Steven Spiker

Office: 3526C Gardner Hall, 919-515-5760
Lab: 3526 Gardner Hall, 919-515-5767
Steven_Spiker@ncsu.edu
Visit Our Lab Home Page

Plant molecular biology, chromatin structure, gene regulation

The thrust of the research in my laboratory is the role of chromatin structure in the control of gene expression in higher plants. In order for genes to be expressed, transcription factors and RNA polymerases must bind to control sequences. These sequences are normally inaccessible due to the structure of chromatin. What changes in chromatin structure are necessary to unblock the control sequences? How do these changes occur? In order to approach these questions, we study the physical properties of histones and interactions of these proteins, the major protein components of chromosomes, with DNA. We also study a group of chromosomal proteins, the HMG proteins, which have been implicated as structural proteins of transcriptionally active chromatin.

For the last several years we have focused on the MAR (matrix attachment region) DNA sequences that anchor chromatin fibers to the nuclear matrix and generate domains that can have either a transcriptionally active or inactive structure as depicted in Figure A (above). In this figure the solid blue bar represents a fiber of the nuclear matrix. The yellow boxes represent MAR sequences. In the domain on the left, DNA is organized into nucleosome fibers to form a relatively open structure that is accessible to transcription factors. In the domain on the right, the nucleosome fibers are supercoiled to form an inaccessible, transcriptionally inactive chromatin fiber.

The chromatin domains shown in Figure A are relevant to the "position effect" model to explain the low and variable expression of introduced genes in transgenic plants and animals. According to this model, if a transgene becomes incorporated into an inactive domain (like the one on the right), it would be transcribed at a very low rate or not at all. To test this model, we have made DNA constructs in which a transgene is flanked by a cloned MAR from tobacco plants (red boxes in Figure B). This construct is then introduced into tobacco cells in culture using the "gene gun." Expression of the transgene is measured and compared to expression from a control construct, which lacks the flanking MAR sequences. According to our model as depicted in Figure B, the cloned MAR sequences would allow the transgene to form an independent and transcriptionally active domain that would be free of the influence of the chromatin domain into which it became incorporated. In support of this model, we observe that the level of gene expression in the MAR-flanked transgene is much greater than that of controls lacking MARs. We are now investigating the mechanism of how such transcriptionally active, independent domains might be formed, and we are exploiting MAR sequences to make plants that express transgenes at high levels.

Selected Publications:

Bode, J., Winkelmann, S., Götze, S., Spiker, S., Tsutsui, K., Chengpeng, B., Prashanth, A.K., and Benham, C. (2006). Correlations between Scaffold/Matrix Attachment Region (S/MAR) binding activity and DNA duplex destabilization energy. J. Mol. Biol. 358: 597–613.

Thompson, W.F., Spiker, S., and Allen, G.C. (2006). Matrix Attachment Regions and transcriptional gene silencing. Annual Plant Reviews. 29: 136–161 (in Annual Plant Reviews, Regulation of Transcription in Plants, K. Grasser, ed. Blackwell).

Francis, K.E., and Spiker, S. (2005). Identification of Arabidopsis thaliana transformants without selection reveals a high occurrence of silenced T-DNA integrations. The Plant Journal. 41: 464–477. [pdf]

Move directly to the Genetics Home Page.
Move directly to the CALS Home page.

Comments should be sent to theDepartment of Genetics
Genetics Web display last changed 1 December 2008.