Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Heidi Hehnly


Cenexin, Centrioles, Centrosome, Cilia, Kupffer's Vesicle (KV), Pericentriolar matrix (PCM)


The centrosome is a versatile cellular organelle that plays important roles in cell division and ciliogenesis. These functions are achieved through the different substructures of the centrosome including the centrioles, centriole appendages, and the pericentriolar matrix (PCM). Even though the various roles of the centrosome substructures in ciliogenesis and spindle formation have been extensively studied in vitro and in vivo using invertebrate models, our knowledge about whether these roles are maintained or diverge during vertebrate embryonic development remain lacking. Here, we use zebrafish and human cells as vertebrate models (chapters 2, 3, and 4) in comparison to C. elegans (chapter 2) to bridge the gap in our knowledge of the various roles played by the centrosome’s substructures during vertebrate embryonic development. This allowed us to determine what is conserved and what diverges from what is already known from in vitro studies and in other species. We first demonstrate that there is a conserved asymmetry in mitotic centrosome size across a mitotic spindle in both zebrafish and C. elegans embryos, however zebrafish centrosomes are disproportionately larger than those of C. elegans. What is unique about the asymmetry in zebrafish mitotic centrosomes is that the larger mitotic centrosome within a spindle is placed toward the center of the embryo in a manner that is dependent on the essential mitotic kinases Polo Like Kinase (PLK) 1 and PLK4. Second, we found that the C-terminus of Cenexin, a subdistal appendage protein, is required for the maintenance of PCM cohesion in a PLK1-dependent manner. Through phylogenetic analysis we identified that Cenexin’s C-terminus plays a conserved role in eukaryotes except for nematodes and arthropods. Lastly, we demonstrate that cilia formation in the Kupffer’s vesicle (KV) relies on the GTPases Rab35 and Rab11 and only require Rab8 for cilia elongation and extension into the lumen, which was different from in vitro cell culture studies that demonstrated a reliance on Rab8 for cilia and lumen formation. In the KV, cilia formation must be coordinated with lumen formation where cilia cannot extend into the extracellular space unless the growing lumen reaches a set area of 300μm2. This process relies on the same Rab35 and Rab11 GTPases to deliver the apical membrane protein CFTR required for lumenogenesis. Taken together, these studies highlight conserved and divergent roles of the centrosome substructures and signaling pathways at the centrosome, demonstrating the need for more comparative studies to understand the role of the centrosome’s substructures in various cellular processes.


Open Access

Available for download on Thursday, June 12, 2025