Analysis of two distinct retinoic acid response elements in the homeobox gene Hoxb1 in transgenic mice

Abstract

Expression of vertebrate Hox genes is regulated by retinoids such as retinoic acid (RA) in cell culture and in early embryonic development. Retinoic acid response elements (RAREs) have been identified in Hox gene regulatory regions, suggesting that endogenous retinoids may be involved in the direct control of Hox gene patterning functions. Previously, two RAREs located 3' of the murine Hoxb1 gene, a DR(2) RARE and a DR(5) RARE, have been shown to regulate Hoxb1 mRNA expression in the neural epithelium and the foregut region, respectively; the foregut develops into the esophagus, liver, pancreas, lungs, and stomach. We have now examined the functional roles of these two types of 3' RAREs in regulating Hoxb1 expression at different stages of gestation, from embryonic day 7.5 to 13.5, in transgenic mice carrying specific RARE mutations. We demonstrate that the DR(5) RARE is required for the regulation of Hoxb-1 transgene region-specific expression in the gut and extraembryonic tissues, as well as for the RA-induced anteriorization of Hoxb-1 transgene expression in the gut. In contrast, expression of the Hoxb1 transgene in the neural epithelium requires only the DR(2) RARE. By in situ hybridization, we have identified a new site of Hoxb1 expression in the developing forelimbs at approximately day 12.5, and we show that, in transgenic embryos, expression in the forelimb buds requires that either the DR(2) or the DR(5) RARE is functional. Attainment of a high level of Hoxb1 transgene expression in other regions, such as in rhombomere 4 (r4) and in the somites, requires that both the DR(2) and DR(5) RAREs are functional. In addition, our transgenic data indicate that the Hoxb1 gene is expressed in other tissues such as the hernia gut, genital eminence, and lung. Our analysis shows that endogenous retinoids act through individual DR(2) and DR(5) RAREs to regulate Hoxb1 expression in different regions of the embryo and that functional redundancy between these DR(2) and DR(5) RAREs does not exist with respect to neural epithelium and the gut Hoxb1 expression.

Antero-posterior patterning of the vertebrate digestive tract: 40 years after Nicole Le Douarin's PhD thesis

“…In each of these cases it is unclear if RA is acting directly upon the endoderm, or indirectly via the mesoderm. The best evidence for direct action of RA upon the endoderm has been provided by investigating the Hoxb1 promoter, which is regulated by RA in endoderm and ectoderm through two different promoter elements (Huang, et al, 2002;Huang, et al, 1998). No such elements have been identified in the Pdx1 or CdxA/1 promoters.…”

Multiple points of interaction between retinoic acid and FGF signaling during embryonic axis formation

“…However, those experiments do not rule out the possibility that RAR signaling directly regulates the expression of HOXB9 and perhaps other HOX genes. Several known and putative retinoic acid response elements have been identified in HOX genes (Dupe et al, 1997;Huang et al, 2002;Huang et al, 1998;Marshall et al, 1994;Ogura and Evans, 1995a;Zhang et al, 1997) suggesting that RAR may act in concert with XCAD3 and perhaps other factors, instead of acting upstream of XCAD3 within a strict hierarchy. Therefore, we examined this possibility by co-injecting the RAR-MO together with XCAD3 mRNA.…”

Induction of HoxB Transcription by Retinoic Acid Requires Actin Polymerization

“…Several lines of evidence have demonstrated the importance of RA receptors (RARs) for patterning and basal expression of Hox genes in the vertebrate neural tube (Marshall et al, 1994(Marshall et al, , 1996Gould et al, 1998;Dupe et al, 1999). However, expression of anterior HoxB genes also depends on an auto-regulatory circuit involving the HoxB1 protein and the Prep1-Pbx1 complex (Marshall et al, 1996;Maconochie et al, 1997;Dupe et al, 1999;Jacobs et al, 1999;Ryoo et al, 1999;Ferretti et al, 2000Ferretti et al, , 2005Huang et al, 2002). Prep1 and Pbx1 are essential genes in embryonic development (Selleri et al, 2001;Waskiewicz et al, 2002;Deflorian et al, 2004;Penkov et al, 2005;Ferretti et al, 2006;Di Rosa et al, 2007).…”

“…Unlike monomeric Prep1 and Pbx1, dimeric Prep1-Pbx1 complexes bind DNA and interact with HoxB1 to activate HoxB1 and HoxB2 transcription This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E09 -02-0114) on May 28, 2009. (Berthelsen et al, 1998;Ryoo et al, 1999;Ferretti et al, 2000Ferretti et al, , 2005Huang et al, 2002).…”