SPD-2/CEP192 and CDK Are Limiting for Microtubule-Organizing Center Function at the Centrosome

Abstract

The centrosome acts as the microtubule-organizing center (MTOC) during mitosis in animal cells. Microtubules are nucleated and anchored by γ-tubulin ring complexes (γ-TuRCs) embedded within the centrosome's pericentriolar material (PCM). The PCM is required for the localization of γ-TuRCs, and both are steadily recruited to the centrosome, culminating in a peak in MTOC function in metaphase. In differentiated cells, the centrosome is often attenuated as an MTOC and MTOC function is reassigned to non-centrosomal sites such as the apical membrane in epithelial cells, the nuclear envelope in skeletal muscle, and down the lengths of axons and dendrites in neurons. Hyperactive MTOC function at the centrosome is associated with epithelial cancers and with invasive behavior in tumor cells. Little is known about the mechanisms that limit MTOC activation at the centrosome. Here, we find that MTOC function at the centrosome is completely inactivated during cell differentiation in C. elegans embryonic intestinal cells and MTOC function is reassigned to the apical membrane. In cells that divide after differentiation, the cellular MTOC state switches between the membrane and the centrosome. Using cell fusion experiments in live embryos, we find that the centrosome MTOC state is dominant and that the inactive MTOC state of the centrosome is malleable; fusion of a mitotic cell to a differentiated or interphase cell results in rapid reactivation of the centrosome MTOC. We show that conversion of MTOC state involves the conserved centrosome protein SPD-2/CEP192 and CDK activity from the mitotic cell.

Polo-like kinase phosphorylation determines Caenorhabditis elegans centrosome size and density by biasing SPD-5 toward an assembly-competent conformation

“…The role of PLK-1 in PCM assembly, then, is to bias SPD-5 isomerization towards the assembly-competent state. Besides PLK-1 phosphorylation, PCM assembly requires SPD-2, a protein known to control centrosome growth rate and thus size in vivo (Decker et al, 2011; Yang and Feldman, 2015). We have shown previously that SPD-2 accelerates SPD-5 assembly in the presence and absence of PLK-1 in vitro , demonstrating that multiple mechanisms regulate SPD-5 self-assembly (Woodruff et al, 2015).…”

Coordination of cellular differentiation, polarity, mitosis and meiosis – New findings from early vertebrate oogenesis

“…Then polarization is in effect executed during bouquet stages through the MVC (Elkouby et al, 2016). Such a dual and dynamic role of the centrosome in cell division and the immediately following polarization during differentiation was beautifully demonstrated in the developing C. elegans gut (Feldman & Priess, 2012; Yang & Feldman, 2015). In this system the apical-basal polarity of differentiating gut epithelial cells is aligned with their previous cell division plane.…”

Microtubule-organizing centers: from the centrosome to non-centrosomal sites

“…For example, γ–tubulin localizes to the cell cortex of C. elegans germ cells, at hemidesmosomes of C. elegans epidermal cells, surrounding nuclei of cultured muscle cells, at the Golgi membrane in RPE1 cells, and along the apical membrane of Drosophila tracheal cells, C. elegans intestinal cells, and Caco-2 and WIF-B epithelial cell lines [13,14,20,23,24,27,37,54]. Microtubules appear to regrow from these sites following induced depolymerization, suggesting that γ–TuRCs might control microtubule nucleation there.…”