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GONZALO GIMÉNEZ MARTÍN ANAL. REAL ACAD. FARM.

La existencia del NOR no siempre asegura la reorganización de un nucleolo.
Puede existir dominancia de unos NORs sobre otros, tanto inter- como intra-específicos,
formándose un número de nucleolos inferior al número de NORs, debiéndose a proteínas
de unión al DNA condicionadas por el nivel de metilación de sus citosinas. Esta
dominancia en la nucleologénesis es detallada en sus diferentes fases.
Palabras clave: Transcripción celular.- Nucleologénesis

SUMMARY

Reinitiation of the Transcription in the celular cycle. Nucleologenesis

The transition from a telophase to the G1 of a new cell cycle includes the
nucleologenesis process o nucleolar reorganization. In it, specific chromosomal regions
of the karyitype, the nucleolar organizer regions (NORs) are involved in the
development of the new nucleoli responsible for the synthesis of ribosomal RNAs in the
cell.

Synthesis of both RNA and proteins are cancelled or very low in the central
stages of mitosis. They re-start or increase again by telophase completion, when many
small prenucleolar bodies appear on the surface of chromosomes.

To assess how the reinitiation of RNA and protein synthesis at the beginning of
the new cycle affect the nucleologenesis process, three premises were used: a)
synchronous telophases become binucleate cells in eartly G1 if blocking their
cytokinesis by caffeine; b) the whole nucleologenesis takes place in a time window that
represent only 7.4% of the whole cell cycle duration, RNA or protein synthesis at
different times of the nucleologenesis process. They were used for the kinematic study of
the process.

It was shown, for the first time, that the prenucleolar bodies were not product of
nay concurrent RNA synthesis taking place after metaphase. Moreover, their appearance
was also independent from the reinitiation of the mature nucleoli were growing, the
advancement in the completion of the nucleologenesis when the simultaneous protein
synthesis was prevented, and their inhibition when the re-start of rDNA synthesis was
prevented, allowed to design a model integrating the different factors involved in
nucleolar formation.

Lastly, it is a long standing fact that the presence of a NOR does not always
ensure the development of a nucleolus on it. Thus, a NOR could result active (dominant)
in developing a nucleolus versus okther interspecific, independent from the normal
fusion of nucleoli formed in different NORs. Nucleolar dominance or amphiplastia can
be achieved by selective hypomethylation of cytosines in certain NORs. The factors
involved in such process has been determined.
Key words: Celular transcription.- Nucleologenesis.

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