THE TIGHT-SKIN MOUSE - DEMONSTRATION OF MUTANT FIBRILLIN-1 PRODUCTIONAND ASSEMBLY INTO ABNORMAL MICROFIBRILS

Mice carrying the Tight skin (Tsk) mutation harbor a genomic duplicati on within the fibrillin-1 (Fbn 1) gene that results in a larger than n ormal in-frame Fbn I transcript, In this study, the consequences of th e Tsk mutation for fibrillin-containing microfibrils have been examine d. Dermal fibroblasts from Tskl+ mice synthesized and secreted both no rmal fibrillin (similar to 330 kD) and the mutant oversized Tsk fibril lin-1 (similar to 450 kD) in comparable amounts, and Tsk fibrillin-1 w as stably incorporated into cell layers. Immunohistochemical and ultra structural analyses of normal and Tskl+ mouse skin highlighted differe nces in the gross organization and distribution of microfibrillar arra ys, Rotary shadowing of high M-r preparations from Tskl+ skin demonstr ated the presence of abundant beaded microfibrils. Some of these had n ormal morphology and periodicity, but others were distinguished by dif fuse interbeads, longer periodicity, and tendency to aggregate, The pr esence of a structurally abnormal population of microfibrils in Tsklskin was unequivocally demonstrated after calcium chelation and in den aturating conditions, Scanning transmission electron microscopy highli ghted the presence of more mass in Tskl+ skin microfibrils than in nor mal mice skin microfibrils, These data indicate that Tsk fibrillin-1 p olymerizes and becomes incorporated into a discrete population of bead ed microfibrils with altered molecular organization.