Drosophila Spd-2 Recruits PCM to the Sperm Centriole, but Is Dispensable for Centriole Duplication

In C. elegans, genome-wide screens have identified just five essential centriole-duplication factors: SPD-2, ZYG-1, SAS-5, SAS-6, and SAS-4 1-8. These proteins are widely believed to comprise a conserved core duplication module 3, 9-14. In worm embryos, SPD-2 is the most upstream component of this module, and it is also essential for pericentriolar material (PCM) recruitment to the centrioles 1, 4, 15, 16. Here, we show that Drosophila Spd-2 (DSpd-2) is a component of both the centrioles and the PCM and has a role in recruiting PCM to the centrioles. DSpd-2 appears not, however, to be essential for centriole duplication in somatic cells. Moreover, PCM recruitment in DSpd-2 mutant somatic cells is only partially compromised, and mitosis appears unperturbed. In contrast, DSpd-2 is essential for proper PCM recruitment to the fertilizing sperm centriole, and hence for microtubule nucleation and pronuclear fusion. DSpd-2 therefore appears to have a particularly important role in recruiting PCM to the sperm centriole. We speculate that the SPD-2 family of proteins might only be absolutely essential for the recruitment of centriole duplication factors and PCM to the centriole(s) that enter the egg with the fertilizing sperm.