Meiosis is a specialized form of cell division that gives rise to haploid reproductive cells by replicating the genetic material once and undergoing two rounds of partitioning. While most forms of cell division require centrosomes to assemble a bipolar microtubule-based spindle that segregates chromosomes, female gametes (oocytes) are unique in that in most species their divisions occur in the absence of centrosomes. Instead, oocytes use alternative means to assemble bipolar spindles and facilitate chromosome segregation without these canonically essential structures. Understanding these mechanisms is of particular importance due to the error-prone nature of female meiosis and the dire consequences of aneuploidy in the oocyte. To this end, I have used the experimentally tractable nematode Caenorhabditis elegans as a model system. Unlike most cell types, homologous chromosome pairs (bivalents) in C. elegans oocytes congress and segregate in a kinetochore-independent manner. Instead of forming end-on kinetochore attachments, microtubules instead run along the sides of bivalents in laterally associated bundles. A ring-shaped protein complex (“ring complex;” RC) wraps around the mid-bivalent region in Meiosis I and the sister chromatid interface in Meiosis II. The RC is made up of dozens of known protein components that represent a diverse range of functional classes. The RC is essential for spindle assembly and chromosome congression and segregation in C. elegans oocytes; depletion of the RC causes gross defects that ultimately lead to meiotic failure. While the broad functions of the RC have been extensively characterized, gaps remain in our understanding of the specific contributions of individual protein components. Furthermore, how this essential structure interacts with nearby proteins on the kinetochore and chromosome arms has yet to be extensively investigated. In this dissertation, I describe my contributions to our understanding of how the RC and other bivalent-associated proteins collaborate to ensure faithful chromosome congression and segregation on acentrosomal spindles. My work provides insight into the relationship between bivalent morphology and RC structure by uncovering novel structural motifs within the RC that weave through the homologous chromosome interface in Meiosis I, and I show that biorientation of the bivalent such that the two lobes point toward opposite spindle poles is required for proper chromosome congression and segregation. Additionally, I describe how two chromosome-associated motors, KLP-19 and KLP-7, make unique contributions to spindle architecture through their regulation of microtubule dynamics in metaphase. Finally, I show preliminary work describing a collaborative role between the RC and outer kinetochore in retaining chromosomes within the spindle, suggesting that each of these protein complexes make distinct contributions to the physical positioning of bivalents. Taken together, this work expands our understanding of how the chromosome contributes to the mechanisms guiding acentrosomal cell division; by using multiple protein complexes to associate with and regulate microtubules, the bivalent guides the assembly of the macromolecular machine that ensures its faithful partitioning. Further investigation into chromosome-associated proteins is sure to yield additional valuable insights into the unique and important phenomenon of acentrosomal female meiosis.

Creator

• Horton, Hannah Elizabeth

DOI

• https://doi.org/10.21985/n2-6d4s-6631

Subject

• Cellular biology

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16528
• etdadmin_upload_984240

Date created

• 2023-01-01

Resource type

• Dissertation

Rights statement

• In Copyright