The final form of the adult skull is achieved through a complex series of morphogenetic events and growth, largely during post-embryonic development. Many common human congenital defects in the skull have their foundation in these developmental events. The treatment options in human patients are far from perfect, and improvements demand a more complete understanding of the biology underlying post-embryonic skull formation. However, by their complex development and relatively late occurrence, these clinically relevant stages in skull development have been less accessible in experimental organisms. The zebrafish displays fundamental similarity in skeletogenesis to mammals, including in formation of the vault of the skull and the cranial sutures. Although the later events of skull and suture formation have been relatively less well studied in zebrafish, they are nonetheless accessible for manipulations and imaging, making the zebrafish an ideal system to further our understanding of these complex events. Through a set of interconnected Aims, we propose to establish and make available to the community tools that will lay the foundation for the use of zebrafish to examine skull and suture formation. We will first construct an online, interactive atlas of normal skull development, encompassing the stages during which the vault of the skull is forming. The foundation of the atlas will be images generated by high-resolution computed tomography (micro-CT), which will be annotated and available for download. These will be complemented by images of transgenic zebrafish expressing fluorophores in critical cell populations, such as chondrocytes and osteoblasts at different stages of development. For the transgenics, we will optimize recently developed methods for fixation and clearing of large (>1 mM) tissue samples and use a versatile zoom macro-confocal scope. This approach will allow creation of lower resolution data sets from which we can generate three-dimensional reconstructions of gene expression in an entire skull, and will also allow high resolution imaging of specific structures. The transgenic lines used for the imaging studies will also serve as the basis for a transgenic system, using phiC31 recombinase, to allow replacement of the transgene coding sequences in genomic context while preserving tissue-specific expression patterns; the reagents (fish lines and plasmids) will available to the community. Finally, both of the laboratories in this application are engaged in ongoing genetic screens to identify mutations causing defects in the juvenile or adult skull. Using a select set of mutants with clinically relevant phenotypes, we will apply the imaging approaches above to describe the defects in morphology and gene expression during skull development. Through the combined generation of a comprehensive atlas and a set of transgenic and genetic tools, we will substantially advance the use of zebrafish in the study of skull development, and greatly facilitate comparative studies with mammals that will advance treatment options in human patients.
Human birth defects affecting the skull are common, and have devastating clinical consequences. Our proposed experiments are designed to reveal the biological mechanisms underlying abnormal skull development, using the zebrafish as a model organism. Through analysis of this tractable model organism, we will create a publically available database of normal events in skull development, and how they change in abnormal development, which will facilitate comparisons with other model organisms, such as mouse, and shed light on human disease mechanisms.
