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Abstract
ABSTRACTOne of the most dramatic examples of nuclear morphogenesis occurs during conjugation in Tetrahymena when the micronucleus elongates to a size longer than the cell itself. After contraction to a spherical shape, the nucleus moves directly to chromosome separation in the first meiotic division. Here we investigate the consequences of interrupting the elongation process. Colchicine, a microtubule inhibitor, caused retraction of elongated structures. With time, cells began to lose their micronuclei, and by five hours more than half of the paired cells had at least one cell missing a micronucleus. After reversing the colchicine block, existing micronuclei did not undergo elongation again, nor did meiosis occur. These observations indicate that micronuclear elongation is critical to subsequent meiotic division. Further, nuclear elimination occurs, which could be due to meiotic failure or possibly a problem downstream from meiosis. An analysis of the process of colchicine-induced micronuclear degeneration indicated that it was regulated by a caspase-dependent mechanism, characteristic of apoptosis, and then resorbed by a lysosome-dependent autophagic mechanism. Amicronucleate cells failed to grow when returned to nutrient medium, likely because of a lesion in the post-conjugation reconstruction of a functioning oral apparatus. The ease by which a large number of nuclei are induced to “self-destruct” may make this system useful in investigating the link between colchicine treatment and nuclear death in Tetrahymena, and in investigating how nuclear death could be regulated in living cells more generally. Finally, we note that this phenomenon might relate to the evolution of amicronucleate species of Tetrahymena.
Highlights
The size and shape of a nucleus is a phenotypic characteristic of the cell in which it is located (Georgatos, 1994)
We found that, in Tetrahymena, micronuclear elongation is of critical importance
When cells are exposed to colchicine, elongation and meiosis are blocked, and the cells cannot progress through conjugation
Summary
The size and shape of a nucleus is a phenotypic characteristic of the cell in which it is located (Georgatos, 1994). Correct morphogenesis of nuclei can be critical for development, such. Received 20 January 2014; Accepted 13 February 2014 as in the differentiation of sperm cells (Dadoune, 1995) and during cellularization of the cortex in Drosophila embryos (Pilot et al, 2006). Nuclear change shape takes place during the epithelia-to-mesenchyme transition in tumor cells, and may contribute to metastasis (Thiery et al, 2009; Yao et al, 2011)
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