ARTICLE

COMPARTMENTALIZATION OF THE DEVELOPING MACRONUCLEUS FOLLOWING CONJUGATION IN STYLONYCHIA AND EUPLOTES

John A. Kloetzel ¹

¹ From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80302.

Dr. Kloetzel's present address is the Department of Biological Sciences, University of Maryland-Baltimore County, Baltimore, Maryland 21228

The development of the macronucleus following conjugation in the hypotrichous ciliates Euplotes and Stylonychia has been examined with the electron microscope. Banded polytene chromosomes can be seen in thin sections of the macronuclear anlagen during the early periods of exconjugant development. As the chromosomes reach their maximum state of polyteny, sheets of fibrous material appear between the chromosomes and transect the chromosomes in the interband regions. Individual bands of the polytene chromosomes thus appear to be isolated in separate compartments. Subsequently, during the stage when the bulk of the polytenic DNA is degraded (1), these compartments swell, resulting in a nucleus packed with thousands of separate spherical chambers. Individual chromosomes are no longer discernible. The anlagen retain this compartmentalized condition for several hours, at the end of which time aggregates of dense material form within many of the compartments. The partitioning layers disperse shortly before replication bands appear within the elongating anlagen, initiating the second period of DNA synthesis characteristic of macronuclear development in these hypotrichs. The evidence presented here suggests that the "chromatin granules" seen in the mature vegetative macronucleus represent the material of single bands of the polytene chromosomes seen during the earlier stages of macronuclear development. The possibility is also discussed that the degradation of DNA in the polytene chromosomes may be genetically selective, which would result in a somatic macronucleus with a different genetic constitution than that of the micronucleus from which it was derived.

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This article has been cited by other articles:

• Postberg, J., Alexandrova, O., Cremer, T., Lipps, H. J. (2005). Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription. J. Cell Sci. 118: 3973-3983 [Abstract] [Full Text]  
• Maercker, C., Kortwig, H., Nikiforov, M. A., Allis, C. D., Lipps, H. J. (1999). A Nuclear Protein Involved in Apoptotic-like DNA Degradation in Stylonychia: Implications for Similar Mechanisms in Differentiating and Starved Cells. Mol. Biol. Cell 10: 3003-3014 [Abstract] [Full Text]  
• Prescott, D. M., Murti, K. G. (1974). Chromosome Structure in Ciliated Protozoans. Cold Spring Harb Symp Quant Biol 38: 609-618 [Abstract]  

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