Spd-2 Gene Duplication Suggests Cell-Type Specific Assembly Mechanisms of Pericentriolar Material

Centrosomes are multi-protein complexes that function as the major microtubule organizing center (MTOC) for the cell. While centrosomes play tissue-specific MTOC functions, little is known about how particular centrosome proteins are regulated across cell types to achieve these different functions. To investigate this cell type-specific diversity, we searched for gene duplications of centrosome genes in the Drosophila lineage with the aim of identifying centrosome gene duplications where each copy evolved for specialized functions. Through in depth functional analysis of a Spd-2 gene duplication in the Willistoni group, we discovered differences in the regulation of PCM in somatic and male germline cells. The parental gene, Spd-2A , is expressed in somatic cells, where it can function to organize pericentriolar material (PCM) and the mitotic spindle in larval brain neuroblasts. Spd-2A is absent during male meiosis, and even when ectopically expressed in spermatocytes it fails to rescue PCM and spindle organization. In contrast, the new gene duplicate, Spd-2B , is expressed specifically in spermatocytes. During male meiosis, Spd-2B localizes to centrosomes, organizes PCM and spindles, and is sufficient for proper male fertility. Experiments using chimeric transgenes reveal that differences in the C-terminal tails of Spd-2A and Spd-2B are responsible for these functional changes. Thus, Spd-2A and Spd-2B have evolved complementary functions by specializing for distinct subsets of cells. Together, our results demonstrate that somatic cells and male germline cells have fundamentally different requirements for PCM, suggesting that PCM proteins such as Spd-2 is differentially regulated across cell types to satisfy distinct requirements. Highlights Spd-2 gene duplication in the Willistoni group is rapidly evolving Parent gene Spd-2A is expressed in somatic cells, whereas the gene duplicate Spd-2B is expressed in spermatocytes Spd-2A organizes pericentriolar material during somatic cell mitosis Spd-2B is specialized for pericentriolar material organization during male meiosis