PROTEIN UBIQUITINATION AND NEURONAL DIFFERENTIATION IN CHICK-EMBRYOS

Ubiquitin is a small highly conserved intracellular protein which is i nvolved in a number of cellular functions including targeting proteins for degradation. We have studied the distribution of ubiquitin-protei n conjugates and two enzymes involved in protein ubiquitination in chi ck embryos. Using immunocytochemical techniques, we have observed that chick neural crest cells and dorsal root ganglia acquire immunoreacti vity in their nuclei and cytoplasm as they mature, both in vivo and in vitro, though they are not immunoreactive at early stages of developm ent. Immunoreactivity for the ubiquitin activating enzyme (E1) and a c arboxyl terminal hydrolase for ubiquitin (PGP 9.5) also appears in the nuclei of differentiating neurons at the same time as ubiquitin-prote in conjugates. Our results provide evidence that the nuclear accumulat ion of ubiquitin-protein conjugates is closely associated with maturat ion of neurons towards a differentiated phenotype.