Nucleolar substructures of rabbit cleaving embryos: an immunocytochemical study

Area of Science:

• Developmental Biology
• Cell Biology
• Molecular Biology

Background:

• Nucleologenesis, the formation of nucleoli, is a complex process crucial for cell function.
• In preimplantation rabbit embryos, nucleologenesis is asynchronous and spans multiple cell cycles.
• Understanding the dynamic changes in nucleolar substructures is key to comprehending early embryonic development.

Purpose of the Study:

• To investigate the structure-function relationships of nucleolar substructures during rabbit preimplantation development.
• To determine the temporal and spatial localization of DNA, RNA, and key nucleolar proteins during nucleologenesis.
• To correlate the morphological changes of nucleoli with the onset of their function, particularly rDNA transcription.

Main Methods:

• Immunocytochemistry with light and electron microscopy for protein and RNA localization.
• Nick translation and terminal deoxynucleotidyl transferase assays for DNA detection.
• Analysis of nucleolar protein distribution (fibrillarin, nucleolin, protein B23) during different embryonic stages.

Main Results:

• DNA initially localized to the periphery of nucleolar precursor bodies (NPBs) and later associated with the dense fibrillar component (DFC) in reticulated nucleoli.
• RNA was first detected at the 16-cell stage, associated with the DFC and within the residual body.
• Key nucleolar proteins showed dynamic redistribution, accumulating around NPBs during activation and forming distinct patterns in mature nucleoli.

Conclusions:

• Nucleologenesis is completed by the fourth cell cycle in cleaving rabbit embryos.
• The establishment of nucleolar structure is closely correlated with the onset of nucleolar function, marked by detectable RNA.
• The observed reorganization of nucleolar components is linked to the activation of rDNA transcription.