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Eukaryotic Cell, October 2004, p. 1101-1110, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1101-1110.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Transcriptional Transitions during Dictyostelium Spore Germination{dagger}

Qikai Xu,1,2 Miroslava Ibarra,2,{ddagger} Dana Mahadeo,3,{ddagger},§ Chad Shaw,2 Eryong Huang,1,2 Adam Kuspa,2,4 David Cotter,3 and Gad Shaulsky1,2*

Graduate Program in Structural and Computational Biology and Molecular Biophysics,1 Department of Molecular and Human Genetics,2 Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas,4 Department of Biological Sciences, University of Windsor, Windsor, Ontario, Canada3

Received 30 January 2004/ Accepted 12 July 2004

Many protozoa form spores in response to adversity; therefore, spore germination is a key process in their life cycle. Dictyostelium discoideum sporulates in response to starvation following a developmental program. Germination is characterized by two visible changes, spore swelling and the emergence of amoeba from the spore capsule. Several studies have indicated that an additional process termed spore activation is also required, but the physiological changes that characterize the three phases are largely uncharacterized. We used microarrays to monitor global transcriptional transitions as a surrogate measure of the physiological changes that occur during germination. Using two independent methods to induce germination, we identified changes in mRNA levels that characterized the germination process rather than changes that resulted from the induction method. We found that germination is characterized by three transitions. The first transition occurs during activation, while the spores appear dormant, the largest transition occurs when swelling begins, and the third transition occurs when emergence begins. These findings indicate that activation and swelling are not passive occurrences, such as dilution of inhibitors or spore rehydration, but are active processes that are accompanied by dramatic events in mRNA degradation and de novo transcription. These findings confirm and extend earlier reports that genes such as celA are regulated during spore germination. We also found by mutation analysis that the unconventional myosin gene myoI, which is induced during early germination, plays roles in the maintenance of dormancy and in spore swelling. This finding suggests that some of the observed transcriptional changes are required for spore germination.

* Corresponding author. Mailing address: Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: (713) 798-8082. Fax: (713) 798-1021. E-mail: gadi{at}bcm.tmc.edu.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

{ddagger} M.I. and D.M. contributed equally to this work.

§ Present address: National Cancer Institute, National Institutes of Health, Bethesda, MD 20814.

Eukaryotic Cell, October 2004, p. 1101-1110, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1101-1110.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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