(A) Partitioned neuron cultures, which isolate cell bodies (CB) from distal axons (DA), were used to assess retrograde neuron survival when NGF was applied to the microfluidically isolated DA compartment using Bisbenzimide (Bis) to label nuclear DNA (green) and fluorescent microspheres (FS) to identify neurons that extended axons into the DA compartment and retrogradely transported them (red). Apoptotic neurons were identified by condensed, fragmented or absent nuclear DNA. Apoptotic cells not containing retrogradely transported FS (^†) were not scored, but apoptotic FS-containing neurons (FS⁺, arrowhead) and healthy FS⁺ neurons with open chromatin and punctate nucleoli (arrow) were scored. Scale bar: 20 μM. (B) Whereas most neurons survived when 10 ng/mL NGF was present in the DA compartment in TCtl neurons, there is significantly less survival of TcKO neurons even when NGF was escalated 50-fold in the DA compartment (Student’s t test; *P = 0.007, n = 3–6; **P = 0.004, n = 4; ***P = 0.04, n = 3). (C) TcKO neurons differentiated in partitioned cultures and infected with doxycycline-inducible adenoviruses showed highly significant NGF-dependent survival abnormalities when only GFP was expressed in them (Student’s t test; *P < 0.0001, n = 7), and their retrograde survival was completely rescued when Elp1 expression was restored (n = 3). Expression of nuclear localized Elp1 (Elp1-nuc) showed highly significant retrograde survival abnormalities (Student’s t test; **P < 0.001, n = 7) and no significant rescue of retrograde survival relative to GFP⁺/FS⁺ infected TcKO neurons (Student’s t test; NS, P = 0.12). Expression of cytoplasm localized Elp1 (Elp1-cyto) completely rescued retrograde neuron survival (n = 4). For C, results were considered significant if the Bonferroni’s corrected P value was less than 0.013.