Discovery and Implications of a new Variable Tandem Repeat in the Dopamine Transporter Gene

Li, Sally Shan
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • David J. Vandenbergh, Thesis Supervisor
  • Richard W. Ordway, Honors Advisor
  • Variable Number Tandem Repeat
  • VNTR
  • DAT1
  • SLC6A3
The Dopamine Transporter gene (DAT1 or SLC6A3) codes for a protein that controls the reuptake of dopamine into the presynaptic terminal, thus regulating dopamine activity. Published studies have linked VNTRs and polymorphisms in this gene to addiction, ADHD, schizophrenia, and bipolar disorder; similar association studies should be performed with this VNTR. The focus in this paper is the discovery of this VNTR from high variability observed between intron 6 and exon 8 which is seen in a pilot study by Southern Blot analysis following digestion with the TaqI restriction endonuclease. To determine whether the observed variability was due to highly polymorphic TaqI sites or other polymorphic sequences within that location, we applied a combination of molecular genetic techniques and bioinformatics. Two TaqI sites were identified that flank the polymorphic sequence. Each site was PCR amplified and then cut with TaqI to test for heterozygosity. Twenty individuals were tested and their TaqI sites were found to be nonpolymorphic across all samples. In a separate study, bioinformatic analysis was conducted on the region containing the polymorphic sequence from two haploid hydatidiform moles. A set of tandem repetitive elements was identified that is variable in copy number and thus represents a Variable Number of Tandem Repeats (VNTR). Experiments to determine the number of copies of the repeated sequence in different samples of DNA were made by PCR, but the site has been resistant to all modifications attempted. This site is important to characterize due to the potential role of this gene in many psychiatric disorders and behaviors.