The mammalian SPD-2 ortholog Cep192 regulates centrosome biogenesis

Centrosomes are the major microtubule-organizing centers of mammalian cells. They are composed of a centriole pair and surrounding microtubule-nucleating material termed pericentriolar material (PCM) [1]. Bipolar mitotic spindle assembly relies on two intertwined processes: centriole duplication and centrosome maturation. In the first process, the single interphase centrosome duplicates in a tightly regulated manner so that two centrosomes are present in mitosis [2, 3]. In the second process, the two centrosomes increase in size and microtubule nucleation capacity through PCM recruitment, a process referred to as centrosome maturation [4]. Failure to properly orchestrate centrosome duplication and maturation is inevitably linked to spindle defects, which can result in aneuploidy and promote cancer progression [5]. It has been proposed that centriole assembly during duplication relies on both PCM and centriole proteins, raising the possibility that centriole duplication depends on PCM recruitment [6]. In support of this model, C. elegans SPD-2 and mammalian NEDD-1 (GCP-WD) are key regulators of both these processes [7 - 13]. SPD-2 protein sequence homologs have been identified in flies, mice, and humans, but their roles in centrosome biogenesis until now have remained unclear [10, 14 - 16]. Here, we show that Cep192, the human homolog of C. elegans and D. melanogaster SPD-2, is a major regulator of PCM recruitment, centrosome maturation, and centriole duplication in mammalian cells. We propose a model in which Cep192 and Pericentrin are mutually dependent for their localization to mitotic centrosomes during centrosome maturation. Both proteins are then required for NEDD-1 recruitment and the subsequent assembly of gamma-TuRCs and other factors into fully functional centrosomes.