The phosphorylated isoform of microtubule associated protein 1B (MAP1B) is expressed in the visual system of the tench (Tinca tinca, L) during optic nerve regeneration E. Vecino a, *, L. Ulloa b , J. Avila b a Departamento de Biologı ´ a Celular y Ciencias Morfolo ´ gicas, Facultad de Medicina, Universidad del Paı ´ s Vasco, 48940 Leioa, Vizcaya, Spain b Centro de Biologia Molecular Severo Ochoa, Facultad de Ciencias, Universidad Auto ´ noma de Madrid, 28049 Madrid, Spain Received 4 February 1998; received in revised form 20 February 1998; accepted 20 February 1998 Abstract By using Western blot analysis and immunohistochemistry we have demonstrated that microtubule associated protein 1B (MAP1B)-phos is present in growing and regenerating axons of retinal ganglion cells of fish (Tinca tinca, L). We have found that the levels of MAP1B-phos substantially increase in regenerating optic nerves. Our observations suggest that MAP1B-phos plays an important role in regeneration processes in the central nervous system (CNS) of the fish. These results are compared in the present paper with that found in the regenerating peripheral nervous system (PNS) of mammals.  1998 Elsevier Science Ireland Ltd. Keywords: Fish; Central nervous system; Microtubule associated protein; Optic nerve; Phosphorylation; Regeneration; Retina The axons of the retinal ganglion cells of a fish can regen- erate after optic nerve damage and re-establish their appro- priate pattern of synaptic connections in the optic tectum [12] thus mediating the recovery of visual function. This regeneration is a unique property of the visual system of the fish and it is not observed in mammals. The regenerating retinal ganglion cells of the fish have been extensively stu- died (for review see [5]). One of the changes in regenerating cells is a rapid increase of virtually all the major classes of axonally transported proteins, including cytoskeletal ele- ments such as tubulin and actin [5]. The mechanisms which underlie the regeneration are not fully understood but they may involve rearrangement and polymerization of microtubules [7]. Stable microtubules are a necessity of this process. Since microtubule associated proteins (MAPs) are necessary for the stability and arrangement of microtu- bules and facilitate the crosslinking of microtubules with other cytoplasmic components [9], it is likely that they are also involved in regeneration. The aim of the present work has been to study the expression of MAPs during the regen- eration of the optic nerve of the fish. We have focused our studies on MAP1B (also referred to as MAP5, MAP1.2 or MAP1.X) since this is the first MAP that is expressed in neurons during development [13]. MAP1B in its phosphory- lated form [4,16] is required for extension of neurites and it likely plays an important role in the plasticity of the neural cytoskeleton and in the regulation and organization of the neural cytoskeleton during the outgrowth and regeneration of neurites [2,8]. Moreover, MAP1B has been found in the central nervous system (CNS), particularly in the retina of mammals, birds and amphibians [10,14,15,20]. However, no experiments have been made to study the expression of MAP1B-phos in vivo during the regeneration of the CNS. Most of the in vivo studies have been done during the regeneration of the peripheral nervous system (PNS) using the sciatic nerve as a model [2]. Since the retina of the teleost grows continually throughout life and the optic nerve can regenerate after lesion, we have used this animal model (1) to study if the phosphorylated form of MAP1B can be found in the CNS of the fish, (2) to study the expres- Neuroscience Letters 245 (1998) 93–96 0304-3940/98/$19.00  1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00188-8 * Corresponding author. Tel.: +34 4 4647700 ext. 3082; fax: +34 4 4648966; e-mail: gcpvecoe@lg.ehu.es