Loop arrays in mouse brain demonstrated with antisera to cytokeratins and monoclonal antibodies to several classes of intermediate filaments: strain differences and developmental expression.

Some monoclonal antibodies raised against mouse brain antigens display a novel loop array apparently localized within the cytoplasm of neurons in fresh frozen sections of adult mouse brain. By indirect immunofluorescence, these loops are detectable in the cerebral cortex, thalamus, brainstem, and are particularly striking in association with pyramidal neurons of the hippocampus. The loops are also seen with polyclonal antibodies to the cytokeratin class of intermediate filaments. The antibodies which react with these loops also react with ependymal cells. Western blot analysis of crude insoluble cytoskeletal components of mouse brain with antibodies of cytokeratins confirm the presence of reactive bands in the range of 40-60 kdalton, appropriate in molecular weight for this class of cytoskeletal filaments. This evidence suggests that the loops share antigenic determinants with non-neural cytokeratins. During development, immunoreactive structures are first seen as small punctate or curvilinear profiles, which change into a loop array at approximately 14 days postnatal age in several mouse strains. However, in 8 of 15 different mouse strains, these immature punctate profiles remain without morphological alteration to loops throughout adult age. The F1 crosses between strains with and without the loops develop loops, but on average they are of smaller size than in the positive parent.