Antony J. Durston*,1, Hans J. Jansen1, Paul In der Rieden2 and Michiel H.W. Hooiveld3
1Institute of Biology, University of Leiden, Sylvius Laboratory, Wassenaarseweg, Leiden, 2Studiekring, Utrecht, Mgr. van de Weteringstraat, Utrecht and 3Research Institute BCN-BRAIN, University Medical Center Groningen, University of Groningen, The Netherlands.
Hox collinearity is a spectacular phenomenon that has excited life scientists since its discovery in 1978. Two mechanisms have been proposed to explain the spatially sequential pattern of Hox gene expression in animal embryonic development: interactions among Hox genes, or the progressive opening of chromatin in the Hox clusters, from 3' to 5'. A review of the evidence across different species and developmental stages points to the universal involvement of trans-acting factors and cell-cell interactions. The evidence focuses attention on interactions between Hox genes and on the vertebrate somitogenesis clock. These novel conclusions open new perspectives for the field.