Answers to some questions in science require the development of new technologies; molecular biologists once examined selected pieces of DNA and the proteins that bound them, but advances in computation and instrumentation mean biologists can now determine where proteins bind across the whole genome, and look at expression of all the genes in a cell in one experiment.

Professor Jennifer Mitchell of U of T’s Department of Cell & Systems Biology is now revisiting her PhD work on how the transition from pregnancy to labour occurs  by using these new techniques. During pregnancy the uterus is not able to contract synchronously, but just before labour the muscle layer of the uterus changes so that it can produce the coordinated contractions required for birth. Mitchell’s PhD work studied control of a “gap-junction” protein that allows cell-to-cell communication. She examined a class of proteins designated AP-1 that regulate the amount of gap junction alpha 1 (GJA1) protein in the myometrium, the muscle layer of the uterus.

During labour, cells in the myometrium transition from a dormant to a contractile (pushing) state. Expression of the Gja1 gene is associated with this transition, and Mitchell identified AP-1 proteins that could cause the expression of Gja1 just before the onset of labour. Although she determined certain AP-1 proteins could turn on Gja1, the technology of the time couldn’t evaluate the role of these proteins on a genome-wide scale.

In collaboration with Temerty Faculty of Medicine Professor Oksana Shynlova of the Lunenfeld-Tanenbaum Institute, Mitchell and her two graduate students, Virlana Shchuka and Luís Abatti, developed high-throughput techniques to analyze protein binding to DNA and assess RNA expression across the whole genome at different phases of pregnancy. They examined not just Gja1, but all the genes turned on or off at multiple time points during gestation in mice.

By analyzing the proteins associated with DNA around these genes, Mitchell’s team identified epigenetic modifications in mouse myometrium. Epigenetic modifications change the way the DNA is packaged at specific regions, and Mitchell’s observed modifications permit binding of AP-1 proteins. The results of this research have been published in the peer-reviewed journal PLOS Biology: “The pregnant myometrium is epigenetically activated at contractility-driving gene loci prior to the onset of labor in mice”.

One remaining mystery is that the observed epigenetic changes occur four days prior to the onset of labour, so there must be a further signal that turns on contractile genes. It is likely that premature gene expression leading to early myometrial contractions and preterm labor in humans is the result of this signal occurring too early. Mitchell and Shynlova’s teams have recently received funding from the Canadian Institutes for Health Research to delve deeper into this mystery with the goal of identifying genes and protein targets for drugs to prevent preterm labor in humans.