Acquisition of cell polarity during cell cycle and oral replacement in Tetrahymena

Abstract

The aim of this study was to search for a mechanism responsible for the acquisition of cell polarity in a ciliate Tetrahymena. Homologs of the mammalian genes coding for CDC42-GSK3β-MARK/PAR1-MAPs proteins were found in the Tetrahymena genome (Eisen et al., 2006, and this study). These proteins belong to a pathway which controls assembly and disassembly of microtubule bundles and cell polarity in neural cells. In Tetrahymena, there are two types of morphogenesis: divisional and oral replacement (OR). In divisional morphogenesis, an elongation of longitudinal microtubule bundles (LMs) takes place during cell division. In contrast, in OR type morphogenesis, which occurs in starved non-dividing cells, a polar retraction of LMs occurs. In T. pyriformis, the frequency of developmental switch to OR morphogenesis increases in the presence of wortmannin, an inhibitor of the CDC42-GSK3β-MARK pathway. In contrast, wortmannin when applied to dividing cells does not affect divisional morphogenesis. Using immunostaining with the antibody against mammalian mitotic phosphoproteins (MPM-2) we show that these proteins co-localize with the LMs and are distributed along the anterior-posterior gradient. In addition, we show that during OR type morphogenesis, the fate of LMs correlates with the anterior-posterior gradient of instability of the cortical structures. We used the conditional mouthless mutant of T. thermophila (Tiedtke et al., 1988) to test if the presence of the oral apparatus is required for the maintenance of cell polarity. We discuss our results in relation to the hypothesis of GSK3-β-MARK pathway involvement in the acquisition of cell polarity in Tetrahymena. KEY WORDS: Tetrahymena, polarity, cytoskeleton, MARK, armadilloThe Tetrahymena (like other ciliates) is a permanently polarized cell. Longitudinal ciliary rows (CR) define its anterior-posterior axis and a sub-apically located oral apparatus (OA) marks its ventral side. The position of other cortical structures depends on the position of the oral apparatus (Frankel 1999) (Fig. 1A and Fig. 7A). In Tetrahymena the spatial deployment of the cytoskeletal proteins is under genetic control of a mechanism of global positioning (Kaczanowski 1975, Williams et al., 1987, JerkaDziadosz et al., 1995, Kaczanowska et al., 2003, StrzyzewskaJowko et al., 2003. The aim of the present study was to gain an insight into the mechanism responsible for the acquisition and maintenance of cell polarity, during morphogenesis of Tetrahymena.In Tetrahymena there are two types of morphogenesis: divisional and oral replacement (OR). The cortex of Tetrahymena contains a regular array of polarized longitudinal microtubular Int. J. Dev. Biol. 52: 249-258 (2008) Abbreviations used in this paper: AF, anarchic field of oral primordium; CR, ciliary rows of basal body units; CVP, the contractile vacuole pore located at the posterior area of the cell to the right of the ventral side; EHT, end of heat treatment; LM, Longitudinal microtubule bands; nOA, newly formed oral apparatus that a...

What Do Genic Mutations Tell Us about the Structural Patterning of a Complex Single-Celled Organism?

“…According to the original authors, "The oral structures are missing often at 37°C, but present at 28°C" (154). More recently, this mutant was described as being "able to proliferate [in enriched medium at 37°C] yielding small cells with very variable phenotypes including some cells without oral apparatuses and some cells in OR [oral replacement] morphogenesis" (88). This strain was also sent to us, and we were unable to obtain progeny following crosses; we also found that the II8G cells produced silver-and protargol-stainable oral structures no matter how long the cells were kept at 39°C (Fig.…”

Polarity in Ciliate Models: From Cilia to Cell Architecture

“…However, there is the possibility that other kinases operate upstream of the Hippo pathway, for example creating a first wave of signaling required for the recruitment of the Hippo components to specific localizations. In Tetrahymena there are evidences that support the hypothesis that GSK3β (Glycogen synthase kinase 3s)-MARK/MAPs signaling pathway may be involved in the establishment of global cell polarity (Kaczanowska et al, 2008). Although Tetrahymena genome does not seem to encode the components of a Wnt signaling pathway, that operate upstream of this signaling, the orthologs of the GSK3β-MARK2/PAR-1 pathway were identified (Kaczanowska et al, 2008).…”

“…Noticeable is the fact that the guanine nucleotide exchanger Dock6 is simultaneously specific for the signaling of protein Rac1 and for the rho-type GTPase Cdc42. The GTPase Cdc42 is an essential conserved factor in controlling eukaryotic cell polarity that its encoded by a gene present in the genome of Tetrahymena (Miyamoto et al, 2007; Kaczanowska et al, 2008). Although it is uncertain if these complexes participate in Hippo signaling pathway, this shows that Mob1 regulation and activity is much more complex than previously predicted.…”

Mutual antagonism between Hippo signaling and cyclin E drives intracellular pattern formation

“…T. thermophila lacks orthologues of most of the Par network proteins, with the exception of CDC42 (TTHERM_00267910). Also, TTHERM_01017250 has weak similarity to PAR-1 (Kaczanowska et al, 2008). Despite the limited conservation of the Par network, the logic of cell polarization, based on cortical mutual cortical subdivision (right) in dividing cells grown at 39°C for 3.5 h. The numbers of scored cells are indicated.…”