Microtubule-associated protein 2 also known as MAP2 (theoretical molecular weight 199 kDa) belongs to the MAP2/Tau family which in addition to the two neuronal forms MAP2 and Tau also includes MAP4 (1). For MAP2, four different isoforms have been identified which are produced through alternative splicing including MAP2a, MAP2b, MAP2c and MAP2d (1). MAP2 isoforms contain multiple microtubule-binding domains located near the carboxy terminal, a variably sized amino-terminal projection domain, and a conserved protein kinase A binding domain. MAP2c and MAP2d isoforms have a shorter amino-terminal projection domain, lower molecular weight and are identifiable at ~70 kDa in SDS-PAGE analysis (2,3). MAP2's carboxy terminal domain supports interactions with microtubules, actin, and intermediate filaments (2).
MAP2 isoforms are developmentally regulated and differentially expressed in neurons and some glia. MAP2c is predominantly expressed in the developing brain while the other isoforms are expressed in the adult brain. The distribution of MAP2 isoforms also varies, with MAP2a and MAP2b predominantly localized to dendrites, while MAP2c is also found in axons. Lastly, the expression of MAP2d is not limited to neurons and may be found in glia, specifically oligodendrocytes (1, 2). MAP2 isoforms associate with microtubules and mediate their interaction with actin filaments thereby playing a critical role in organizing the microtubule-actin network. In neurons, MAP2 isoforms are implicated in different processes including neurite initiation, elongation and stabilization as well as axon and dendrite formation (2). Knockout of MAP expression in animal models results in a variety of functional and structural brain defects according to the isoform affected (e.g., reduced LTP and LTD, reduced myelination, absence of corpus collosum, motor system malfunction, abnormal hippocampal dendritic morphology, abnormal synaptic plasticity) (4).
1. Dehmelt, L., & Halpain, S. (2005). The MAP2/Tau family of microtubule-associated proteins. Genome Biology. https://doi.org/10.1186/gb-2004-6-1-204
2. Mohan, R., & John, A. (2015). Microtubule-associated proteins as direct crosslinkers of actin filaments and microtubules. IUBMB Life. https://doi.org/10.1002/iub.1384
3. Shafit-Zagardo, B., & Kalcheva, N. (1998). Making sense of the multiple MAP-2 transcripts and their role in the neuron. Molecular Neurobiology. https://doi.org/10.1007/BF02740642
4. Tortosa, E., Kapitein, L. C., & Hoogenraad, C. C. (2016). Microtubule organization and microtubule-associated proteins (MAPs). In Dendrites: Development and Disease. https://doi.org/10.1007/978-4-431-56050-0_3