STRUCTURAL AND FUNCTIONAL MODIFICATIONS OF THE NUCLEOLUS DURING PREVITELLOGENIC OOCYTE GROWTH IN THE LIZARD PODARCIS-SICULA

In the present study we analyse the nature and the functional signific ance of the spherical and fibrillo-granular structures appearing in th e oocyte nucleus of the lizard Podarcis sicula, following the disappea rance of the typical nucleolus. By LM and TEM approaches, we demonstra te that the fibrillogranuli, containing DNA, RNA and nucleolar protein s, are micronucleoli transcriptionally active and that their DNA is pr obably derived from nucleolar fragmentation. By contrast, we could not explain the origin and role of the so-called spherical bodies, appear ing earlier in oocyte growth; these, in fact, do not contain nucleic a cids or nucleolar proteins and do not incorporate uridine. Different p ossible explanations of their significance ave discussed. Mol. Reprod. Dev. 51:413-420, 1998. (C) 1998 Wiley-Liss, Inc.