Additional enhancer copies, with intact cdx binding sites, anteriorize Hoxa-7/lacZ expression in mouse embryos: evidence in keeping with an instructional cdx gradient

Abstract

Expression of a Hoxa-7/lacZ reporter construct in transgenic mouse embryos is shifted anteriorly when the upstream enhancer is multimerized. The shift occurs in spinal ganglia, neurectoderm and in both paraxial and lateral plate mesoderms. Much of the multimer effect is inhibited by destruction of a single caudal (cdx) binding motif in the additional copies of the enhancer. These observations are in agreement with earlier enhancer multimerization analyses made for Hoxb-8 (Charité et al., 1998). Our findings therefore provide further evidence that the anterior limit of a Hox gene's expression domain is normally dependent upon and is determined by, the dosage of transcription factor(s) which bind to its enhancer element(s) and that these factors may be, or must include, the cdx proteins. We consider these findings in terms of both instructional (morphogen-like) gradient and timing models for the establishment of Hox gene expression domains. Enhancer multimerization results in an earlier onset of Hoxa-7/lacZ activity in the embryo. In neurectoderm at 8.7 days and in mesoderm at 10.5 days, the anterior boundaries of expression are located posterior to those seen at some earlier stages of development. We discuss how these findings are in keeping with a model where Hox expression boundaries become set along instructional cdx gradients, formed by cdx decay in cells moving away from the primitive streak region.

Epigenetic regulations in hematopoietic Hox code

“…Similarly, the transcriptional stimulation of the Hox genes by Cdx proteins occurs at the Cdx-binding sites (TTTATG), which are often found in clusters throughout the Hox complexes (Gaunt et al, 2004;Tabaries et al, 2005). Two Cdx4-binding sites have been identified in the 5 0 regulatory region of mouse Hoxa9 gene: one contains a tandem repeat unit and the other a single Cdx-binding site (Yan et al, 2006a).…”

“…Hox expression boundaries respond to Cdx proteins in a dose-dependent manner, and Cdx gradients might serve as instructional (morphogen) gradients for setting Hox expression patterns. In this model, temporal colinearity and Cdx gradients operate together in the establishment of Hox boundaries (Gaunt et al, 2004(Gaunt et al, , 2008. Cdx protein concentration may regulate the rate and extent of sequential Hox gene activation (temporal colinearity).…”

HOX Gene Regulation in Acute Myeloid Leukemia: CDX Marks the Spot?

“…These include the ability of Cdx proteins to directly bind to Cdx-consensus binding sites found in clusters throughout the Hox complexes. 28,29 In addition, gene targeting studies demonstrate similar homeotic transformations in Cdx1, Cdx2 and Cdx4-deficient mice and zebrafish to those in Hox-deficient animals. [32][33][34][35] Cdx4 and Cdx1 also play a critical role in the specification of hematopoietic stem cells (HSC) from mesoderm in zebrafish, 35,36 and ectopic expression of Cdx4 in murine embryonic stem (ES) cells upregulates a Hox gene expression program and generates increased hematopoietic colony formation following embryoid body differentiation.…”

“…24 Cdx proteins are subsequently expressed during the establishment of the Hox expression domains and stimulate transcription at the Hox gene clusters through direct binding to Cdx-consensus binding sites found in clusters throughout the Hox complexes. 28,29 RA signaling appears to affect Hox gene expression both directly and through Cdx proteins, but it is currently unclear whether the Fgf and Wnt morphogenic signals are transmitted to the Hox genes exclusively through Cdx proteins, or whether Hox genes also respond to these signals independently of Cdx regulation. 24 However, the homeotic transformation of Cdx mutants are similar to Wnt3a and Fgfr1 mutants, suggesting a direct interaction between Wnt and Fgf signaling and the Cdx transcription factors.…”

Synergistic action in P19 pluripotential cells of retinoic acid and Wnt3a on Cdx1 enhancer elements

“…Cdx knockout (Mallo et al, 2009, van den Akker et al, 2002 or over-expression (Gaunt et al, 2008) in mice produces homeotic mutations in vertebrae. The regulation of several mouse Hox genes is known to depend upon Cdx binding motifs in their cis-regulatory elements (Charite et al, 1998, Gaunt et al, 2004. During gastrulation and axial extension, all Cdx genes are expressed in posterior parts of the embryo.…”