Although Arf is broadly known as a tumor suppressor gene, it also is essential for mouse eye development. Work from my laboratory has demonstrated that mice lacking Arf are born blind with a severe developmental eye disease, mimicking a human eye disease known as Persistent Hyperplastic Primary Vitreous (PHPV). This eye disease is due to failed involution of the hyaloid vasculature that provides nutrients to the developing eye. One of my overall goals is to elucidate the fundamental mechanisms by which the Arf gene product guides these critical vascular changes during normal eye development. Very little is known about basic mechanisms that control Arf transcription or the expression of its gene product, p19Arf. But, discoveries from my laboratory team over the last 21/2 years have provided new information challenging the existing dogma that Arf is primarily controlled by abnormal or excessive proliferation signals. Instead, we showed that an important signaling protein - Transforming Growth Factor -2 (Tgf2) - controls Arf expression during eye development. As importantly, Arf is absolutely essential for Tgf2 to guide normal eye development. With these two findings, we established a new biochemical and genetic pathway that is essential for normal eye development and vision. Building naturally from our findings over the last 2 1/2 years, I intend to close three critical gaps in my understanding of how Tgf2 can induce Arf expression: What are the DNA elements that flank the Arf gene to enhance its expression when stimulated by Tgf2? How does Tgf engage RNA polymerase II at the Arf promoter and how is this polymerase controlled once it is poised? How do the Tgf dependent enhancers and trans-activating factors intersect with the transcriptional machinery to increase Arf expression? Studying this pathway from Tgf2 to p19Arf will deepen our understanding of how the two proteins operate in the developing eye. It will also inform our knowledge of the broader role that Tgf and p19Arf may play in perivascular cells that obviously have the capacity to either stabilize or destabilize underlying blood vessels. In the end, fully characterizing these molecular processes - including identifying the key regulatory elements in the gene and essential cofactors - will allow me to more effectively carry out genetics studies of patients with PHPV or similar eye diseases. From a broader perspective, though, the knowledge may also illustrate how Arf might be controlled in cancer and how Tgfs may carry out other functions in development and disease.
The Arf gene plays an essential role to prevent primary vitreous hyperplasia (PHPV) and to drive hyaloid vascular regression - two processes that are essential for normal vision. I previously showed that the temporally- and spatially-restricted expression of the Arf gene product depends on signals from the Transforming Growth Factor beta 2 (Tgf2) and that Arf is essential to the role that Tgf2 plays promoting eye development. Research that I will conduct in the continuation of this project will define, at a molecular level, the steps needed for Tgf2 to augment Arf expression in this newly-discovered biochemical pathway that is essential for normal vision.
