called the synaptonemal complex. The incorrect assembly of the synaptonemal complex causes impaired meiotic recombination and cell death, which leads to infertility in males and aneuploidy in females, but the details of how the complex forms in mammals remain obscure. On , Geert Hamer and colleagues explore the function of testis-expressed protein 12 (TEX12), which they previously identified as a component of the central element of the synaptonemal complex. The authors now show that, in Tex12–/– mice, meiotic progression is impaired in both male and female germ cells, which leads to infertility. They go on to show that the structure of the central element is disrupted in Tex12–/– meiocytes. Moreover, although synapsis is initiated at multiple positions along the paired homologous chromosomes, it fails to propagate along the chromosomes. Importantly, meiotic recombination is impaired in the mutant cells – double-strand breaks occur, but these do not develop into meiotic crossovers. The authors conclude that the initiation of synapsis is not sufficient for meiotic recombination.
