4 REPEAT HIGH-MOL-WT MAP2 FORMS IN RAT DORSAL-ROOT GANGLIA

The high-mel-wt forms of brain microtubule-associated protein 2 (MAP2a /b) segregate within the dendrites during neuronal differentiation, wh ereas a low-mel-wt variant, MAP2c, is distributed within all the neuro nal domains. Both MAP2b and MAP2c contain three tubulin binding repeat s, whereas another low-mel-wt form, MAP2d, contains four repeats. Sinc e high-mol-wt MAP2 species with four repeats have been cloned so far o nly from the sensory ND cell line, we have studied in this work the hi gh-mel-wt forms expressed by dorsal root ganglia (DRG). Different clon es obtained from PCR amplification products of portions of the C-termi nal and of the 3' end of the middle MAP2b domains contained either thr ee or four tubulin binding repeats at adult stages and only three post natally. In adulthood, two exons located at the 3' end of the MAP2b mi ddle domain Mi ere missing in several clones: exon 10 within clones wi th three or four repeats, exon 11 only within those containing four re peats. Several other clones obtained from PCR amplification products o f portions of the N-terminal and of the 5' end of the middle MAP2b dom ains revealed exons 7A and 8. In contrast, Northern analysis revealed exon 8 but not exon 7A, which is probably expressed in trace amounts i n the DRG. In this article, we have identified for the first time high -mel-wt MAP2 transcripts containing four tubulin binding repeats that seem to be expressed only by the DRG and also differing from brain MAP 2b by a number of other exons.