An explanation of unexpected Hoxd expressions in mutant mice

The Hox gene collinearity enigma has often been approached using models based on biomolecular mechanisms. The 'biophysical model', is an alternative approach, speculating that collinearity is caused by physical forces pulling the Hox clusters from a territory where they are inactive to a distinct spatial domain where they are activated in a step by step manner. Hox gene translocations have recently been observed in support of the biophysical model. Furthermore, genetic engineering experiments, performed in embryonic mice, gave rise to some unexpected mutant expressions that biomolecular models could not predict. In several cases when anterior Hoxd genes are deleted, the expression of the genes whose expression is probed in the mutants are 'impossible to anticipate'. On the contrary, the biophysical model offers convincing explanation. All these experimental results support the idea of physical forces being responsible for Hox gene collinearity. In order to test the validity of the various models further, certain experiment involving gene deletions are proposed. The biophysical and biomolecular models predict different results for these experiments, hence the expected outcome will confirm or question the validity of these models.