DEPLETION OF NUCLEAR ENVELOPE COMPONENTS CAUSES A NOVEL CENTROSOME ATTACHMENT DEFECT
Open Access
- Author:
- Gao, Zhizhen
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 10, 2008
- Committee Members:
- Wendy Hanna Rose, Thesis Advisor/Co-Advisor
Christian Lorenzo Malone, Thesis Advisor/Co-Advisor - Keywords:
- Lamin-binding proteins
Nuclear lamins
Nuclear size
Centrosome attachment
Nuclear Pores - Abstract:
- The attachment of the centrosome to the nucleus is essential for C. elegans development. Two genes, zyg-12 and sun-1, are essential for centrosome attachment; zyg-12 mutant and sun-1(RNAi) (also called mtf-1) embryos are defective in the attachment of both centrosomes in 100% of 1-cell embryos. Here we report that several lamin network proteins and nuclear import components are involved in centrosomal attachment. Disruption of C. elegans lamin frequently resulted in a single detached centrosome, while the second centrosome remained associated with the nucleus. Disrupting lamin-binding proteins by RNAi co-depletion of emr-1 (emerin) and lem-2 (MAN-1) or by RNAi of baf-1 (BAF) resulted in an identical single detached centrosome phenotype. In addition, the same phenotype was observed in C. elegans nucleoporin NPP-6 or importin-depleted embryos as well. The localization of ZYG-12 and SUN-1 to the nuclear envelope was normal in all of these RNAi-treated embryos. We conclude that the reason for centrosomal detachment in lamina network proteins RNAi embryos may be different from that of ZYG-12- or SUN-1- depleted embryos. All of the RNAi-treated embryos also show reduced nuclear size. We proposed that reduced nuclear size causes the single detached centrosome. We observed these RNAi embryos and wild-type as nuclear size increased during the cell cycle, a common event in pronuclear migration. As the cell cycle progresses, the detached centrosome was observed to frequently migrate to the sperm pronucleus and attach. This attachment occurred as the nuclei reached a reproducible size, suggesting a threshold of available nuclear surface area that is required for attachment. In embryos fertilized with anucleated sperm, the normal size female pronucleus can hold two even three centrosomes. However, the small female pronucleus can only capture one centrosome and the other one only moved slightly toward the nucleus. We conclude that the attachment of centrosome to the nucleus depends on the interaction between the nuclear surface area and the microtubules.