Hox genes are found in all metazoan phyla and are involved in specifying identity along the anterior‑posterior body axis. In arthropods, ten different classes of Hox genes can be distinguished, which are expressed in a typical staggered array along the anterior‑posterior axis of the embryo in...

There has been a great deal of interest in analysing the molecular evolution of the Hox cluster using both bioinformatic and experimental approaches. The posterior Hox genes have been of particular interest to both groups of biologists for a number of reasons: they appear to be associated with...

Once established, homeotic gene (Hox) expression is maintained in the original pattern by Polycomb‑group (PcG) and trithorax‑group (trxG) proteins therefore named maintenance proteins (MPs). PcG and trxG proteins maintain silencing and activation of Hox and many other genes, respectively. We...

Hox genes are prominently expressed in the developing brain and ventral ganglia of Drosophila. In the embryonic brain, the Hox genes labial and Deformed are essential for the establishment of regionalized neuronal identity; in their absence cells are generated in the brain but fail to acquire...

Despite apparently shared structural organisation and functional roles, vertebrate Hox genes are controlled by regulatory mechanisms rather distinct from those of the prototypic Drosophila Antennapedia (ANT‑C) and bithorax (BX‑C) complexes. If individual regulatory modules have been shown to...

Deciphering the molecular bases of animal body plan construction is a central question in developmental and evolutionary biology. Genome analyses of a number of metazoans indicate that widely conserved regulatory molecules underlie the amazing diversity of animal body plans, suggesting that these...

What is the function of the Hox genes? At first glance, it is a curious question. Indeed, the answer seems so obvious that several authors have spoken of ‘the Hox function’ about some of the Hox genes, namely Hox3/zen and Hox6/ftz that seem to have lost it during the evolution of Arthropods....

The loss in some taxa of conserved developmental control genes that are present in the vast majority of animal lineages is an understudied phenomenon. It is likely that in those lineages in which loss has occurred it may be a strong signal of the mode, tempo and direction of developmental...

Recent years have seen a plethora of ideas and hypotheses, and lots of debate, about the origin and evolution of the Hox gene cluster. Here I will attempt to summarize these hypotheses, identify their strengths and weaknesses and highlight the types of new data that may lead to further resolution...

For more than a century the origin of metazoan animals and for less than 3 years the early evolution of Hox genes has been debated. Both discussions are intrinsically tied together. New data from whole genome sequencing and recent progress in phylogeny of basal metazoans allow to provide an...

Insects have undergone dramatic evolutionary changes in extraembryonic development, which correlate with changes in the expression of the class‑3 Hox gene zen. Here, we review the evolution of this gene in insects and point out how changes in zen expression may have affected extraembryonic...

The discovery of the first homeotic mutation by Calvin Bridges in 19151 profoundly influenced the way we think about developmental processes. Although many mutations modify or deform morphological structures, homeotic mutations cause a spectacular phenotype in which a morphological structure...