Colchicine-induced degeneration of the micronucleus during conjugation in Tetrahymena

Pin-Fang Chen; Sita Singhal; Daniel Bushyhead; Sarabeth Broder-Fingert; Jason Wolfe

doi:10.1242/bio.20147708

Colchicine-induced degeneration of the micronucleus during conjugation in Tetrahymena

Biol Open. 2014 Apr 11;3(5):353-61. doi: 10.1242/bio.20147708.

Authors

Pin-Fang Chen¹, Sita Singhal², Daniel Bushyhead³, Sarabeth Broder-Fingert⁴, Jason Wolfe⁵

Affiliations

¹ Present address: Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
² Present address: Internal Medicine Residency Program, University of Connecticut Health Center, Farmington, CT 06030, USA.
³ Present address: School of Medicine, University of Washington, Seattle, WA 98195, USA.
⁴ Present address: Department of Pediatrics, Massachusetts General Hospital, Boston, MA 02114, USA.
⁵ Department of Biology, Wesleyan University, Middletown, CT 06459, USA Present address: Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030, USA. Present address: Internal Medicine Residency Program, University of Connecticut Health Center, Farmington, CT 06030, USA. Present address: School of Medicine, University of Washington, Seattle, WA 98195, USA. Present address: Department of Pediatrics, Massachusetts General Hospital, Boston, MA 02114, USA. jwolfe@wesleyan.edu.

Abstract

One 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.

Keywords: Apoptosis; Autophagy; Ciliate; Meiosis; Micronucleus; Nuclear morphogenesis; Tetrahymena.