Fig. 8. Overexpression of Cdk5-p35 increases NF bundling in perikarya. DRG neurons before (–) and 24 hours after (+) transfection with constructs expressing Cdk5 and p35 are shown in all panels (first two panels have no +/– label). Neurons in panels `NF-H' and `NF-L' were immunostained with antibodies directed against these subunits to reveal the distribution of endogenous NFs with (right) and without (left) overexpressing Cdk5-p35. Panels labeled `Biotin-L' and `GFP-M' show representative perikarya of neurons 2 hours after microinjection of biotin-L with (+) or without (–) Cdk5-p35 (followed by immunostaining with anti-biotin) or 24 hours following transfection with a construct expressing GFP-M with (+) or without (–) Cdk5-p35. Notice that perikarya of neurons overexpressing Cdk5-p35 displayed thick filamentous profiles containing endogenous subunits, microinjected subunits and subunits expressed following transfection. By contrast, endogenous and exogenous subunits in perikarya of neurons not overexpressing Cdk5-p35 were diffuse, punctate or present as relatively fine filaments that exhibited a much smaller caliber than those of cells overexpressing Cdk5-p35. Panels labeled `RT97' show representative neurons transfected with GFP-M with (+) or without (–) Cdk5-p35 then immunostained with RT97 to reveal the distribution of NF phospho-epitopes in perikarya. Notice the increase in perikaryal RT97 immunoreactivity in perikarya of neurons transfected with Cdk5-p35 and the association of RT97 with the resultant thick filamentous profiles, indicating that perikaryal NF bundles contain phospho-NFs.