Transient expression of an intermediate filament-associated protein (IFAPa-400) during in vivo and in vitro differentiation of chick embryonic cells derived from neuroectoderm.

The expression of an intermediate filament (IF) associated protein (IFAPa-400) and IF proteins was investigated during chick neurogenesis. Using immunoblots and indirect immunofluorescence we have found that IFAPa-400 was strongly expressed during the early events of nervous tissue ontogenesis and disappeared thereafter. IFAPa-400 was elevated in the brain and retina until ED 10 and until hatching in the cerebellum. This protein was shown to be transiently expressed in the Müller glia of the developing retina. In the brain, IFAPa-400 decreased as development proceeded in a way similar to vimentin but the latter remained elevated in the retina and the cerebellum radial glia (Müller and Bergmann cells). In all tissues examined, GFAP was detected long after the disappearance of IFAPa-400. In dorsal root ganglion cell cultures, IFAPa-400 and vimentin were absent from mature neurons but were coexpressed into supportive cells. In trunk neural crest cell cultures, IFAPa-400 and vimentin were present in all cells after one day but IFAPa-400 became undetectable after a few days of culture in differentiated melanocytes and catecholaminergic neurons. The transient expression of this giant cytoskeletal protein in non-differentiated cells deriving from the neuroectoderm could reflect a structural change which precedes overt cytodifferentiation.