During meiosis, homologous chromosomes pair, synapse, and undergo recombination to produce haploid gametes. In diverse species, telomere-led rapid movements of chromosomes promote homologous chromosome pairing during early meiotic prophase. These movements are generated by the tethering of telomeres to "LINC" (Linker of Nucleoskeleton and Cytoskeleton) complexes in the nuclear envelope (NE), which transmit cytoskeletal forces across the NE. In C. elegans, specialized chromosome regions known as Pairing Centers (PCs) recruit meiosis-specific zinc finger proteins, HIM-8, ZIM-1, ZIM-2, and ZIM-3, and associate with a LINC complex to generate chromosome movements instead of telomere-led movements. Loss of the zinc finger proteins abrogates the connection between PCs and LINC complex and leads to failures in homologous chromosome pairing, while mutations in an inner NE component of LINC complex, SUN-1, result in unregulated synapsis between non-homologous chromosomes. However, we do not yet understand the architecture of the connections between the zinc finger proteins and the NE, or how these connections regulate synapsis. Through a genetic screen for meiotic defects, we identified an uncharacterized gene that encodes a small, poorly conserved protein with a single transmembrane domain. We find that the protein localizes to the NE specifically during meiosis and is strongly enriched at the "patches" where the PCs interact with the LINC complex. We have named the protein MJL-1 (Majin-Like-1), based on its similarity to Majin, an inner NE protein that bridges the interaction between telomeres and LINC complex during meiosis in most metazoans. Mutations in MJL-1 abrogate the connection of PCs and LINC complex, and result in unregulated non-homolog synapsis, similar to mutations in sun-1. MJL-1 is thus essential for the tethering of PCs to LINC complex and rapid chromosome movements during meiotic prophase that regulate synapsis. Further investigation of MJL-1 will help to reveal how synapsis is regulated to ensure faithful recombination and segregation of homologous chromosomes during meiosis.

Affiliations:
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
- Howard Hughes Medical Institute, Chevy Chase, United States