DEVELOPMENTAL EXPRESSION OF THE MOUSE EVX-2 GENE - RELATIONSHIP WITH THE EVOLUTION OF THE HOM HOX COMPLEX/

The mouse Evx-2 gene is located in the immediate vicinity of the Hoxd- 13 gene, the most posteriorly expressed gene of the HOXD complex. Whil e the Evx-1 gene is also physically linked to the HOXA complex, it is more distantly located from the corresponding Hoxa-13 gene. We have an alysed the expression of Evx-2 during development and compared it to t hat of Evx-1 and Hoxd-13. We show that, even though Evx-2 is expressed in the developing CNS in a pattern resembling that of other Evx-relat ed genes, the overall expression profile is similar to that of the nei ghbouring Herd genes, in particular with respect to the developing lim bs and genitalia. We propose that the acquisition of expression featur es typical of Hox genes, together with the disappearance of some expre ssion traits common to Evx genes, is due to the close physical linkage of Evx-2 to the HOXD complex, which results in Evx-2 expression being partly controlled by mechanisms acting in the HOX complex. This trans position of the Evx-2 gene next to the Hoxd-13 gene may have occurred soon after the large scale duplications of the HOX complexes. A scheme is proposed to account for the functional evolution of eve-related ge nes in the context of their linkage to the HOM/Hox complexes.