Post-transcriptional Regulation of S-Phase Genes in the Dinoflagellate, Karenia brevis

Authors

  • STEPHANIE A. BRUNELLE,

    1. Marine Biotoxins Program, NOAA Center for Coastal Environmental Health and Biomolecular Research, Charleston, South Carolina 29412
    2. Marine Biomedical and Environmental Sciences Program, Medical University of South Carolina, Charleston, South Carolina 29412
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  • FRANCES M. VAN DOLAH

    1. Marine Biotoxins Program, NOAA Center for Coastal Environmental Health and Biomolecular Research, Charleston, South Carolina 29412
    2. Marine Biomedical and Environmental Sciences Program, Medical University of South Carolina, Charleston, South Carolina 29412
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Corresponding Author: Frances M. Van Dolah, Marine Biotoxins Program, NOAA Center for Coastal Environmental Health and Biomolecular Research, 219 Fort Johnson Road, Charleston, South Carolina 29412—Telephone number: +1 843 725 4864; FAX number: +1 843 762 8700; e-mail: fran.vandolah@noaa.gov

Abstract

ABSTRACT. Karenia brevis is a toxic dinoflagellate responsible for red tides in the Gulf of Mexico. The molecular mechanisms controlling its cell cycle are important to bloom formation because blooms develop through vegetative cell division. This study identifies a suite of conserved S-phase genes in K. brevis—proliferating cell nuclear antigen (PCNA), ribonucleotide reductase 2, replication factor C, and replication protein A—and characterizes their expression at the mRNA and protein level over the cell cycle. In higher eukaryotes, the expression of these genes is controlled by transcription, activated at S-phase entry by the E2F transcription factor, which ensures their timely availability for DNA synthesis. In the dinoflagellate, these transcripts possess a 5′-transspliced leader sequence, which suggests they may be under post-transcriptional control as demonstrated in trypanosomes. Using quantitative polymerase chain reaction (qPCR), we confirmed that their transcript levels are unchanged over the cell cycle. However, their proteins are maximally expressed during S-phase. This suggests their cell-cycle-dependent expression may be achieved at the level of translation and/or stability. Proliferating cell nuclear antigen further undergoes an increase in size of ∼9 kDa that dominates during S-phase. This coincides with a change in its distribution, with prominent staining of chromatin-bound PCNA occurring during S-phase. We hypothesize that the change in the observed size of PCNA is due to post-translational modification. Together, these studies demonstrate post-transcriptional regulation of S-phase genes in K. brevis. Differential expression of these S-phase proteins may be useful in the development of biomarkers to assess bloom growth status in the field.

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