During development the epidermis protects the embryo from chemical, biological and mechanical stresses. This organ is also essential in providing tension, necessary for shaping organs while also allowing for cell shape changes necessary for morphogenesis. The integrity of the epidermis is mediated by intercellular junctional complexes, including desmosomes. However, relatively little is known about how desmosomes are regulated during embryonic development. My lab has uncovered a potentially new role for c-Jun NH(2)- terminal kinase (JNK) signaling in regulating desmosomal proteins in the epidermis of Xenopus laevis tadpoles. JNK signaling has been shown to regulate transcription of a variety of genes or to directly phosphorylate cytoskeletal proteins during embryogenesis. But, this MAP kinase family member has never been shown to regulate desmosomal function. We have found that decreased JNK signaling results phenotypes consistent with human conditions resulting from defective desmosomal function such as epidermal fragility and bubbling as well as heart and craniofacial defects. Further, in a proteomics screen for JNK targets we uncovered two plakins;epiplakin and periplakin that are associated with desmosomes in mammals. This proposal aims to use a combination of methods to perform temporal and spatial loss of function of JNK signaling in the epidermis. This will be followed by characterizing the effects in the whole embryo and at the cellular level. We will perform epidermal specific loss of JNK1 function using antisense technology, photoactivation and transplant assays. Desmosomes will be analyzed by electron and confocal microscopy. Finally we aim to determine whether JNK regulates the desmosomal proteins, epiplakin and periplakin, indirectly via transcription or by direct phosphorylation using quantitative PCR and co-immunoprecipitations. I believe this to be an innovative grant that uses whole embryo approaches and bridges developmental signaling and desmosomal function.
The broad goals of this proposal are to investigate how the desmosome is regulated during epidermal development. This work, therefore, has the potential to contribute to our understanding of human skin disorders which result from defects in desmosomal function.