Localization of satellite DNA and associated proteins in respect to nucleolar precursor bodies in one- and two-cell mouse embryos

Abstract

Nucleolar precursor bodies (NPB) are characteristic structures in the nuclei of one- and two cell mouse embryos. The alignment of centromeric (CEN) and pericentromeric (periCEN) chromosome regions to the chromatin layer surrounding NPB is known. Mus musculus 4 satellite DNA (satDNA) types are known to be located in CEN region--mouse minor satellite (MiSat) and mouse satellite 3 (MS3); and periCEN region--mouse major satellite (MaSat) and mouse satellite (MS4). We determined the localization of 4 types of mouse satDNA CEN and periCEN regions and associated proteins: RNA-helicase p68, SMC3, Rad21 subunits of the cohesin complex and SYCP3 subunit of the synaptonemal complex (SC). Partially flattened nuclei of the one- and two-cell embryos and embryos treated with ocadaic acids (OA) were used. Different satDNA fragments revealed distinct domains at the surface of NPB: periCEN MaSat was always localized in NPB more internally covering almost entire surface of NPB while CEN MiSat, MS3 and periCEN MS4 showed more peripheral localization. All 4 satDNA did not cover the entire areas of the NPB, indicating the presence of other DNA sequence involved in its formation. RNA-helicase p68 and components of multiprotein cohesin and synaptonemal complexes are the necessary components of NPB. Our results support the opinion that NPB serve as a precursor of chromocenters.