Germline-specific role for unconventional components of the γ-tubulin complex in Caenorhabditis elegans.

The γ-tubulin complex (γTuC) is a widely conserved microtubule nucleator, but some of its components GCP4-6 have not been detected in Caenorhabditis elegans. Here, we identified two γTuC-associated proteins in C. elegans, namely GTAP-1 and -2, for which apparent orthologs were detected only in the genus Caenorhabditis. They were localized at centrosomes and the plasma membrane of the germline, and their centrosomal localization was interdependent. In early C. elegans embryos, whereas the conserved γTuC component MZT-1/MOZART1 was essential for the localization of centrosomal γ-tubulin, depletion of GTAP-1 and/or -2 caused up to 50% reduction of centrosomal γ-tubulin and precocious disassembly of spindle poles during mitotic telophase. In the adult germline, GTAP-1 and GTP-2 contributed to the efficient recruitment of γTuC to the plasma membrane. Depletion of GTAP-1, but not GTAP-2, severely disrupted both the microtubule array and the honeycomb-like structure in the adult germline. We propose that GTAP-1 and -2 are unconventional components of γTuC that contribute to the organization of both centrosomal and non-centrosomal microtubules by targeting the γTuC to specific subcellular sites in a tissue-specific manner.