Geoffrey Kapler

Geoffrey Kapler

Professor, Chair

Department of Molecular and Cellular Medicine, Member of the GSBS Faculty
Room 440 Reynolds Medical Building / Lab Room 455
College Station, TX   77843

Phone: 979.436.0859
Fax: 979.847.9481

Education and Post-Graduate Training

Dr. Geoffrey Kapler received his BS in biology from the University of Connecticut in 1979 and his PhD in genetics from Harvard University in 1989, working with Stephen Beverley. He did his postdoctoral research with the 2009 Nobel Laureate in Medicine, Elizabeth Blackburn, at the University of California, San Francisco. He joined the faculty at Texas A&M in 1994. Kapler is also a Member of Biochemistry and Biophysics and served as the chair of the Interdisciplinary Program in Genetics. In 2007 he was named associate department head. In 2010 he was named interim departmental chair. Kapler has served as the Departmental Chair of Molecular & Cellular Medicine since 2012. He was appointed the Tom and Jean McMullin Professor of Genetics in January 2012. He has taught courses in medical genetics, yeast genetics, the cell cycle and chromosome biology.

Research Interests

Kapler’s broad research interests are concerned with the replication and transmission of eukaryotic chromosomes. The failure to completely replicate the genome during S phase or partially re-replicate chromosomes leads to genome instability- a hallmark of cancer cells. The central questions investigated in the laboratory are concerned with how replication initiation sites are established in chromosomes and how they are regulated during conventional (G1/S/G2/M) and alternative cell cycles, including endoreplication (gap-S-gap-S...) and locus-specific gene amplification. The laboratory uses the early branching model eukaryote, Tetrahymena thermophila, as its model system to study these questions. As a member of the Ciliophora lineage, Tetrahymena contains two nuclei within each cell, the diploid germline micronucleus and polyploid somatic macronucleus. The complex developmental program that generates a new macronucleus in exconjugants has provided fertile ground for studying the differential regulation of replication origin usage. A strength of the model system is Tetrahymena’s ability to support replication of naturally occurring and artificially engineered minichromosomes. These features have provides excellent opportunities to use forward and reverse genetic approaches to identify and characterize cis-acting determinants and trans-acting regulatory factors. While Tetrahymena employs conserve eukaryotic DNA replication machinery, including the origin recognition complex (ORC) and MCM2-7 replicative helicase, we have discovered novel regulatory factors, including an RNA molecule that selectively targets ORC to origins of replication in the rDNA minichromsome, which is amplified 9000-fold during development.

The current focus of the lab is to use high throughput (nascent strand) DNA sequencing to generate a comprehensive map of replication initiation sites under different physiological conditions. We recently reported that ORC and MCM protein levels are reduced >50-fold under conditions of replication stress, and that upon removal of the stressor, cells replicate their entire macronuclear genome prior to replenishment of ORC and MCM subunits. Known origins are inactive during this highly unconventional S phase, yet new initiation events generate bidirectional replication forks and faithfully replicate chromosomes. Comparative analysis of origin usage under high and low ORC conditions should reveal ORC-dependent and ORC-independent replication initiation sites. Functional assays will be used to determine the underlying mechanism for ORC-independent replication initiation.

The laboratory takes advantage of powerful molecular and genetic tools available in the Tetrahymena model system, including classic genetic analysis, an array of approaches for making gene knockouts and replacements, the ability to synchronize the cell cycle and development, single molecule DNA fiber imaging, molecular approaches to visualize DNA replication intermediates, high throughput RNA-Seq and nascent strand DNA sequencing. Finally, the functional analysis of genetically modified Tetrahymena is used to test models and has established new paradigms in the DNA replication field.


  • Sandoval PY, Lee, PH, Meng X, and Kapler GM. (2015) Checkpoint Activation of an Unconventional DNA Replication Program in Tetrahymena. PLoS Genet. 11(7):e1005405. doi: 10.1371/journal.pgen.1005405. eCollection 2015 Jul. PMID: 26218270
  • Lee PH, Meng X, and Kapler GM. (2015) Developmental Regulation of the Tetrahymena thermophila Origin Recognition Complex. PLoS Genet. 11(1):e1004875. doi: 10.1371/journal.pgen.1004875. eCollection 2015 Jan. PMID: 25569357
  • Gao S, Xiong J, Zhang C, Berquist BR, Yang R, Zhao M, Molascon AJ, Kwiatkowski SY, Yuan D, Qin Z, Wen J, Kapler GM, Andrews PC, Miao W, and Liu Y. (2013) Impaired replication elongation in Tetrahymena mutants deficient in histone H3 Lys 27 monomethylation. Genes Dev. 27(15):1662-79. doi: 10.1101/gad.218966.113. Epub 2013 Jul 24. PMID: 23884606
  • Donti, T.R., Datta, S., Sandoval, P.Y., and Kapler, G.M. (2009) Differential targeting of Tetrahymena ORC to ribosomal DNA and non-rDNA replication origins. EMBO J. 28(3): 223-233. PMID: 19153611
  • Mohammad, M.M., Smith, A.G., Donti, T.R., and Kapler, G.M. (2007) Tetrahymena ORC contains a ribosomal RNA fragment that participates in rDNA origin recognition. EMBO Journal. 26,5048-5060. PMID: 18007594
  • Yakisich, J.S., and Kapler, G.M. (2006) 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. 34, 620-634. PMID: 16449202
  • Yakisich, J.S., Sandoval, P.Y., Morrison, T.L., and Kapler, G.M. (2006) TIF1 activates the intra-S phase checkpoint response in the diploid micronucleus and amitotic polyploid macronucleus of Tetrahymena. Molecular Biology of the Cell. 17,5185-5197. PMID: 17005912
  • Morrison, T.L., Yakisich, J.S., Cassidy-Hanley, D., and Kapler, G.M. (2005) TIF1 represses rDNA replication initiation, but promotes normal S phase progression and chromosome transmission in Tetrahymena. Mol. Biol. Cell. 16, 2624-2635. PMID: 15772155
  • Smith, J.J., Yakisich, J.S., Kapler, G.M., Cole, E.S., and Romero, D.P. (2004) A beta-tubulin mutation selectively uncouples nuclear division and cytokinesis in Tetrahymena thermophila. Eukaryot Cell. 3,1217-1226. PMID: 15470250