FRAP ANALYSIS OF THE STABILITY OF THE MICROTUBULE POPULATION ALONG THE NEURITES OF CHICK SENSORY NEURONS

In order to study microtubule turnover in elongating neurites, chick e mbryo sensory neurons were microinjected with x-rhodamine tubulin, and after 6-12 hours, short segments along chosen neurites were photoblea ched at multiple sites. Previous studies [Lim et al., 1989; 1990] indi cated that recovery of fluorescence (FRAP) in neurites occurs by the d ynamic turnover of stationary microtubules. In all cases, distal bleac hed zones recovered fluorescence faster than bleached zones more proxi mally located along the same neurites. Bleached zones at growth cones completely recovered in 30-40 minutes, while bleached zones located mo re proximally usually recovered in 50-120 minutes. In the most proxima l regions of long neurites, recovery of fluorescence was often incompl ete, indicating that a significant fraction of the microtubules in the se regions were very stable. These studies indicate that there are dif ferences in microtubule stability along the length of growing neurites . These differences may arise from the combined effects of 1) modifica tions that stabilize and lengthen microtubules in maturing neurites an d 2) the dynamic instability of the distally oriented microtubule plus ends.