Serial deletions and duplications suggest a mechanism for the collinearity of Hoxd genes in limbs

Abstract

Hox genes, located at one end of the HoxD cluster, are essential for the development of the extremities of our limbs; that is, the digits. This 'collinear' correspondence is accompanied by a gradual decrease in the transcriptional efficiency of the genes. To decipher the underlying regulatory mechanisms, and thus to understand better how digits develop, we engineered a series of deletions and duplications in vivo. We find that HoxD genes compete for a remote enhancer that recognizes the locus in a polar fashion, with a preference for the 5' extremity. Modifications in either the number or topography of Hoxd loci induced regulatory reallocations affecting both the number and morphology of digits. These results demonstrate why genes located at the extremity of the cluster are expressed at the distal end of the limbs, following a gradual reduction in transcriptional efficiency, and thus highlight the mechanistic nature of collinearity in limbs.

Anteroposterior patterning in the limb and digit specification: Contribution of mouse genetics

“…4) have further been recruited to pattern secondary axes such as the limb and the external genitalia. The involvement of the HoxD cluster in limb patterning is demonstrated by the effect of individual Hoxd mutations on digit shape, by the fact that Hoxa/Hoxd combined mutations affect specifically the formation of the different segments of the limb, and by the effect of specific manipulations in the HoxD cluster on the number and identity of digits (Capecchi, 1996;Favier and Dolle, 1997;Zakany and Duboule, 1999;Kmita et al, 2002). A role for Hoxd genes in localized activation of Shh has been unraveled more recently (Zakany et al, 2004).…”

“…Thanks to the work of the members of the Duboule laboratory, our understanding of the regulation of Hoxd gene expression in the limb has progressed remarkably over the past few years (Kmita et al, 2002;Spitz et al, 2003;Tarchini and Duboule, 2006). This advance is the result of a systematic application of the deletion/duplication strategy mentioned above (Herault et al, 1998).…”

“…It leads to expression of 5Ј Hoxd genes in a posterodistal domain, which constitutes the digit presumptive territory. Using a set of deletions and duplications, Kmita et al (2002) showed that, although inactivation of Hoxd13 does not affect the expression pattern of Hoxd12, the deletion of Hoxd13 results in Hoxd12 adopting a Hoxd13 expression pattern. The same holds true for more 3Ј deletions that bring Hoxd11 in the position of Hoxd13, thus giving Hoxd11 a Hoxd13 pattern.…”

“…The same reallocation of Hoxd11 leads to Hoxd11 being expressed as Hoxd13. This finding, however, induces a spectacular polydactyly associated with digit fusions and a delay in ossification (Kmita et al, 2002). This gain-of-function effect of Hoxd11 is explained by another property of the HoxD cluster, namely posterior prevalence, by which a functional suppression is normally exerted by Hoxd13 over Hoxd11 (van der Hoeven et al, 1996;Goff and Tabin, 1997).…”

Evolution of vertebrate appendicular structures: Insight from genetic and palaeontological data

“…The Shh expression subsequently triggers the second phase of 5 0 Hoxd genes regulation (E10.5-E12) distally in the presumptive digit-forming region. Inversion of early collinear expression pattern of five centromeric genes (d9-d13) is the hallmark of a second wave of Hoxd gene expression: Hoxd13 is expressed at the highest level and in a domain that extends most anteriorly (Kmita et al, 2002; (Fig. 4).…”