Development of corneal structure and function is the result of the integration of multiple regulatory pathways converging to produce and maintain a transparent corneal stroma. The overall goals of this application are to elucidate the mechanisms regulating the sequential steps in corneal stroma-specific matrix assembly. A definition of the regulatory steps essential for normal development, growth and maturation provides a foundation for understanding stromal development as well as stromal repair versus regeneration and the potential modulation of these processes. Finally, these studies will address the molecular basis of corneal pathologies, such as cornea plana, corneal stromal congenital dystrophy, and stromal involvement in connective tissue disorders such as Ehlers Danlos Syndrome. Our overall hypothesis is that corneal matrix assembly involves a sequence of events with specific regulatory interactions at each step. The specific aims of this application are to: (Aim 1) elucidate the regulatory role(s) of collagen V in fibril assembly, protofibril structure and organization within the developing stroma; (Aim 2) determine the role(s) of the fibril-associated (FACIT) collagens XII and XIV in mediating protofibril organization and lamellae assembly in the developing stroma; and (Aim 3) determine the coordinate roles of small leucine-rich proteoglycans (SLRPs) in regulation of corneal fibril growth and packing and elucidate the dysfunctional regulation of matrix assembly in a mouse model of human corneal stroma congenital dystrophy. The aims are developed around the following hypotheses: (Aim 1) Nucleation of corneal fibril assembly is regulated by collagen V and this regulation is dependent on developmental stage-specific collagen V isoforms. In addition, collagen V interactions are linked to the keratocyte surface allowing cellular control of fibril organization. (Aim 2) Stromal compaction, packing of of protofibrils and assembly into developing lamellae are regulated by collagens XII and XIV through their association with the stromal fibrils. This developmental regulation involves a coordinate interaction between collagens XII and XIV. (Aim 3) Regulation of fibril growth steps and fibril organization involves synergistic regulation by different classes of SLRPs. In addition, the clinical phenotype in human corneal stromal congenital dystrophy is the result of a gain of function mutation involving the C-terminus of the decorin core protein. Mouse models deficient in specific matrix molecules will be utilized to analyze stromal development using biochemical, immunochemical, molecular, morphological and functional approaches. Definition of the regulatory steps in corneal-specific matrix assembly provides the foundation to further our understanding of corneal repair/regeneration, pathobiologies and the manipulation of these processes.