The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation: II. The immature oocyte and dynamic aspects

Abstract

Different stages of oogenesis of the Alpine newt were compared with respect to the nuclear envelope structure, employing negative staining and sectional work: larval eggs, early and later lampbrush stages, and mature eggs. While in all the stages the general components of the nuclear pore complexes could be observed, differences were found concerning quantitative structural data. In particular the frequency of pores containing a central granule decreased from 61 % in the larval to 36 % in the mature egg. Some new information on the mode of nucleocytoplasmic transit of nucleolus-derived material could be obtained from the lampbrush stage eggs. In this stage, fibrillar strands spinning out from the nucleolar periphery can be seen in contact with the nuclear pore complex, expecially with the inner annular granules. Furthermore, dense spheres of nucleolar material migrate through the central channel of the pore in a rodlike configuration in the very same mode that has been described for salivary glands of Chironomus thummi (69). Alternative relationships of nucleocytoplasmic RNP transport to the constituents of the nuclear pore complex are discussed.