Fig. (2). Mechanical analogue of Hox cluster decodensation and extrusion.

a) Before activation the Hox cluster is condensed inside the chromatin territory (CT)-(left). Mechanical analogue: an uncharged elastic spring fixed at its left end (right).

b) The cluster is slightly decondenced and Hox1 is extruded in the interchromosome domain (ICD) in the area of the transcription factory (TF -red disc) (left). A small force F1 is applied at the loose end and expands slightly the spring (right).

c) The cluster is further decondenced and the extruded Hox2 is located in the transcription factory area while Hox1 moves away from TF (left). A bigger force F2 > F1 expands further the spring (right).

d) The posterior fixed end of the spring is cut off. A small force F1 expands and shifts the spring as in c).