Homeotic genes are aligned on the chromosome in the order of the segments that they specify along the antero-posterior axis of the @entity238 . In general the genes affecting the more posterior segments repress the more anterior genes, a phenomenon known as "posterior dominance". There is however a noticeable exception to this rule in the central nervous system of @entity238 where the posterior @entity4533 gene does not repress the immediately more anterior @entity4534 gene. Instead, @entity4534 repression is accomplished by a 92 kb-long ncRNA (the @entity68157 ) that is transcribed from the large inter-genic region between @entity4534 and @entity4533 . This @entity68157 encodes a microRNA to repress @entity4534 and also a second redundant repression mechanism acting in cis and thought to be transcriptional interference with the @entity4534 promoter. Using in situ hybridization, a previous work suggested that the @entity68157 transcript forms discrete foci restricted to the nuclear periphery and that this localization may be important for its function. In order to better characterize the intra-cellular localization of the @entity68157 we used the MS2-MCP system, which allows fluorescent labeling of RNA in cells and relies on the interaction between GFP-tagged MS2 coat protein (MCP-GFP) and MS2 RNA stem loops. Our results indicate that the large foci seen in previous studies correspond to the site of @entity68157 transcription and that the foci seen may simply be an indication of the level of transcription at the locus. We find no evidence to suggest that this localization is important for its function on @entity4534 repression. We discuss the idea that the @entity68157 may be a relic of a more general ancient mechanism of posterior dominance during the emergence of the hox clusters that was mediated by transcriptional interference.

Following the intracellular localization of the XXXX of the bithorax complex using the MS2-MCP-GFP system.

@entity4534 :: ('42037(Tax:7227)', 'Gene') :: ['abd-A'] @entity4533 :: ('47763(Tax:7227)', 'Gene') :: ['Abd-B'] @entity68157 :: ('12798430', 'Gene') :: ['iab-8ncRNA', 'iab8ncRNA'] @entity238 :: ('7227', 'Species') :: ['Drosophila melanogaster', 'fly']
@entity68157 :: (12798430,Gene) :: ['iab-8ncRNA']
