MAP-0, A 400-KDA MICROTUBULE-ASSOCIATED PROTEIN UNIQUE TO TELEOST FISH

Microtubules from neural tissues of the Atlantic cod, Gadus morhua, an d of several species of Antarctic teleosts are composed of tubulin and several microtubule-associated proteins (MAPs), one of which has an a pparent molecular weight of similar to 400-430 kDa. Because its appare nt molecular weight exceeds those of the MAP 1 proteins, we designate this high molecular weight teleost protein MAP 0. Cod MAP 0 failed to cross-react with antibodies specific for MAPs 1A, 1B and 2 of mammalia n brain, for MAP H1 of squid optic lobe, and fur chicken erythrocyte s yncolin, which suggests that it has a novel structure. Similarly, MAP 0 from the Antarctic fish was not recognized by an antibody specific f or bovine MAP 2. Together, these observations suggest that MAP 0 is a novel MAP that may be unique to fish. To determine the tissue specific ity and phylogenetic distribution of:this protein, we generated a rabb it polyclonal antibody against cod MAP 0. Using this antibody, we foun d that MAP 0 was present in microtubule proteins isolated from cod bra in tissues and spinal cord but was absent in microtubules from heart, liver, and spleen. At the subcellular level. MAP 0 was distributed in cod brain cells in a punctate pattern coincident with microtubules but was absent in skin cells. MAP 0 was also detected in cells of the per ipheral nervous system. A survey of microtubule proteins from chordate s and invertebrates showed that anti-MAP 0-reactive homologs were pres ent in five teleost species but not in more primitive fish and inverte brates or in higher vertebrates. MAP 0 bound to cod microtubules by io nic interaction at a site recognized competitively by bovine MAP 2. Al though its function is unknown, MAF 0 does not share the microtubule-b inding properties of the motor proteins kinesin and dynein. We propose that MAP 0 is a unique, teleost-specific MAP. (C) 1997 Wiley-Liss, In c.