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Geoffrey Kapler

Kapler, Geoffrey
Geoffrey Kapler
Professor Chair Department of Molecular and Cellular Medicine and Professor of Biochemistry & Biophysics
Reynolds / Room 455
Undergraduate Education
B.S. University of Connecticut (1979)
Graduate Education
Ph.D. Harvard University (1989)
Postdoc. University of California, San Francisco (1990-94)
Joined Texas A&M in 1994

DNA Replication / Gene Amplification / Replication Proteins

DNA replication initiates at specific chromosomal sites termed origins of replication. Whereas regulatory proteins restrict replication to once per cell cycle division, cell cycle control can be overridden during development and tumorigenesis in humans. We are studying a process, termed gene amplification, inTetrahymena thermophila which selectively amplifies the naturally-occurring ribosomal DNA (rDNA) minichromosome 10,000-fold within a single S phase. Using biochemical, molecular, and genetic approaches to identify and characterize cis-acting determinants and trans-acting regulatory proteins, we have uncovered a complex regulatory pathway that involves proteins that compete for binding to the same cis-acting sequence elements. One of these activities, TIF4, appears to be the equivalent of the phylogenetically-conserved yeast origin recognition complex (ORC). Another activity, TIF1, selectively modulates the access of trans-acting replication and transcription activators to disperse determinants that control both processes. Using an antisense ribosome strategy to block expression of the recently cloned TIF1 gene, we demonstrate that TIF1 establishes the precisely defined chromatin structure at the rDNA replication origin. Recent experiments also uncovered an amplification-specific cis-acting determinant that might facilitate the selective recruitment ORC to the rDNA replicon during programmed gene amplification.

Recent Publications

  1. Feng, L, Wang, G, Hamilton, EP, Xiong, J, Yan, G, Chen, K et al.. A germline-limited piggyBac transposase gene is required for precise excision in Tetrahymena genome rearrangement. Nucleic Acids Res. 2017;45 (16):9481-9502.
    doi: 10.1093/nar/gkx652. PubMed PMID:28934495. PubMed Central PMC5766162.

  2. Sandoval, PY, Lee, PH, Meng, X, Kapler, GM. Checkpoint Activation of an Unconventional DNA Replication Program in Tetrahymena. PLoS Genet. 2015;11 (7):e1005405.
    doi: 10.1371/journal.pgen.1005405. PubMed PMID:26218270. PubMed Central PMC4517752.

  3. Lee, PH, Meng, X, Kapler, GM. Developmental regulation of the Tetrahymena thermophila origin recognition complex. PLoS Genet. 2015;11 (1):e1004875.
    doi: 10.1371/journal.pgen.1004875. PubMed PMID:25569357. PubMed Central PMC4287346.

  4. Gao, S, Xiong, J, Zhang, C, Berquist, BR, Yang, R, Zhao, M et al.. Impaired replication elongation in Tetrahymena mutants deficient in histone H3 Lys 27 monomethylation. Genes Dev. 2013;27 (15):1662-79.
    doi: 10.1101/gad.218966.113. PubMed PMID:23884606. PubMed Central PMC3744725.

  5. Donti, TR, Datta, S, Sandoval, PY, Kapler, GM. Differential targeting of Tetrahymena ORC to ribosomal DNA and non-rDNA replication origins. EMBO J. 2009;28 (3):223-33.
    doi: 10.1038/emboj.2008.282. PubMed PMID:19153611. PubMed Central PMC2637336.

  6. Mohammad, MM, Donti, TR, Sebastian Yakisich, J, Smith, AG, Kapler, GM. Tetrahymena ORC contains a ribosomal RNA fragment that participates in rDNA origin recognition. EMBO J. 2007;26 (24):5048-60.
    doi: 10.1038/sj.emboj.7601919. PubMed PMID:18007594. PubMed Central PMC2140106.

  7. Yakisich, JS, Sandoval, PY, Morrison, TL, Kapler, GM. TIF1 activates the intra-S-phase checkpoint response in the diploid micronucleus and amitotic polyploid macronucleus of Tetrahymena. Mol. Biol. Cell. 2006;17 (12):5185-97.
    doi: 10.1091/mbc.e06-05-0469. PubMed PMID:17005912. PubMed Central PMC1679683.

  8. Yakisich, JS, Kapler, GM. Deletion of the Tetrahymena thermophila rDNA replication fork barrier region disrupts macronuclear rDNA excision and creates a fragile site in the micronuclear genome. Nucleic Acids Res. 2006;34 (2):620-34.
    doi: 10.1093/nar/gkj466. PubMed PMID:16449202. PubMed Central PMC1356531.

  9. Morrison, TL, Yakisich, JS, Cassidy-Hanley, D, Kapler, GM. TIF1 Represses rDNA replication initiation, but promotes normal S phase progression and chromosome transmission in Tetrahymena. Mol. Biol. Cell. 2005;16 (6):2624-35.
    doi: 10.1091/mbc.e05-02-0107. PubMed PMID:15772155. PubMed Central PMC1142411.

  10. Smith, JJ, Yakisich, JS, Kapler, GM, Cole, ES, Romero, DP. A beta-tubulin mutation selectively uncouples nuclear division and cytokinesis in Tetrahymena thermophila. Eukaryotic Cell. 2004;3 (5):1217-26.
    doi: 10.1128/EC.3.5.1217-1226.2004. PubMed PMID:15470250. PubMed Central PMC522614.

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