MicroRNAs in the Hox network: an apparent link to posterior prevalence

Homeobox (Hox) transcription factors confer anterior - posterior (AP) axial coordinates to vertebrate embryos. Hox genes are found in clusters that also contain genes for microRNAs (miRNAs). Our analysis of predicted miRNA targets indicates that Hox cluster- embedded miRNAs preferentially target Hox mRNAs. Moreover, the presumed Hox target genes are predominantly situated on the 3' side of each Hox miRNA locus. These results suggest that Hox miRNAs help repress more anterior programmes, thereby reinforcing posterior prevalence, which is the hierarchical dominance of posterior over anterior Hox gene function that is observed in bilaterians. In this way, miRNA- mediated regulation seems to recapitulate interactions at other levels of gene expression, some more ancestral, within a network under stabilizing selection.