October 2, 2014
Written by Samia Ayew, Biology Major
On Friday, March 21 2014 at about 11AM, I received the wonderful news that the Deutsche Akademischer Austauch Dienst (German Academic Exchange Service) had awarded me with a scholarship to undertake a practical training in Biology in Berlin, Germany. The internship lasted for three months at the German Rheumatism Research Center (DRFZ) located on the grounds of Charité, a historical University Hospital. I worked with Kerstin Westendorf, a PhD student, who had designed a project for us to investigate the flanking sequences of the cre gene in rheumatoid arthritis transgenic mouse models using the long inverse polymerase chain reaction technique (IPCR). The Cre-Lox system was originally taken from the bacteriophage P1, which uses this system to integrate itself into the bacterial genome and exit it again. In research, the Cre-lox system has been adopted as a sophisticated tool for generating knockouts, conditional knockouts and reporter strains. The gene of interest is flanked by loxP sites or a floxed stop cassette is inserted in front of it in the transgenic mice, which are then bred with a strain of mice expressing cre-recombinase (a site-specific DNA recombinase encoded by the cre gene) under the control of a cell type specific promoter. In our lab, we were using CD4cre mice that express cre-recombinase under the control of the CD4 promoter, which is mainly active in T helper cells. These mice were not generated by knock-in (insertion of a protein coding cDNA sequence at a specific locus in an organism’s chromosome) because the mice still need to normally express the CD4 gene. Thus, the construct was inserted randomly and a founding line was selected for good and stable expression with minimal leakiness (i.e. unspecific expression). As a result, the point of integration of the cre gene in the mice genome is unknown. However, after conducting a series of experiments involving the long IPCR technique, we were able to determine that the human growth hormone gene flanked the cre gene upstream in the CD4cre mouse genome.
What really fascinated me was the depth of history carved on the red Gothic brick walls of the Charité campus. The DRFZ neighbored the Berlin Museum of Medical History that housed Rudolf Virchow’s famous pathological specimen collection. Interning on the very grounds that had witnessed so much history from the Black plague to the two World Wars left me with a strong impression. To start my day, I first planned and organized the experiments I had to conduct. After meticulously calculating the volumes of solutions I needed to prepare ahead of time, I slipped on my lab coat and walked over to the actual laboratory. Some of the lab techniques I learned included isolating DNA from mouse tissues, performing standard PCRs to genotype the transgenic mice, running gel electrophoresis, digesting DNA with restriction enzymes, and DNA ligation clean ups. By the end of my three-month internship, these techniques had almost become second nature. Indeed, I found it a greatly rewarding experience both on a scientific and personal level. During the long weekends I travelled to other cities in Germany like Dresden, Heidelberg, Görlitz, Münich, and neighboring European cities like Brussels and Paris. I came learned so much about myself, one of the most important being stress management in the lab as well as on the streets of Berlin. I am very thankful to have been blessed with this opportunity of a lifetime!