Developmental Pathways

Developmental and Signaling Pathways: Hox cluster organization in Drosophila and mouse

Mallo, M. and Alonso, C. R. (2013). The regulation of Hox gene expression during animal development. Development 140: 3951-3963. PubMed ID: 24046316

Legend: Organisation of Hox clusters in Drosophila and mouse The Drosophila Hox genes (top) are grouped into two genomic clusters: the Antennapedia (ANT-C) and Bithorax clusters (BX-C). Expression domains of the individual Hox genes within the ANT-C and BX-C along the anteroposterior (AP) axis of the fruitfly embryo match the array of the genes along the chromosome, displaying a property termed collinearity. Experiments in the late 1980s revealed that mice also possess a set of Hox genes (bottom) similar to those found in Drosophila and that their organisation along the chromosome as well as their order of expression along the AP axis also displayed collinearity. An important difference between these two systems is that the mouse has four clusters (Hoxa, Hoxb, Hoxc and Hoxd) instead of one, as a result of two rounds of gene duplication. The Hox complement of the mouse also reveals that some individual Hox genes have been duplicated whereas others have been lost in each cluster. Based on sequence and genomic comparisons across a wide range of phyla, the structure of the cluster ancestral to insects and mammals can be inferred (middle). Several microRNAs (miRNAs) are also encoded within the Drosophila and mouse Hox clusters, and many of these miRNAs have been shown to target Hox genes. Furthermore, the relative position of many of these miRNA genes in reference to nearby Hox genes appears to be invariant despite substantial periods of evolution, suggesting that the position of miRNA genes might be functionally constrained. In the mouse, paralogue groups (PGs) 1-13 are indicated (Mallo, 2013). Adapted from Carroll, 1995..

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