How transcription factors achieve their in vivo specificities is a fundamental question in biology. For the Homeotic Complex (HOM/Hox) family of homeoproteins, specificity in vivo is likely to be in part determined by subtle differences in the DNA binding properties inherent in these proteins. Some of these differences in DNA binding are due to sequence differences in the N‐terminal arms of HOM/Hox homeodomains. Evidence also exists to suggest that cofactors can modify HOM/Hox function by cooperative DNA binding interactions. The Drosophila (...) homeoprotein extradenticle (exd) is likely to be one such cofactor. In HOM/Hox proteins, both the conserved ‘YPWM’ peptide motif and the homeodomain are important for interacting with exd. Although exd provides part of the answer as to how specificity is achieved, there may be additional cofactors and mechanisms that have yet to be identified. (shrink)

How size is controlled during animal development remains a fascinating problem despite decades of research. Here we review key concepts in size biology and develop our thesis that much can be learned by studying how different organ sizes are differentially scaled by homeotic selector genes. A common theme from initial studies using this approach is that morphogen pathways are modified in numerous ways by selector genes to effect size control. We integrate these results with other pathways known to regulate organ (...) size in developing a comprehensive model for organ size control. ©2007 Wiley Periodicals, Inc BioEssays 30:843–853, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

The evolutionarily conserved genomic organization of the Hox genes has been a puzzle ever since it was discovered that their order along the chromosome is similar to the order of their functional domains along the antero‐posterior axis. Why has this colinearity been maintained throughout evolution? A close look at regulatory sequences from the mouse Hox clusters(1,2) suggests that enhancer sharing between adjacent Hox genes may be one reason. Moreover, characterizing the activity of one of these mouse enhancers in Drosophila(2) illustrates (...) that despite many similarities, not all Hox clusters are built in the same way. (shrink)