Widespread distribution of the major polypeptide component of MAP 1 (microtubule-associated protein 1) in the nervous system.

Abstract

We prepared a monoclonal antibody to microtubule-associated protein 1 (MAP 1), one of the two major high molecular weight MAP found in microtubules isolated from brain tissue . We found that MAP 1 can be resolved by SDS PAGE into three electrophoretic bands, which we have designated MAP ]A, MAP 113, and MAP 1 C in order of increasing electrophoretic mobility. Our antibody recognized exclusively MAP 1A, the most abundant and largest MAP 1 polypeptide . To determine the distribution of MAP 1A in nervous system tissues and cells, we examined tissue sections from rat brain and spinal cord, as well as primary cultures of newborn rat brain by immunofluorescence microscopy. Anti-MAP 1 A stained white matter and gray matter regions, while a polyclonal anti-MAP 2 antibody previously prepared in this laboratory stained only gray matter . This confirmed our earlier biochemical results, which indicated that MAP 1 is more uniformly distributed in brain tissue than MAP 2 (Vallee, R . B., 1982, /. Cell Biol., 92 :435-442) . To determine the identity of cells and cellular processes immunoreactive with anti-MAP 1A, we examined a variety of brain and spinal cord regions . Fibrous staining of white matter by anti-MAP 1A was generally observed . This was due in part to immunoreactivity of axons, as judged by examination of axonal fiber tracts in the cerebral cortex and of large myelinated axons in the spinal cord and in spinal nerve roots . Cells with the morphology of oligodendrocytes were brightly labeled in white matter . Intense staining of Purkinje cell dendrites in the cerebellar cortex and of the apical dendrites of pyramidal cells in the cerebral cortex was observed . By double-labeling with antibodies to MAP 1A and MAP 2, the presence of both MAP in identical dendrites and neuronal perikarya was found. In primary brain cell cultures anti-MAP 2 stained predominantly cells of neuronal morphology . In contrast, anti-MAP 1A stained nearly all cells . Included among these were neurons, oligodendrocytes and astrocytes as determined by double-labeling with anti-MAP 1A in combination with antibody to MAP 2, myelin basic protein or glial fibrillary acidic protein, respectively . These results indicate that in contrast to MAP 2, which is specifically enriched in dendrites and perikarya of neurons, MAP lA is widely distributed in the nervous sytem .Microtubules purified from a variety of sources have been shown to consist of both tubulin, the principal structural protein, and a diverse group of microtubule-associated proteins, or MAP (5,6,27,34,45,46). The MAP have been implicated in the regulation ofmicrotubule assembly (26,46), and. in mediating the interaction of microtubules with other structural elements ofthe cytoplasm (1,3,12,13,15,22,32,33,35). In brain, the most prominent MAP are high molecular weight proteins . These proteins have been divided into two classes, MAP 1 and MAP 2, on the basis oftheir electrophoretic mobility (34). MAP 2 (M, 270,000) remains soluble when microtubules are exposed to elevated temperatur...

Axonal transport of the cytoplasmic matrix.

“…The axonal transport studies indicate that MAP 1 and MAP 2 are present in much smaller amounts than the tau proteins in these axons. This is consistent with immunocytochemical studies that demonstrate that MAP 2 is much more abundant in dendrites than axons (7,42,62) .…”

The effect of amphetamine analogs on cleaved microtubule-associated protein-tau formation in the rat brain

“…However, additional studies are necessary to determine whether C-tau immunoreactivity in astrocytes results either from C-tau of neuronal origin that is scavenged by astrocytes, leading to its localization within these cells or from C-tau isoforms that always reside within astrocytes. Although tau is usually associated with the axons of neurons, tau has also been shown to be present in glial cells (Bloom et al, 1984, LoPresti et al, 1995, Yoshiyama et al, 2003. Tau accumulation in glia is the result of increased synthesis or reduced clearance of the molecule that results in tau fibrillization and degeneration of the affected cells (Yoshiyama et al, 2003).…”

High-Mr microtubule-associated proteins: properties and functions

“…The position of bands within a column is roughly as documented, but the standardization of electrophoretic mobilities among the columns is arbitrary because different gel systems were used. (a) PC 12 cells (Greene et al, 1983); (b) calf brain white matter (Bloom et al, 1984a) brain (Riederer & Matus, 1986). …”

“…Greene et al (1983) first referred to two MAP 1 components in pheochromocytoma (PC) 12 cells as MAP 1.1 and 1.2, in order of increased electrophoretic mobility. Bloom et al (1984a) designated three MAP 1 bands obtained after purification of microtubule proteins with taxol from calf corpus callosum as MAP IA, I B and 1C, again, in order of decreasing apparent Mr. The same terminology was used for three major MAP 1 components copurifying with microtubules assembled from hog brain (Herrmann et al, 1985) by the procedure of Karr et al (1979), which is based on temperature-dependent polymerization; a fourth, minor, component exhibiting an electrophoretic mobility slightly lower than that of MAP I A was called MAP lA'.…”

“…On the other hand, structural divergencies of these two MAP 1 species were revealed by silver-stained one-dimensional peptide maps and by several monoclonal antibodies that only react with one of the two (Bloom et al, 1985a (Herrmann et al, 1985), it is readily susceptible to proteolysis, and it represents a major substrate for endogenous kinases. None of these characteristics seems to apply to the protein referred to as MAP IC by Bloom et al (1984a), which was later identified as cytoplasmic dynein (see below). In line with this, a Ca2+-protease-resistant dynein variant isolated from mammalian brain in the authors's laboratory (Koszka et al, 1987) which is potentially homologous to the dynein variant identified by Vallee and Collins & Vallee, 1987).…”