Expression of Cre recombinase in the developing mouse limb bud driven by a Prxl enhancer

Abstract

We have used a Prx1 limb enhancer to drive expression of Cre Recombinase in transgenic mice. This regulatory element leads to Cre expression throughout the early limb bud mesenchyme and in a subset of craniofacial mesenchyme. Crossing a murine line carrying this transgene to a reporter mouse harboring a floxed Cre-reporter cassette revealed that recombinase activity is first observed in the earliest limb bud at 9.5 dpc. By early to mid bud stages at 10.5 dpc recombination is essentially complete in all mesenchymal cells in the limb. Expression of the Cre recombinase was never detected in the limb bud ectoderm. The use of Prx1-Cre mice should facilitate analysis of gene function in the developing limb.

Two independent modes of chromatin organization revealed by cohesin removal

“…For acute deletion of the floxed exon, we used either a constitutive ubiquitous CRE-driver (Hprt::Cre 43 ), a limb-specific CRE-driver (Prx1::Cre 44 ) or an inducible, liver-specific Cre allele ( Ttr-cre/Esr1 45 .…”

“…The resulting protein lacks the critical HEAT domains conserved in NIPBL/SCC2 proteins. (b–c) E12 embryos (b) and E18 fetuses (c) carrying the conditional Nipbl allele ( Nipbl flox ) and either ubiquitous (Hprt:Cre 43 ) or limb-specific (Prx1::Cre 44 ) Cre recombinase drivers. Structures expressing Cre are rapidly lost in Nipbl flox/flox animals.…”

Msx1 and Msx2 in limb mesenchyme modulate digit number and identity

“…This transgene is known to be expressed later and to a lesser extent in the hindlimb than in the forelimb (Logan et al, 2002; see also the Discussion section). Due to these technical limitations, and because our conditional knockout strategy aimed primarily to decipher the role of Msx genes in the anterior region of the limb, we focused the rest of our study on the analysis of the AP phenotype in the forelimb.…”

“…To investigate Msx function specifically in the limb bud mesoderm, we first combined the conditional floxed allele Msx2 Flox-GFP (hereafter termed Msx2 Flox ) and its deleted form, Msx2 null-GFP (hereafter termed Msx2 null ; Bensoussan et al, 2008), together with the Prx1-Cre deleter transgene (Logan et al, 2002). The latter directs high-level production of Cre in the limb bud mesenchyme, starting as early as 9.5 dpc in the forelimb and 10.5 dpc in the hindlimb.…”

“…To achieve this goal, we made use of the Msx2 Flox-GFP conditional allele we recently described (Bensoussan et al, 2008) and the Prx1-Cre transgene that drives Cre expression specifically in the limb bud mesenchyme (Logan et al, 2002), in conjunction with an Msx1 LacZ null allele (Houzelstein et al, 1997). Analysis of the Prx1-Cre Msx1 Msx2 compound mutants revealed a crucial role for mesodermal expression of Msx1 and Msx2 in specification of digit number and identity along the anteroposterior axis, by means of their involvement in both Shh and BMP signaling pathways.…”