Evx2-Hoxd13 intergenic region restricts enhancer association to Hoxd13 promoter.

Expression of Hox genes is tightly regulated in spatial and temporal domains. Evx2 is located next to Hoxd13 within 8 kb on the opposite DNA strand. Early in development, the pattern of Hoxd13 expression resembles that of Evx2 in limb and genital buds. After 10 dpc, however, Evx2 begins to be expressed in CNS as well. We analyzed the region responsible for these differences using ES cell techniques, and found that the intergenic region between Evx2 and Hoxd13 behaves as a boundary element that functions differentially in space and time, specifically in the development of limbs, genital bud, and brain. This boundary element comprises a large sequence spanning several kilobases that can be divided into at least two units: a constitutive boundary element, which blocks transcription regulatory influences from the chromosomal environment, and a regulatory element, which controls the function of the constitutive boundary element in time and space.