Antisense MAP-2 oligonucleotides induce changes in microtubule assembly and neuritic elongation in pre-existing neurites of rat cortical neurons

Microtubule-associated protein 2 (MAP-2) is an abundant component of the cytoskeleton present in dendrites and cell bodies of neurons of the CNS. To examine the biological function of MAP-2, two MAP-2 antisense (AS) oligonucleotides complementary to the 5' region of the rat MAP-2 cDNA were added to rat primary embryonic day 17-18 (E17-18) cultured cortical neurons 24 h after plating and neurite outgrowth and morphology studied. The treatment of primary cortical cultures with either of the two MAP-2 AS oligonucleotides resulted in decreased MAP-2 and reduction in the number of neuritic processes relative to the control or MAP-2 sense-treated cultures. By immunostaining and light microscopy the AS-treated neurons appeared smaller, more rounded, and less intensely stained for MAP-2 than the untreated or the MAP-2 sense-treated cultures. By electron microscopy disorganized microtubules and a reduction in the number of microtubules within neurites of the AS-treated cultures were observed. We conclude that MAP-2 continues to be required for microtubule spacing and stability within neurites once they have formed.