EFFECTS OF INTERMEDIATE FILAMENT DISRUPTION ON THE EARLY DEVELOPMENT OF THE PERIPHERAL NERVOUS-SYSTEM OF XENOPUS-LAEVIS

The principal function of intermediate filaments is to strengthen cell s. Their developmentally regulated, tissue-specific patterns of expres sion further suggest that they modulate cellular structural properties during development. To explore the role of intermediate filaments in development, we injected RNA encoding a truncated form of the Xenopus laevis middle-molecular-weight neurofilament protein (NF-M) into embry onic frog blastomeres at the 2-cell stage. A similar truncated form of mammalian NF-M disrupts neurofilaments (Type IV) and vimentin (Type I II) intermediate filaments in transfected fibroblasts. In cultures mad e from dissociated neural tubes and their adjacent myotomes, the resul tant protein disrupted both desmin filaments in muscle cells and neuro filaments in neurons during the first day of culture, which correspond s to stage 35/36 in the intact embryo. We next examined the effects of this truncated neurofilament protein on development of the nervous sy stem. The greatest effects were seen on development of cranial and pri mary motor nerves, which were severely stunted as late as stage 37/38. In addition to these effects, ectopic neurons also appeared immediate ly beneath the epidermis along the flank of tadpoles expressing the tr uncated neurofilament protein. Whereas the former effects on periphera l nerve development were nearly identical to effects obtained with inj ected neurofilament antibodies, the ectopic neurons were novel, sugges ting they resulted from the disruption of intermediate filaments other than the neurofilaments. These experiments thus implicate intermediat e filaments in several functions important for normal neural developme nt. (C) 1996 Academic Press, Inc.