IMMUNOCYTOCHEMICAL LOCALIZATION OF MICROTUBULE-ASSOCIATED PROTEIN-1B AND PROTEIN-2 IN THE DEVELOPING RAT SPINAL-CORD

The straightforward anatomical organisation of the developing and matu re rat spinal cord was used to determine and interpret the time of app earance and expression patterns of microtubule-associated proteins (MA P) 1b and 2. Immunoblots revealed the presence of MAP1b and 2 in the e arly embryonic rat spinal cord and confirmed the specificity of the us ed anti-MAP mouse monoclonal antibodies. The immunocytochemical data d emonstrated a rostral-to-caudal and ventral-to-dorsal gradient in the expression of MAP1b/2 within the developing spinal cord. In the matrix layer, MAP1b was found in a distinct radial pattern distributed betwe en the membrana limitans interna and externa between embryonal day (E) 12 and E15. Immunostaining for vimentin revealed that this MAP1b patte rn was morphologically and topographically different from the radial g lial pattern which was present in the matrix layer between E13 and E19 . The ventral-to-dorsal developmental gradient of the MAP1b staining i n the spinal cord matrix layer indicates a close involvement of MAP1b either in the organisation of the microtubules in the cytoplasmatic ex tensions of the proliferating neuroblasts or neuroblast mitosis. MAP2 could not be detected in the developing matrix layer. In the mantle an d marginal layer, MAP1b was abundantly present between E12 and postnat al day (P)0. After birth, the staining intensity for MAP1b gradually d ecreased in both layers towards a faint appearance at maturity. The di stribution patterns suggest an involvement of MAP1b in the maturation of the motor neurons, the contralaterally and ipsilaterally projecting axons and the ascending and descending long axons of the rat spinal c ord. MAP2 was present in the spinal cord grey matter between E12 and m aturity, which reflects a role for MAP2 in the development as well as in the maintenance of microtubules. The present description of the exp ression patterns of MAP1b and 2 in the developing spinal cord suggests important roles of the two proteins in various morphogenetic events. The findings may serve as the basis for future studies on the function of MAP1b and 2 in the development of the central nervous system.