Polar body emission (PBE), a form of asymmetric division, occurs twice during vertebrate oocyte maturation and is required to produce a haploid egg for sexual reproduction. Our lab elucidated parts of the mechanism that regulates PBE in Xenopus laevis oocytes. Cdc42 and RhoA, two GTPases, were shown to mediate membrane protrusion and the contractile ring, respectively. It is believed that cdc42 is mediating the protrusion by regulating actin polymerization. However, it is not clear what upstream signaling pathway regulates cdc42 activation during PBE. One possibility is calcium signaling, which occurs at fertilization, and is required for second PBE. Interestingly, the fertilization calcium transient also regulates cortical granule exocytosis/membrane retrieval, a process that also involves cdc42-mediated actin assembly. Furthermore, active cdc42 and RhoA are found in non-overlapping concentric zones in single-cell wound healing; their activation requires calcium signaling. To determine possible calcium transients during polar body emission, we employed the calcium-binding C2 domain of PKCβ in live cell imaging. Surprisingly, the most prominent C2 signal was seen after cdc42 activation and membrane protrusion. Co-localization experiments indicated that the C2 signal appeared at the cortical area marked by the contractile ring component anillin, and after partial constriction of the ring. Injection of the calcium chelator, dibromo-BAPTA, abolished the C2 signal, suggesting that it is indeed depicting a calcium transient. Dibromo-BAPTA injection also inhibited polar body abscission, as assessed by a novel abscission assay developed in our lab. We have for the first time detected a calcium signal during PBE that is essential to the last step of cytokinesis—abscission.

The molecular mechanics of bacterial cell division remain one of the most fundamental unsolved problems in bacterial cell biology. During bacterial cytokinesis, bacteria divide symmetrically to give rise to two identical daughter cells. This tightly regulated process is orchestrated by an assembly of essential cell division proteins that form a supramolecular structure known as the divisome. The divisome, which forms at the cell centre, is responsible for the invagination and fusion of the cell’s membrane and peptidoglycan layers. The Escherichia coli divisome is comprised of at least ten essential proteins whose individual functions are mostly unknown. These divisomal proteins are recruited in a semi-hierarchical order, with the early recruits being predominantly cytoplasmic and the later recruits being predominantly extracytoplasmic or multi-pass transmembrane proteins. DivIB and its ortholog FtsQ are essential members of the divisome in Gram-positive and Gram-negative bacteria, respectively. DivIB is a bitopic membrane protein composed of an N-terminal cytoplasmic domain, a single-pass transmembrane domain, and a C-terminal extracytoplasmic region comprised of three separate protein domains. The α domain is located next to the transmembrane segment and is a polypeptide-transport-associated (POTRA) domain. The β domain comprises approximately half of the extracytoplasmic region, and has a unique three-dimensional fold. The most C-terminal domain, the γ domain, is relatively unstructured. This protein has been proposed to play a role in septal peptidoglycan cross-linking or lengthening. The primary aims of these studies were to further characterise the structure and function of the bacterial cell division protein DivIB as well as investigate the interactions this protein has with the other divisomal proteins. It was anticipated that the knowledge gained should aid in the development of antimicrobials that target this protein’s function or protein-protein interactions. A molecular dissection approach was used to determine which of DivIB’s domains are essential for its recruitment to incipient division sites and for its cell division functions. It was determined that DivIB has three molecular epitopes that mediate its localisation to division septa; two epitopes are encoded within the extracytoplasmic region while the third is located in the transmembrane domain. It is proposed that these epitopes represent sites of interaction with other divisomal proteins, and this information was used to develop a model of the way in which DivIB and FtsQ are integrated into the divisome. Remarkably, two of the three DivIB localisation epitopes are dispensable for vegetative cell division; this suggests that the divisome is assembled using a complex network of protein-protein interactions, many of which are redundant and likely to be individually nonessential. Yeast and bacterial two-hybrid studies have revealed that most of these proteins have multiple binding partners, making it difficult to pinpoint epitopes that mediate the interaction between pairs of interacting proteins. Recently, a heterologous septal targeting approach was introduced to study the interaction between Bacillus subtilis divisomal proteins in E. coli. This technique allows the interaction between pairs of divisomal proteins to be studied in vivo without the complications caused by other interacting proteins. This approach was used to perform a molecular dissection of the interaction between B. subtilis DivIB and the divisomal transpeptidase PBP 2B. Although both proteins have septal localisation determinants in their transmembrane domains, it was found that these regions do not mediate their interaction. Rather, it was shown that DivIB interacts with PBP 2B through its extracytoplasmic region. Dissection studies revealed that all three extracytoplasmic domains of DivIB are necessary for interaction with PBP 2B, suggesting that the two proteins make multiple interactions, each of which is not strong enough in isolation to mediate formation of a stable complex. Finally, it was shown that E. coli FtsQ localises to the division septum in B. subtilis but cannot complement a divIB null. Multi-angle laser light scattering (MALLS) analysis revealed that the extracytoplasmic domain of Geobacillus stearothermophilus DivIB is predominantly monomeric at high concentrations. This indicated that if DivIB does exist as a dimer in vivo, it dimerises through its cytoplasmic or transmembrane region. In vitro observations suggest the C-terminal residues of DivIB may play a role in peptidoglycan binding. Finally, attempts were made to determine the three-dimensional structure of the complete extracytoplasmic domain of DivIB. Although it proved impossible to determine the structure using NMR spectroscopy, crystals were obtained under many different crystallisation conditions. Despite diffracting to 3.5 Å, we were unable to solve the protein structure using X-ray crystallography. However, this work has laid the groundwork for future attempts at solving the structure of this protein using X-ray crystallography.

Errata is pasted onto back end paper. / Includes bibliographical references (26 leaves). / 115, [68] leaves, [8] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study entailed work towards the isolation of the pbl gene and preliminary characterisation of a candidate pbl transcript. Plasmid rescue of the genomic DNA flanking the inserted P element led to the isolation of a third candidate p61 cDNA, the 1A cDNA. This data suggests that the IA cDNA is encoded by the p61 gene. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1998

Errata is pasted onto back end paper. / Includes bibliographical references (26 leaves). / 115, [68] leaves, [8] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study entailed work towards the isolation of the pbl gene and preliminary characterisation of a candidate pbl transcript. Plasmid rescue of the genomic DNA flanking the inserted P element led to the isolation of a third candidate p61 cDNA, the 1A cDNA. This data suggests that the IA cDNA is encoded by the p61 gene. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1998

In the budding yeast Saccharomyces cerevisiae, endocytosis comprises bulk uptake (fluids and membranes) and receptor-mediated internalisation (membrane proteins). Both processes require efficient actin filament assembly. Key factors that nucleate the assembly of actin filaments are the Arp2/3 complex and a number of NPFs (Nucleation Promoting Factors), which are responsible for temporal and spatial regulation of Arp2/3 activity. In yeast, in addition to Las17p, the orthologue of WASP (Wiskott-Aldrich syndrome protein), one type I unconventional myosin (Myo5p) exhibits strong NPF activity through coordination with the WH2 (WASP Homology 2) domain containing protein Vrp1p, the yeast orthologue of WIP (WASP Interacting Protein). Here, we identified another key Vrp1p domain (Hof One Trap/HOT), which binds directly to the SH3 domain of the cytokinesis protein Hof1p, is important for Vrp1p function in vivo. The key function of the Vrp1p HOT domain is to counteract the inhibitory effect of the Hof1p SH3 domain in Myo5p-stimulated actin assembly and endocytosis. We have also revealed a novel actin monomer binding domain (VH2) in Vrp1p, which is functionally redundant with the WH2 domain. Receptormediated endocytosis requires stable interaction of Vrp1p with Las17p. However, we find that bulk uptake of fluid and membrane takes place without Vrp1p-Las17p association and requires only functional WH2 and HOT domains of Vrp1p. Finally, we identified a number of other potential Hof1p SH3 domain interactors using an affinity isolation approach and compared this interaction profile with those of several other yeast SH3 domains. The unique Vrp1p-Hof1p interaction pattern allows us to gain insight into the pathology of Wiskott-Aldrich syndrome.

Thesis (Ph.D) -- McMaster University, 1997 / Includes bibliographical references Also available via World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Robert M. Dyer, Dept. of Animal and Food Sciences. Includes bibliographical references.

Thesis (M.D.)--University of Copenhagen. / Summary in Danish. Bibliography: p. 47-59.

Thesis (M.S.)--The University of North Carolina at Greensboro, 2009. / Directed by Paul Steimle; submitted to the Dept. of Biology. Title from PDF t.p. (viewed May 11, 2010). Includes bibliographical references (p. 37-39).

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request