Files
Abstract
Protein degradation through cullin-RING ubiquitin ligases (CRLs) is required for theregulation of various cellular processes. Here we describe the regulation of mitotic progression, and nucleoli morphology and function by Cullin2 RING finger ubiquitin ligase (CRL2), and Cullin4 RING finger ubiquitin ligase (CRL4), respectively.Mitotic progression is mainly regulated by the activity of the mitotic cyclin, cyclin B1, and the cyclin dependent kinase, CDK1. The anaphase-promoting complex (APC/C) is known to target cyclin B1 for degradation, which is essential for mitotic exit. We discovered that the ubiquitin ligase CRL2ZYG11, with ZYG11 as the substrate receptor, also targets cyclin B1 for degradation independently of APC/C in Caernorhabditis elegans and humans. In C. elegans, we found that the CRL2ZYG11 mediated degradation of cyclin B1 is essential for meiotic progression. In mammalian cells, we found that CRL2ZYG11 is required for cyclin B1 degradation when the spindle assembly checkpoint (SAC) is active, which inactivates APC/C. This CRL2ZYG11 dependent cyclin B1 degradation in the absence of APC/C activity leads to mitotic slippage, a phenomenon where cells exit mitosis without dividing to become tetraploid. The nucleolus is the site of ribosome biogenesis in the cell. The morphology of the nucleolus is closely related to its function. Inactivation of the ubiquitin ligase CRL4 by mutating its adaptor protein ddb-1 results in a germ cell nucleoli morphology defect where the nucleoli are multi-lobed and irregularly shaped. We found that the substrate receptor DCAF-1 is responsible for the CRL4 mediated germ cell nucleoli defect. We also found that the morphology defect in the dcaf-1 germ cells correlated with a decrease in ribosome numbers, proving that ribosome biogenesis is affected. We discovered that this nucleoli defect is rescued by inactivating the sperm-fate specification protein FOG-1, and show that FOG-1 localization and levels are altered when dcaf-1 is depleted. Dafachronic acid (DA) is a steroid hormone that regulates dauer formation and life span in C. elegans. We found that DA negatively regulates adult germ cell proliferation in vitro and in vivo. We also discovered that regulation of germ cell proliferation by DA is adult-specific and does not affect larval germ cells.