The Mammalian SPD-2 Ortholog Cep192 Regulates Centrosome Biogenesis

Abstract

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). 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. In the second process, the two centrosomes increase in size and microtubule nucleation capacity through PCM recruitment, a process referred to as centrosome maturation. Failure to properly orchestrate centrosome duplication and maturation is inevitably linked to spindle defects, which can result in aneuploidy and promote cancer progression. 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. In support of this model, C. elegans SPD-2 and mammalian NEDD-1 (GCP-WD) are key regulators of both these processes. SPD-2 protein sequence homologs have been identified in flies, mice, and humans, but their roles in centrosome biogenesis until now have remained unclear. 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.

Centrosomal protein of 192 kDa (Cep192) promotes centrosome-driven spindle assembly by engaging in organelle-specific Aurora A activation

“…Indeed, we found Cep192/oligomerization-mediated AurA activation to be critical for the function of MTOCs, both natural (centrosomes) and artificial (αAurA-coated beads). Parenthetically, the AurA-Cep192 function, reported here, is independent of centriole duplication/assembly (3,5,6), because exogenous, sperm nuclei-derived centrioles did not duplicate under the experimental conditions used (metaphase-arrested extract) (1, 2) and remained intact through the experiment (Fig. 3 A and D).…”

“…These observations suggest that the function of αAurA beads as MTOCs is a product of αAurA/dimerization-mediated AurA activation occurring on the bead surface. (3)(4)(5)(6), suggested that a common, Cep192-driven process underlies the development of MTOC activity by both centrosomes and αAurA beads. To explore this notion, we isolated a Xenopus laevis Cep192 cDNA encoding a 2,638 amino acid (aa), 289-kDa protein and raised Cep192-specific N-and C-terminally directed antibodies (αCep192-N and αCep192-C, respectively) ( Fig.…”

“…Protein recruitment during both centrosome duplication and maturation is controlled by centrosomal protein of 192 kDa (Cep192)/spindle defective 2 (Spd-2), a protein that operates by an unknown mechanism (3)(4)(5)(6). Among the proteins that localize to centrosomes in a Cep192-dependent manner is aurora A (AurA) (4,6), a serine/threonine kinase involved in mitotic entry, centrosome maturation, bipolar spindle assembly, and cell polarity (7,8).…”

Exploring the evolutionary history of centrosomes

“…SPD-2/ Cep192 proteins are recruited in the immediate vicinity of the centrioles and play a key role in organizing the PCM by recruiting CNN/CDK5RAP2 and microtubule-nucleating complexes [3,4,119]. Caenorhabidtis elegans and human SPD-2 homologues are also required for centriole duplication, but possibly indirectly through their ability to recruit PCM, as Drosophila SPD-2 is dispensable for centriole duplication [119][120][121]. Remarkably, an SPD-2 orthologue is encoded in the Dictyostelium genome and localizes to the corona that surrounds the NAB, which is functionally equivalent to the PCM [40].…”

“…Another possibility is that SPD-2 originally evolved to organize the poles of the mitotic spindle in Amorphea. In animals, SPD-2 family members are key to centrosome maturation, which leads to an increase in the microtubule-nucleation capacity of mitotic centrosomes required for centrosome-driven spindle assembly [121,123,124]. In chytrids and choanoflagellates, mitotic microtubules are nucleated in the immediate vicinity of the centrioles, which could involve SPD-2-dependent recruitment of microtubule-nucleating complexes.…”