Although Arf is broadly known as a tumor suppressor gene, it also is essential for mouse eye development. Mice lacking Arf are born blind with a severe developmental eye disease, mimicking a human eye disease known as Persistent Hyperplastic Primary Vitreous. Very little is known about basic mechanisms that control Arf transcription or the expression of its gene product, p19Arf. One of my overall goals is to use elucidate the fundamental mechanisms driving the expression of this important gene. The existing dogma holds that Arf functions as an """"""""oncogene sensor"""""""" such that its expression is induced in cells carrying abnormal or excessive proliferation signals from oncogene activation. Mechanisms by which an individual cell can discriminate between an oncogenic stimulus and an equally intense, normal proliferation signal - such as that occurring during development - are not at all clear. Recently, though, members of my laboratory and I made a surprising discovering challenging the current paradigm. Specifically, while exploring mechanisms by which p19Arf prevented primary vitreous hyperplasia in the developing mouse, we showed that its promoter is activated in an exquisitely controlled pattern during mouse development. This finding allows me to safely conclude that Arf control must extend beyond the cell intrinsic signals provided by oncogene activation. Working from our new findings that part of the Tgf22 -/- phenotype resembles that in the absence of Arf, I have established the Transforming Growth Factor 2-2 (Tgf22) as an essential regulator of p19Arf and that the latter is required for the anti-mitogenic effects of Tgf22 in vivo and in vitro. In this proposal, I will take advantage of existing mouse and cell culture models to close three critical gaps in my knowledge: Does Tgf2 directly control p19Arf expression during eye development? What are the essential intracellular signals emanating from Tgf22? What are the fundamental mechanisms acting at the Arf promoter? Studying this pathway from Tgf22 to p19Arf will deepen our understanding of how the two proteins operate in the developing eye, and better define the genetic abnormalities that can contribute to human diseases characterized by hyperplasia in the vitreous. From a broader perspective, though, this potentially sheds new light on how Arf may be controlled in cancer cells and how Tgf2s may carry out other functions during development.
The Arf gene plays an essential role to prevent primary vitreous hyperplasia and hyaloid vascular regression, processes that are critical for normal vision. We have previously defined its temporally- and spatially-restricted expression in the developing eye, but the mechanisms underlying this expression pattern are totally unknown. My Preliminary Studies in this proposal provide the first insight: Tgf22 plays a key role in the process. Experiments in this proposal define will define the cellular and molecular mechanisms by which Tgf22 accomplishes this.
