This study employed porcine oocyte developmental biology as translational model investigating epigenetics in oocyte maturation. Previously, studies in various species confirmed that the chromatin of oocytes is subjected to large-scale modifications correlated to transcriptional silencing during final maturation. These modifications seem essential both for completion of the oocyte’s meiosis and subsequent embryonic developmental success. In the present study, we focused on a putative interconnection between nucleolar transcriptional activity and spatial chromatin organization towards completion of oocyte growth. Porcine cumulus-oocyte-complexes (COCs) were aspirated from >3mm follicles of abattoir material. 300 COCs were then divided into 2 groups, pre-categorized by supravital brilliant-cresyl-blue (BCB) staining into fully mature (BCB+) and still maturating (BCB-). Following denuding and fixation, oocytes, with the same proportion of BCB- and BCB+ groups, were processed for 3D-immunofluorescence (n=140) using antibodies against upstream binding factor (UBF; nucleolar activity), H3K9me3 and centromeric protein A and B (CENP) as epigenetic heterochromatin markers, as well as for 3D-DNA-FISH (n=140) with fluorescent oligonucleotides specific for porcine meta- and acrocentric heterochromatin sequences. Finally, oocytes (n=20) were prepared for TEM according to standard protocol. Analysis by high-resolution microscopy included confocal and TEM. Qualitative assessment of cellular ultrastructure by TEM revealed distinct differences between BCB+ and BCB- oocytes and supported BCB-staining as viable method for rough categorization regarding maturation status. Immunostaining and labeling of chromatin allowed to detect all chromatin conformations (as previously described), from non-surrounded nucleolus (NSN) to surrounded nucleolus (SN) and their intermediate conformations (pNSN, pSN) in both BCB groups. However, the BCB+ group contained a higher percentage of oocytes expressing chromatin conformations categorized as mature, whereas the opposite was true for the BCB- group. UBF-activity was only present in NSN and pNSN categorized oocytes and detected significantly more often in the BCB- group. The distribution of centromeric (CENP) and pericentromeric chromatin (H3K9me3) as well as repeated sequences DNA-FISH signal displayed distinct changes in their 3D-organization between NSN an SN conformation, characterized by significant signal-condensation around the nucleolus towards final maturation. Altogether these results demonstrated that oocytes from the BCB+ group, which correspond to mature oocytes with higher competency for embryonic development, display specific spatial 3D-chromatin organization patterns of both oligonucleotide sequences and epigenetic marks for constitutive heterochromatin related to final oocyte maturation.