Expression of microtubule-associated proteins MAP2 and tau in cultured rat brain oligodendrocytes

Abstract

Oligodendrocytes in culture are characterized by large membranous sheets containing an elaborate network of microtubules. Microtubule-associated proteins (MAPs) participate in microtubule stability and the regulation of the cellular architecture. We have investigated the expression of two major groups of MAPs, MAP2 and tau, in cultured rat brain oligodendrocytes. Alternatively spliced isoforms of mRNAs encoding MAP2 and tau were assessed by means of reverse transcription and polymerase chain reaction using a newly designed set of MAP2- and tau-specific primers. The data were compared with data obtained with cultures of rat brain astrocytes and rat cerebral neurons, and adult rat brain. The results show that oligodendrocytes, similarly to neurons, express mainly MAP2c transcripts containing three microtubule-binding repeats. They also contain small amounts of MAP2b mRNA. Six low molecular weight tau isoforms, namely tau 1-6, have been described in the brain (Goedert et al. 1991). The major isoform of tau mRNA in oligodendrocytes was found to be tau 1, which represents a marker typical for immature neurons. Tau 2 and tau 4 isoforms were also detected, albeit at a very low level. Immunoblot analysis of oligodendroglia cell extracts confirmed the presence of tau protein. It migrates as a single polypeptide with an apparent molecular weight of approximately 55 kDa. In addition, oligodendrocytes express MAP2c protein, which migrates as a close double band with an apparent molecular weight around 70 kDa. Indirect immunofluorescence staining indicated that tau and MAP2 immunoreactivity was expressed in oligodendrocytes of immature and mature morphologies in the cell somata and cellular processes. Tau was particularly found in the end of the cellular extensions, and both proteins exhibited a distribution similar to myelin basic protein. Thus, oligodendroglia, like neuronal cells, contain microtubule-associated proteins, mainly MAP2c and the tau 1 isoform, although at a much lower level. The presence of these MAPs in myelin-forming cells further points to the functional significance of the cytoskeleton during oligodendrocyte differentiation, process outgrowth, and myelin formation.

Protein aggregate formation in oligodendrocytes: tau and the cytoskeleton at the intersection of neuroprotection and neurodegeneration

“…It has been implied that in adult rodent brain only 4R-tau isoforms are expressed. However, our data demonstrated that in rat brain 3R-tau isoforms are present yet at a much lower level (Müller et al, 1997;Gorath et al, 2001), which was later corroborated by Hanes et al (2009). In cultured oligodendrocytes tau protein is developmentally regulated and 4R-isoforms become more prominent, while 3R-isoforms decrease (Seiberlich et al, 2015).…”

“…A number of myelin specific proteins have been found to bind to MTs and specifically MBP, which is absolutely required for the formation of intact myelin, has been reported to function as a MT stabilizing protein in differentiated oligodendrocytes (Galiano et al, 2006;Richter-Landsberg, 2013). Furthermore a variety of MAPs, including high molecular weight MAPs and tau seem to be involved in the regulation of MT growth and stability (Müller et al, 1997;Richter-Landsberg, 2008).…”

“…until it was demonstrated to also be an oligodendroglial constituent (LoPresti et al, 1995;Müller et al, 1997).…”

Absence of Tau triggers age‐dependent sciatic nerve morphofunctional deficits and motor impairment

“…In line with previous studies demonstrating an absence of axonal deficits in neurons of Tau−/− animals (Yuan et al ., 2008; Vossel et al ., 2010), there were no differences in mRNA levels of transcription factors that critically regulate myelination process and/or maintenance, for example, Krox20 and Oct6 (data not shown), suggesting no gross changes in myelin gene regulation of Tau−/− Schwann cells. Furthermore, supporting the involvement of Tau and other cytoskeletal elements in myelination process, previous evidence suggests that Tau strongly colocalizes with MBP in distal tips of oligodendrocytes (LoPresti et al ., 1995; Muller et al ., 1997), suggesting that transportation and/or local MBP translation may require microtubule cytoskeleton and might be controlled by Tau–Fyn interaction (Klein et al ., 2002). As recent evidence suggests that Tau is responsible to locate Fyn in spines and Fyn has a well‐described role in myelination of both CNS and PNS (Kramer‐Albers & White, 2011), the above Tau–Fyn–MBP complex could be disrupted in the absence of Tau protein, affecting myelination signaling and process.…”

Expression of tau mRNA and soluble tau isoforms in affected and non‐affected brain areas in Alzheimer's disease

“…Since glial cells are largely the most abundant cell population in the white matter, it is probable that this PCR product results from the amplification of mRNAs present in astrocytes and/or oligodendrocytes. Rodent oligodendrocytes have been reported to express tau proteins [25] and cultured rat oligodendrocytes express both 3R and 4R tau mRNA [26]. Cultured astrocytes [27] and astrocytes in situ [28] express tau proteins.…”