Cell Cycle Regulation of the Centriolar Protein Ana2

Abstract

The centrosome functions to nucleate microtubule growth and organize the mitotic spindle during cell division. The centrosome normally duplicates once per cell cycle, ensuring a bipolar spindle that divides sister chromatids equally between two daughter cells during mitosis. However, improper duplication or over-duplication of centrosomes can lead to chromosomal instability, a hallmark of cancer. Two barrel-shaped structures called centrioles function as the duplication factors for centrosomes. Mutations in important centriole structural proteins can cause either down-regulation or amplification of centriole duplication. One of these proteins, Ana2, is required for duplication and mutations in its human orthologue, STIL, can cause disorders in neurological development. Normally, Ana2 localizes to an existing ‘mother' centriole during S-phase and plays an essential role in the assembly of the procentriole that will become a mature ‘daughter' during G2. In this study, we identified changes in total cellular levels of Ana2 by arresting S2 Drosophila cells in different phases of the cell cycle and immunoblotting for Ana2. We found that levels of both endogenous Ana2 and transiently overexpressed Ana2 are low during G1 and increase during S-phase. Endogenous Ana2 levels were highest in G2, consistent with centriole maturation during this phase of the cell cycle.