Nuclear envelope disease and chromatin organization

Nucleosome functions in spindle assembly and nuclear envelope formation

Chromosomes are not only carriers of the genetic material, but also actively regulate the assembly of complex intracellular architectures. During mitosis, chromosome-induced microtubule polymerisation ensures spindle assembly in cells without centrosomes and plays a supportive role in centrosome-containing cells. Chromosomal signals also mediate post-mitotic nuclear envelope (NE) re-formation. Recent studies using novel approaches to manipulate histones in oocytes, where functions can be analysed in the absence of transcription, have established that nucleosomes, but not DNA alone, mediate the chromosomal regulation of spindle assembly and NE formation. Both processes require the generation of RanGTP by RCC1 recruited to nucleosomes but nucleosomes also acquire cell cycle stage specific regulators, Aurora B in mitosis and ELYS, the initiator of nuclear pore complex assembly, at mitotic exit. Here, we review the mechanisms by which nucleosomes control assembly and functions of the spindle and the NE, and discuss their implications for genome maintenance.

AAGAG repeat RNA is an essential component of nuclear matrix in Drosophila

Eukaryotic nucleus is functionally as well as spatially compartmentalized and maintains dynamic organization of sub-nuclear bodies. This organization is supported by a non-chromatin nuclear structure called the nuclear matrix. Although the precise molecular composition and ultra-structure of the nuclear matrix is not known, proteins and RNA molecules are its major components and several nuclear matrix proteins have been identified. However, the nature of its RNA component is unknown. Here we show that in Drosophila melanogaster, transcripts from AAGAG repeats of several hundred nucleotide in length are critical constituents of the nuclear matrix. While both the strands of this repeat are transcribed and are nuclear matrix associated, the polypurine strand is predominantly detected in situ. We also show that AAGAG RNA is essential for viability. Our results reveal the molecular identity of a critical RNA component of the nuclear architecture and point to one of the utilities of the repetitive part of the genome that has accumulated in higher eukaryotes.