Ectopic Meis1 expression in the mouse limb bud alters P-D patterning in a Pbx1-independent manner

Abstract

During limb development, expression of the TALE homeobox transcription factorMeis1 is activated by retinoic acid in the proximal-most limb bud regions, which give rise to the upper forelimb and hindlimb. Early subdivision of the limb bud into proximal Meis-positive and distal Meis-negative domains is necessary for correct proximo-distal (P-D) limb development in the chick, since ectopic Meis1 overexpression abolishes distal limb structures, produces a proximal shift of limb identities along the P-D axis, and proximalizes distal limb cell affinity properties. To determine whether Meis activity is also required for P-D limb specification in mammals, we generated transgenic mice ectopically expressing Meis1 in the distal limb mesenchyme under the control of the Msx2 promoter. Msx2:Meis1 transgenic mice display altered P-D patterning and shifted P-D Hox gene expression domains, similar to those previously described for the chicken. Meis proteins function in cooperation with PBX factors, another TALE homeodomain subfamily. Meis-Pbx interaction is required for nuclear localization of both proteins in cell culture, and is important for their DNA-binding and transactivation efficiency. During limb development, Pbx1 nuclear expression correlates with the Meis expression domain, and Pbx1 has been proposed as the main Meis partner in this context; however, we found that Pbx1 deficiency did not modify the limb phenotype of Msx2:Meis1 mice. Our results indicate a conserved role of Meis activity in P-D specification of the tetrapod limb and suggest that Pbx function in this context is either not required or is provided by partners other than Pbx1.

Meis1 coordinates a network of genes implicated in eye development and microphthalmia

“…For example, together with Pbx1, Meis1 plays a major role as a co-factor for the TFs of the Hox complex, which, in turn, have a pivotal and evolutionarily conserved role in orchestrating embryonic trunk development (Duboule, 2007;Mallo and Alonso, 2013). In accordance with this notion, loss of Meis1 function impairs the formation of Meis1-expressing trunk organs and systems, such as the limbs, heart, blood and vasculature (Azcoitia et al, 2005;Erickson et al, 2010;Hisa et al, 2004;Mercader et al, 1999Mercader et al, , 2009Zhang et al, 2002).…”

Diffusible signals and epigenetic timing cooperate in late proximo-distal limb patterning

“…1) resembles that of Meis1 misexpression in the distal limb bud, namely a distal shift in Hoxa13 activation (Mercader et al, 1999;Mercader et al, 2009). As the mechanisms by which MEIS proteins affect the distal PD transition are unknown, we set out to investigate this shared phenotype.…”

“…At the late limb bud stage, each of the PD segments expresses specific homeobox genes; the stylopod expresses Meis1 and Meis2, the zeugopod Hoxa11 and the autopod Hoxa13 (Mercader et al, 2009;Nelson et al, 1996;Yokouchi et al, 1991). However, the expression of these so-called PD markers is dynamic and sequential during early stages.…”

A unique stylopod patterning mechanism by Shox2 controlled osteogenesis

“…7P). It was reported previously that excessive expression of Pbx (Gordon et al, 2010) or Meis (Mercader et al, 2009) inhibited osteogenesis. Shox2 thus probably functions to antagonize the inhibitory effect of Meis and Pbx for stylopodial skeletogenesis.…”