Expression of microtubule-associated protein-2a and other novel microtubule-associated protein-2 transcripts in human fetal spinal cord

In human fetal spinal cord (HFSC), six additional microtubule- associated protein-2 (MAP-2) transcripts are generated by alternative splicing of two recently described exons, exon 8 and exon 13. The following three translated proteins are detected by western blot analysis: MAP-2b expressing exon 8 (MAP-2b+8; MAP-2a), MAP-2b expressing exon 13 (MAP-2b+13), and MAP-2c expressing exon 8 and exon 13 (MAP-2c+8+13). The finding that MAP- 2b+8 is expressed in HFSC demonstrates for the first time the presence of MAP-2a in human fetal CNS. Immunocytochemical studies show that exon 8- specific antibody and exon 13-specific antibody stain independent and overlapping populations of neurons in the lumbar region of the HFSC. Antibody 13-immunopositive neurons have predominantly cytosolic staining, whereas in the antibody 8-immunoreactive neurons staining was observed in the cytosol, dendrites, and some synapses. The prenatal expression of MAP-2a, which has been used as a marker of synaptogenesis, not only demonstrates the presence of a mature MAP-2 isoform in HFSC, but suggests that MAP-2a is important during human fetal as well as post-natal synaptogenesis.