Role of Chemokine Signaling and Heparin Binding Growth Factors During Ocular Neurovascular Patterning
Lwigale, Peter Y; Carson, Daniel
Doctor of Philosophy
The embryonic eye provides a unique context in which we can study the mechanisms of neurovascular patterning and wound healing. The anterior eye requires highly regulated signaling for the proper formation of an avascular, highly innervated, and transparent cornea. By studying ocular development in avian and murine models, we can begin to understand how signals in the embryo regulate interactions of the neural crest cells and ocular ectoderm for the proper formation of the anterior eye structures. The purpose of this work is to elucidate the functions of a chemokine (CXCL12), and two heparin-binding growth factors (midkine and pleiotrophin) during anterior eye development and neurovascular patterning. CXCL12 and its receptor CXCR4 are required for the proper vascular patterning in other organ systems, but their functions in the eye have yet to be discovered. Here I demonstrate that CXCL12-CXCR4 signaling has two major functions during ocular development: first, CXCL12 expression in the trigeminal placode is required for the proper formation of the trigeminal ganglion; second, CXCL12 expression in the periocular neural crest is required for proper vascular remodeling during later ocular development. Disruption of CXCL12 signaling in either the placode or neural crest result in significant neurovascular defects of the anterior eye. Midkine (MDK) and pleiotrophin (PTN) are two secreted proteins which make up their own family of heparin-binding growth factors. MDK expression can be induced by retinoic acid, which is an important signal for general ocular development. Here I report MDK and PTN expression during corneal and retinal development. Both MDK and PTN were expressed in the migrating neural crest, but otherwise had generally complimentary expression patterns. Although MDK and PTN were conserved in the anterior eye between chick and mouse, they had differential expression during retinal development. I also demonstrate that MDK and PTN in the anterior eye may signal to trigeminal nerves through ITGB1 and RPTPZ. Lastly, I present a novel method to study embryonic wound healing in culture. The embryonic cornea possesses regenerative properties not found in the adult, and can maintain its transparency by healing nonfibrotically. However, current methods of studying embryonic wound healing are limited in its efficiency and adaptability. Here I provide a protocol to study mechanisms of wound healing in an ex vivo model that allows for higher throughput, reproducibility, and adaptability. The results presented in this document give a glimpse of the intricate and highly regulated signaling required during ocular development. Better understanding of the molecular mechanisms are required for the creation of better therapeutics for ocular neurovascular diseases and wound healing.
Development; cornea; neural patterning; vascular patterning