LC2, the Chlamydomonas homologue of the t complex-encoded protein Tctex2, is essential for outer dynein arm assembly

Tctex2 is thought to be one of the distorter genes of the mouse t haplotype . This complex greatly biases the segregation of the chromosome that carrie s it such that in heterozygous +/t males, the t haplotype is transmitted to >95% of the offspring, a phenomenon known as transmission ratio distortion . The LC2 outer dynein arm light chain of Chlamydomonas reinhardtii is a ho mologue of the mouse protein Tctex2. We have identified Chlamydomonas inser tional mutants with deletions in the gene encoding LC2 and demonstrate that the LC2 gene is the same as the ODA12 gene, the product of which had not b een identified previously. Complete deletion of the LC2/ODA12 gene causes l oss of all outer arms and a slow jerky swimming phenotype. Transformation o f the deletion mutant with the cloned LC2/ODA12 gene restores the outer arm s and rescues the motility phenotype. Therefore, LC2 is required for outer arm assembly. The fact that LC2 is an essential subunit of flagellar outer dynein arms allows us to propose a detailed mechanism whereby transmission ratio distortion is explained by the differential binding of mutant (t hapl otype encoded) and wild-type dyneins to the axonemal microtubules of t-bear ing or wildtype sperm, with resulting differences in their motility.