Sensory axon guidance molecules in avian skin

The goal of this dissertation research was to identify and begin to characterize the contribution of two classes of molecules, chondroitin sulfate proteoglycans (CSPGs) and neurotrophins (NTs) in patterning the innervation of avian skin. In particular, we investigate the role of these molecules in restricting axons to dermis in avian skin. The work described in Chapter 2 demonstrates that, while CSPGs contribute to the avoidance of chick epidermis by cutaneous sensory neurites, they are clearly not solely responsible. Chapter 3 details the possible inhibitory contribution of a member of an additional class of molecules, the neurotrophins (NTs), involved in patterning and maintaining sensory innervation. Our data implicate BDNF as an inhibitory component of chick epidermis that prevents sensory neurites from invading it. Neuronal development, which includes pathfinding, target selection and ramification with the correct target, is complex. Here we have utilized a system that allowed us to tease out at least part of the complex picture. By studying avian cutaneous innervation, we have proposed a model with multifactorial control or two classes of inhibitory guidance molecules (CSPGs and NTs) in this system. Using this more simplified system, it has become more increasingly clear how complex the scenario is-even at this level.