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Abstract
Not much has been revealed about how organelles are assembled into patterns inside cells. Ciliates are good models to study intracellular pattern formation due to the complex cortical pattern on the cell surface that is accurately replicated during cell division. For example, in Tetrahymena thermophila, the feeding organelle oral apparatus is located near the anterior cell end, and the oral primordium (new oral apparatus) is formed at ciliary row posterior to the old oral apparatus. The contractile vacuole pores, organelles required for osmoregulation, are located near the posterior cell end and on the cell’s right side (cell’s perspective). The goal of my doctoral research was to characterize gene products implicated in intracellular pattern formation in T. thermophila. In my first project, I characterized the cdaH-1 mutant that displays a pleiotropic phenotype with multiple defects in anterior-posterior patterning. We found that CdaH is a Tetrahymena ortholog of conserved Fused/Stk36 kinases. CdaH plays multiple roles in patterning on both global and local scale. The global function of CdaH is in maintaining the subequatorial position of the oral primordium. The local functions of CdaH include induction of the division boundary, generation of new cell ends, cytokinesis and stability of the oral primordium. CdaH prominently colocalized with the contractile ring, implying a possibility that its ancestral function is associated with actin. In my second project, I characterized the hpo1 mutants that are affected in patterning on the circumferential axis. Loss-of-function of Hpo1 caused displacement and excessive number of oral primordia. We discovered that Hpo1 is an Armc9-like protein that accumulates on the cell’s right side, as a bidirectional gradient with drop-offs in concentration on the ventral and dorsal side. Our data indicate that Hpo1 functions as a bilateral repressor that spatially excludes oral development from its domain. That Hpo1 marks the position for extra oral apparatus formed on the dorsal side of janus mutant reflects the role of Hpo1 as the bilateral repressor. Double mutants lacking Hpo1 and Bcd1 display diverse patterning defects, including elongated cell morphology. Overall, we conclude that circumferential patterning in Tetrahymena involves multiple factors that are localized as gradients.