NUCLEAR-PORE COMPLEX STRUCTURE IN BIRDS

The nuclear envelope consists of two parallel membranes enclosing an a queous lumen. In places there are pores in both membranes at which the two membranes are joined. Within these pores reside the nuclear pore complexes. The current structural models of the nuclear pore complex h ave been derived from a number of studies using different electron mic roscopical techniques. Recently, using surface imaging techniques such as held emission in-lens scanning electron microscopy, novel structur es have been identified, particularly at the periphery of the structur e, most notably the nucleoplasmic basket. One limitation of the curren t models is that they are based almost entirely on nuclear envelopes i solated from amphibian oocytes and a pressing question is whether this structure is the same in other organisms and tissues. Here we have st udied the structure of nuclear envelopes isolated from bird oocytes. W e show that the overall structure is remarkably conserved. In particul ar, recently discovered peripheral structures appear very similar. We see variations in basket conformation but believe that this is related to the functional states of individual pore complexes. (C) 1997 Acade mic Press.