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 b-2 (Tgfb2) - controls Arf expression during eye development. As importantly, Arf is absolutely essential for Tgfb2 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 Tgfb2 can induce Arf expression: What are the DNA elements that flank the Arf gene to enhance its expression when stimulated by Tgfb2? How does Tgfb engage RNA polymerase II at the Arf promoter and how is this polymerase controlled once it is poised? How do the Tgfb dependent enhancers and trans-activating factors intersect with the transcriptional machinery to increase Arf expression? Studying this pathway from Tgfb2 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 Tgfb 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 Tgfbs 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 (Tgfb2) and that Arf is essential to the role that Tgfb2 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 Tgfb2 to augment Arf expression in this newly-discovered biochemical pathway that is essential for normal vision.
|Iqbal, Nida S; Xu, Lin; Devitt, Caitlin C et al. (2014) Isolation and characterization of mammalian cells expressing the Arf promoter during eye development. Biotechniques 56:239-49|
|Iqbal, Nida; Mei, Jie; Liu, Jing et al. (2014) miR-34a is essential for p19(Arf)-driven cell cycle arrest. Cell Cycle 13:792-800|
|Mary-Sinclair, Michelle N; Wang, Xiaofei; Swanson, Douglas J et al. (2014) Varied manifestations of persistent hyperplastic primary vitreous with graded somatic mosaic deletion of a single gene. Mol Vis 20:215-30|
|Zheng, Yanbin; Devitt, Caitlin; Liu, Jing et al. (2013) A distant, cis-acting enhancer drives induction of Arf by Tgf* in the developing eye. Dev Biol 380:49-57|
|Zheng, Yanbin; Devitt, Caitlin; Liu, Jing et al. (2013) Arf induction by Tgf* is influenced by Sp1 and C/ebp* in opposing directions. PLoS One 8:e70371|
|Zheng, Yanbin; Zhao, Yi D; Gibbons, Melissa et al. (2010) Tgfbeta signaling directly induces Arf promoter remodeling by a mechanism involving Smads 2/3 and p38 MAPK. J Biol Chem 285:35654-64|