The Genetics of Organelle Biogenesis Section studies the biogenesis and function of centrosomes, non-membrane-bound organelles that organize the microtubule cytoskeleton into large macromolecular machines such as the mitotic spindle and cilia.
We seek to understand the molecular mechanisms that govern the number and size of centrosomes. These non-membranes bound organelles play a central role in cell growth, division, signaling, and motility and are present at one to two copies per cell. Although defects in centrosome structure and number can have catastrophic effects on cell division and genome integrity, much remains to be learned about how the number and assembly of centrosomes is controlled.
Our current research focusing on identifying and characterizing genes required for assembly of the two components of the centrosome; the centrioles and the pericentriolar material. Our long-term goal is to define in molecular term, the regulatory networks that govern the number and size of centrosomes.
Our lab wants to understand how cells control centrosome number and size as these parameters are critically important for proper cell growth, and division. To address these questions, we use the small nematode worm C. elegans as a simple animal model system. Most worm genes have human counterparts and thus our identification of genes that control centrosome number and size in the worm can inform us about analogous processes that operate in humans. During the last decade, it has become increasingly apparent that defects in centrosome number and size are associated with a variety of human diseases and thus a more complete understanding of how the centrosome is regulated will allow us to better understand how diseases arise as a result of centrosome dysfunction.
Video of Centrosome amplification in a C. elegans embryo
This video was recorded by Jyoti Iyer, a research fellow in the laboratory of Dr. Kevin O’Connell and shows the first few cell cycles of a C. elegans embryo that lacks the protein phosphatase regulator SDS-22. The embryo expresses GFP::SPD-2, which marks centrosomes in green and mCherry::Histone, which marks chromatin in red. Centrosomes initially duplicate properly yielding 2 centrosomes per cell through the two cell stage. Centrosomes eventually over-duplicate giving rise to more than two centrosomes per cell at the four cell stage. From Peel N., Iyer J., Naik A., Dougherty M. P., Decker M., O'Connell K. F., 2017 Protein Phosphatase 1 Down Regulates ZYG-1 Levels to Limit Centriole Duplication. PLoS Genet. 13: e1006543.
Video of Centrosome duplication in a C. elegans embryo
This video was recorded by Nina Peel, a postdoctoral fellow in the laboratory of Dr. Kevin O’Connell and shows the first few cell cycles of a wild-type C. elegans embryo. The embryo expresses GFP::SPD-2, which marks centrosomes in green and mCherry::Histone, which marks chromatin in red. Notice that at the end of the first cell cycle, each centrosome duplicates precisely and resolves into two daughter centrosomes. These daughter centrosomes migrate around the DNA to direct chromosome segregation during the next cell cycle.
Video of Spindle assembly in a C. elegans embryo
This time-lapse recording of a wild-type C. elegans embryo expressing GFP::Tubulin was produced in the laboratory of Kevin O’Connell. The video begins with the maternal and paternal pronuclei uniting at the posterior of the embryo. Two microtubule asters formed by centrosomes associated with the paternal pronucleus grow in size and set up the first mitotic spindle. At the end of the first cell cycle, the spindle disassembles as each centrosome duplicates giving rise to another round of bipolar spindle formation at the two-cell stage.
Centrosome amplification in a C. elegans embryo
A four-cell C. elegans sds-22 mutant embryo with extra centrosomes. This is from our paper: Peel N., Iyer J., Naik A., Dougherty M. P., Decker M., O'Connell K. F., 2017 Protein Phosphatase 1 Down Regulates ZYG-1 Levels to Limit Centriole Duplication. PLoS Genet. 13: e1006543.
Electron micrograph of a C. elegans mother centriole
An electron micrograph of a C. elegans embryonic centriole. From: O'Connell K. F., Caron C., Kopish K. R., Hurd D. D., Kemphues K. J., Li Y., White J. G., 2001 The C. elegans zyg-1 gene encodes a regulator of centrosome duplication with distinct maternal and paternal roles in the embryo. Cell 105: 547–558.
Bipolar and monopolar spindle assembly in wild-type and mutant C. elegans embryos
Images of one- and two-cell C. elegans embryos stained for microtubules (red) and DNA (blue). Embryos on left are wild type and possess bipolar spindles. Embryos on right lack the kinase ZYG-1 and have monopolar spindles.
Microtubule organization in early C. elegans embryos
C. elegans embryos stained for microtubules (green), SPD-2 (red/yellow) and DNA (blue). From: Kemp C. A., Kopish K. R., Zipperlen P., Ahringer J., O'Connell K. F., 2004 Centrosome maturation and duplication in C. elegans require the coiled-coil protein SPD-2. Dev. Cell 6: 511–523.