During development, Dictyostelium discoideum cells assume muticellularity via their collective aggregation. Cell-cell adhesion is required for morphogenesis, cell differentiation, cell sorting and gene expression during development. TgrC1 is a heterophilic cell adhesion molecule which is indispendable for complete development. TgrC1 can be considered as the most important cell adhesion molecule for D. discoideum development because deletion of the tgrC1 gene completely arrests development at the loose aggregate stage and inhibits fruiting body formation.
In order to investigate the biological role of TgrC1 during development, I have chosen to identify and charactize the extracellular heterophilic partner and the cytoplasmic binding partner(s) of TgrC1. Using different biochemical approaches, we identified TgrB1 as the heterophilic binding partner of TgrC1 and demonstrated that their association is mediated through IPT/TIG domains in the extracellular region of both proteins. Both tgrB1 and tgrC1 share the same transcriptional promoter and their spatiotemporal expression pattern is identical during development. We also examined the assembly of TgrC1-TgrB1 complexes via the split green fluorescence protein complementation assay and the fluorescence resonance energy transfer approach. Whereas TgrC1 is capable of forming cis-homodimers spontaneously, cis-homodimerization of TgrB1 depends on its trans-interaction with TgrC1. A model of the assembly process has been proposed.
To investigate signalling events initiated by the interaction between TgrB1 and TgrC1, pull-down assays were employed and led to the identification of myosin heavy chain kinase C as the cytoplamic partner of TgrC1. Mutational analysis showed that the basic residues in the short cytoplasmic domain of TgrC1 are critical to the binding with MHCK-C. Disruption of the interation between MHCK-C and TgrC1 results in an alteration of cell motility at the aggregation stage and aberrant cell sorting in slugs. These studies have highlighted the role of TgrB1-TgrC1 complexes in the regulation of morphogenesis during Dictyostelium development.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/44106 |
| Date | 27 March 2014 |
| Creators | Chen, Gong |
| Contributors | Siu, Chi-Hung |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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