Nuclear compartmentalization is believed to be essential for many processes. Splicing factors, for example, reside in discrete compartments (SFCs) with which active genes associate, and localization of genes to particular nuclear regions could constitute an important regulatory mechanism. But to what extent are changes in nuclear organization associated with tissue-specific gene expression in vivo rather than simply characteristic of transformed cell lines? Regina Armstrong and co-workers have examined nuclear organization during differentiation of primary oligodendrocyte cultures, which closely mimics in vivo oligodendrocyte differentiation (see p. 4071). Using genomic in situ hybridization, they show that PLP, a gene upregulated during oligodendrocyte differentiation, is associated with the nuclear periphery in both progenitor cells and differentiated oligodendrocytes and remains spatially separated from a coordinately regulated gene, MBP. The authors do, however, find that PLP transcription in differentiated cells induces local formation of SFCs and demonstrate that these are not associated with inactive genes. They therefore conclude that nuclear reorganization does occur during differentiation but is characterized by changes in the distribution of proteins such as splicing factors rather than gene localization/clustering.
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