Synaptonemal complex: The structural basis for meiosis I.

As a specialized form of cell division for the generation of haploid gametes, meiosis is characterized by the separation of homologous chromosomes in meiosis I. Two key events take place in meiotic prophase I to ensure the proper segregation of homologous chromosomes, including the formation of the synaptonemal complex (SC) and the initiation and repair of programmed DNA double-strand breaks (DSBs). Both of these events are essential for the generation of crossovers. The SC serves as the structural basis of all the chromosome behaviors in meiotic prophase I. It not only reorganizes the chromosomes into a highly ordered stem-loop structure and holds the homologous chromosomes together when DSBs are being repaired, but also works as a platform for the recruitment of proteins playing essential roles in the formation and repair of DSBs, as well as the checkpoint monitoring the proper meiosis progression. Given the critical role of the SC in meiosis, questions concerning its structure and function are well studied in the field of meiosis research. Here, we not only reviewed the studies concerning the assembly of the SC, the function of the SC during male meiosis, and how mutations related to the SC coding genes affect male fertility, but also summarized the critical questions to be solved in future research.