ON THE RELATIONSHIP OF BRAIN FILAMENTS TO MICROTUBULES¹

Abstract

A method has been developed for the isolation of a previously undescribed fibrous protein from rat brain. The newly isolated material consists of bundles of tightly packed 70-80 8, diameter filaments. Based on studies employing degenerated rat optic nerve, it is proposed that these filaments correspond to the well-described astrocyte filaments observed in sectioned preparations of mammalian brain. The purified filaments are stable over a wide temperature range, are not disrupted by colchicine, and exhibit limited solubility in the absence of denaturants or detergents. In neutral SDS-polyacrylamide gel electrophoresis, the filament protein runs as a single band with an apparent molecular weight of 57,000 daltons. This preparation also migrates as a single band in alkaline urea gels, and as a well-resolved doublet on discontinuous SDS-urea gels. In all three electrophoretic systems, the filament subunits co-migrate with rat brain tubulin. Comparative peptide maps of the filament subunits and tubulin indicate a large degree of homology. Our results suggest that microtubules and astrocyte filaments are composed of the same or very similar protein subunits.

Isolation and characterization of glial filaments from human brain.

“…In particular, it did not split into two components during electrophoresis under conditions in which the o~-and/3-monomers of tubulin are resolved. Such splitting has previously been reported for presumptive glial filament protein (21).…”

Protein differences associated with the loss of myelinated axons and fibrillary gliosis in rat optic nerves following Wallerian degeneration

“…This could be interpreted as indicating that nerve and glial fibers are similar in polypeptide composition. According to Johnson and Sinex [9] neurotubules and astroglial filaments are composed of the same or very similar protein subunits, that is tubulin. A more likely explanation may reside in the fact that the protein subunits of two major fibrillary structures of the brain, that is neurofilaments and glial filaments, although chemically different have similar molecular weight and thus may be difficult to separate on SDS-gel electrophoresis.…”

The structure of postsynaptic densities isolated from dog cerebral cortex: II. characterization and arrangement of some of the major proteins within the structure

“…These filaments, wider in diameter than the microfilaments, some of which are undoubtedly composed of actin-like protein, have been reported to contain a major protein with assigned molecular weights of 60,000 (57), 57,000 (30), 54,000 (9), 51,000 (10), and 50,000 (29). Although some of these filament preparations are reported to originate from glial cells (9,30), the morphology of our filaments ( Fig. 12) most closely resembles that of the one isolated from axons (10).…”