Sensing the antisense: study of gene expression in differentiating leukemic cells by a quantifying method
Ismini Karakasilioti
Leukemia is a type of cancer that develops in the blood-forming tissues of humans and other animals and affects the development of immature blood cells into normal blood cells. As it accounts for almost 8% of all cancers and affects mainly children around the age of ten, it has been of major importance to understand the physiology of the disease, so as to be able to introduce rewarding therapies.
Any cancerous cell, as well as a leukemic cell, differs from any normal cell in the way that it has undergone many genetic changes. Such changes can be rearrangements of DNA sequences throughout the genome, deletions or duplications of several parts of the chromosomes and alteration in expression of several genes. Studies of these changes can reveal the way the physiology of the cell changes when it becomes cancerous. In consequence, they can evince new and important targets for cancer therapy.
During this project, the expression of a gene that is involved in regulation of cell growth was studied. When treated with a certain drug, the leukemic cells changed from their cancerous state towards a “normal” noncancerous state. This normalized state can be induced in vitro – in cell cultures used in the lab and not in living patients – by treating the cancerous cells with specific drugs, such as retinoic acid and 1,25-dihydroxy vitamin D3. This means that it would be possible to view if and how the expression of a specific gene changes when the leukemic cells became more normal. The aim was to monitor any possible differences in gene expression in leukemic cellsthat were treated with this drug, compared to untreeated leukemic cells.
More specifically, the level of gene expression that was studied was the regulation after the DNA had been transcribed into RNA, by a reaction between sense and antisense transcripts of the specific gene locus. The sense transcript is the RNA strand transcribed from the DNA sequence of a gene that is later translated into a protein (mRNA). The antisense transcript is the RNA strand that originates from the opposite DNA sequence of the same gene and, as a consequence, is complementary to the first strand. If these two strands are simultaneously present in a cell, they can bind to each other and noprotein will be made.
By a quantifying method, the abundance of these sense and antisense transcripts in leukemic cells was examined. It was possible to see that this specific gene – Cyclin A – was trasnccribed when the cells were leukemic. When normalized by the drug tratment, the cells showed very low levels of Cyclin A expression. This was true for both sense and antisense transcripts of the gene.
Degree project in biology, Autumn semester 2005
Examensarbeteibiologi, 10p
Biology Education Centre and Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala University
Supervisor: Fredrik Öberg, Ph.D.