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Eukaryotic Cell, February 2007, p. 271-279, Vol. 6, No. 2
1535-9778/07/$08.00+0     doi:10.1128/EC.00235-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Analysis of Thalassiosira pseudonana Silicon Transporters Indicates Distinct Regulatory Levels and Transport Activity through the Cell Cycle{triangledown}

Kimberlee Thamatrakoln{dagger} and Mark Hildebrand*

Marine Biology Research Division, Scripps Institution of Oceanography, 9500 Gilman Dr., La Jolla, California 92093-0202

Received 18 July 2006/ Accepted 6 December 2006

An analysis of the expression and activity of silicon transporters (SITs) was done on synchronously growing cultures of the diatom Thalassiosira pseudonana to provide insight into the role these proteins play in cellular silicon metabolism during the cell cycle. The first SIT-specific polyclonal peptide antibody was generated and used in the immunoblot analysis of whole-cell protein lysates to monitor SIT protein levels during synchronized progression through the cell cycle. Peaks in SIT protein levels correlated with active periods of silica incorporation into cell wall substructures. Quantitative real-time PCR on each of the three distinct SIT genes (TpSIT1, TpSIT2, and TpSIT3) showed that mRNA levels for the most highly expressed SIT genes peaked during the S phase of the cell cycle, a period prior to maximal silicon uptake and during which cell wall silicification does not occur. Variations in protein and mRNA levels did not correlate, suggesting that a significant regulatory step of SITs is at the translational or posttranslational level. Surge uptake rates also did not correlate with SIT protein levels, suggesting that SIT activity is internally controlled by the rate of silica incorporation. This is the first study to characterize SIT mRNA and protein expression and cellular uptake kinetics during the course of the cell cycle and cell wall synthesis, and it provides novel insight into SIT regulation.

* Corresponding author. Mailing address: Marine Biology Research Division, Scripps Institution of Oceanography, 9500 Gilman Dr., MC 0202, La Jolla, CA 92093-0202. Phone: (858) 822-0167. Fax: (858) 534-7313. E-mail: mhildebrand{at}ucsd.edu.

{triangledown} Published ahead of print on 15 December 2006.

{dagger} Present address: Institute of Marine and Coastal Studies, Rutgers University, 71 Dudley Rd., New Brunswick, NJ 08901.

Eukaryotic Cell, February 2007, p. 271-279, Vol. 6, No. 2
1535-9778/07/$08.00+0     doi:10.1128/EC.00235-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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