Peculiarities of the molecular composition of heterochromatin associated with pronucleoli in mouse embryos

The nucleus of pre-implantation mammalian embryos is characterized by peculiar structural organization. At the initial stages of cleavage, the nucleus of the embryo contains the so-called nucleolus precursor bodies (NPBs) or pronucleoli rather than functionally active nucleoli. The NPBs are fibrillar electron-dense structures inactive in RNA synthesis. The vast majority of NPBs are surrounded by a ring-shaped zone of transcriptionally inactive heterochromatin. Intriguingly, these zones contain not only tri-methylated histone Н3K9me3 as an epigenetic mark of repressed chromatin but also acetylated histone H4K5ac, a well-known marker of active chromatin. Immunocytochemical data suggest that the molecular composition of this ‘ring heterochromatin’ in mouse embryos changes during the realization of embryonic genome activation events, as well as during artificial suppression of transcription. In zygotes, some factors of mRNA biogenesis including splicing factor SC35 (SRSF2) and basal transcription factor TFIID are detectable in the ring chromatin. At later stages of development, other nuclear proteins such as Y14, a core component of the exon-exon junction complex (EJC), as well as the proteins involved in chromatin remodeling (ATRX, Daxx) are also detectable in this area. A typical component of the ‘ring heterochromatin’ is actin. Anti-actin immunocytochemical labeling is most expressed at the two-cell cleavage stage after activation of the embryonic genome. Indicatively, the molecular composition of the ‘ring heterochromatin’ associated with different NPBs may differ significantly even in the same nucleus. This seems to reflect the functional heterogeneity of morphologically similar NPBs according to their competence to the process of nucleologenesis. Here, we discuss briefly some peculiarities of the molecular composition and possible functions of the NPB-associated heterochromatin in mouse early embryos

mRNA accumulation in the Cajal bodies of the diplotene larch microsporocyte

In microsporocytes of the European larch, we demonstrated the presence of several mRNAs in spherical nuclear bodies. In the nuclei of microsporocytes, we observed up to 12 bodies, ranging from 0.5 to 6 μm in diameter, during the prophase of the first meiotic division. Our previous studies revealed the presence of polyadenylated RNA (poly(A) RNA) in these bodies, but did not confirm the presence of nascent transcripts or splicing factors of the SR family. The lack of these molecules precludes the bodies from being the sites of synthesis and early maturation of primary transcripts (Kołowerzo et al., Protoplasma 236:13–19, 2009). However, the bodies serve as sites for the accumulation of splicing machinery, including the Sm proteins and small nuclear RNAs. Characteristic ultrastructures and the molecular composition of the nuclear bodies, which contain poly(A) RNA, are indicative of Cajal bodies (CBs). Here, we demonstrated the presence of several housekeeping gene transcripts—α-tubulin, pectin methylesterase, peroxidase and catalase, ATPase, and inositol-3-phosphate synthase—in CBs. Additionally, we observed transcripts of the RNA polymerase II subunits RPB2 and RPB10 RNA pol II and the core spliceosome proteins mRNA SmD1, SmD2, and SmE. The co-localization of nascent transcripts and mRNAs indicates that mRNA accumulation/storage, particularly in CBs, occurs in the nucleus of microsporocytes

Composition of organic matter from black shales drilled in the Cape Verde Basin in DSDP Hole 41-367

Results of geochemical studies of organic matter in black shales from the Cape Verde Basin are reported. Based on these results, in combination with data of petrographic analysis, conclusions are made about sapropelic nature of their organic matter and low degree of its coalification. It corresponds to the proto-catagenetic substage of sedimentary rocks. Black shales of the Cape Verde Basin are classified as potential oil source strata