McGill professor explores methods of gene expression
Biochemistry professor Josée Dostie of McGill University discussed her most recent discoveries in the regulation of human gene expression at a lecture last Tuesday at Dartmouth Medical School. Dostie described the ways in which the human genome is organized and which different elements of the genome communicate and interact with each other.
Dostie explained that human genome organization falls into three primary categories. Along the lengths of chromosomes, the genome is organized linearly and divided into functional genes and regulatory elements. In turn, these chromosomes are bound to proteins, forming a complex material called chromatin. Lastly, the chromatin itself is arranged spatially within the cellular nucleus.
Though the structure of genes and chromosomes has been well-documented over the past decade, the three-dimensional organization of the chromatin itself remains to be fully understood. Without question, this organization is essential for cell function. The collection of DNA within a human cell can be nearly two meters in length. Spatial organization is necessary so that the genetic code can be easily accessed for replication and repairs.
Dostie explained that although chromosomes occupy distinct territories within the nuclear space, an extensive degree of communication and interaction exists within and between chromosomes. One gene can activate another downstream or on a separate chromosome entirely.
At her McGill laboratory, Dostie and her research team have sought to analyze the physical chromatin contacts that occur in developing cells. These contacts can be “photographed” using a technique known as Chromosome Conformation Capture, or 3C.
In 3C, a fixed population of cells is mixed with a restriction enzyme that digests particular elements of DNA, followed by an enzyme called ligase. If two genes are proximal to each other, 3C can replicate these contacts for identification. Although 3C is the standard technique that has been used to describe many of the interactions within the genome, it is a labor-intensive process that cannot easily map large regions of the genome at once.
Dostie’s team recently developed an improvement known as 3C-Carbon Copyor 5C that has the potential to detect millions of chromatin contacts simultaneously.
Furthermore, Dostie has focused much of her attention on the description of human HOX genes. The proteins encoded by the HOX genes act as transcription factors and play an integral role in normal embryonic development. In adults, HOX genes are usually “silenced.” When they become active, HOX genes are believed to play a role in the development of cancer.
It is a long way from understanding the extent of these chromatin interactions. Nevertheless, through their continuous work, Dostie and her research team are closer than ever to understanding the specific mechanisms that promote the onset of cancer among normal adult cells.