The DNA mismatch-repair MLH3 protein interacts with MSH4 in meiotic cells, supporting a role for this MutL homolog in mammalian meiotic recombination.

The mismatch-repair (MMR) system plays a central role in maintaining genetic stability and requires evolutionarily conserved protein factors, including MutS and MutL homologs. Since the discovery of a link between the malfunction of post-replicative MMR and human cancers, a number of works have focused on the function of MutS and MutL homologs in the correction of replication errors. However, several MutS-like and MutL-like proteins also participate in meiotic recombination. The MutL homolog MLH3 has been recently identified in mammals. Several pieces of evidence support a role for this protein in post-replicative MMR. To investigate whether MLH3 also acts during meiotic recombination, we analyzed its expression in mammalian germ cells. The MLH3 gene is expressed in mouse meiotic cells and in human testis, and, as revealed by immunoprecipitation assays, the MLH3 protein is found in mouse spermatocytes. We further demonstrate that the meiosis-specific MSH4 protein, known to participate to meiotic recombination, is co-immunoprecipitated with MLH3 from mouse meiotic cell extracts. In addition, the two MLH3 protein isoforms potentially expressed in human testis (hMLH3 and hMLH3 Delta 7) interact in vitro with the hMSH4 protein. These interaction data suggest that MLH3 is associated with MSH4 in mammalian meiotic cells, and strongly support the possibility that MLH3 plays a role in mammalian meiotic recombination.