Retinoic acid-induced developmental defects are mediated by RARβ/RXR heterodimers in the pharyngeal endoderm

Abstract

Fusion and hypoplasia of the first two branchial arches, a defect typically observed in retinoic acid (RA) embryopathy, is generated in cultured mouse embryos upon treatment with BMS453, a synthetic compound that exhibits retinoic acid receptor β (RARβ) agonistic properties in transfected cells. By contrast, no branchial arch defects are observed following treatment with synthetic retinoids that exhibit RARα or RARγ agonistic properties. The BMS453-induced branchial arch defects are mediated through RAR activation, as they are similar to those generated by a selective pan-RAR agonist, are prevented by a selective pan-RAR antagonist and cannot be mimicked by exposure to a pan-RXR agonist alone. They are enhanced in the presence of a pan-RXR agonist, and cannot be generated in Rarb-null embryos. Furthermore, they are accompanied, in the morphologically altered region, by ectopic expression of Rarb and of several other direct RA target genes. Therefore, craniofacial abnormalities characteristic of the RA embryopathy are mediated through ectopic activation of RARβ/RXR heterodimers, in which the ligand-dependent activity of RXR is subordinated to that of RARβ. Endodermal cells lining the first two branchial arches respond to treatment with the RARβ agonist, in contrast to neural crest cells and ectoderm, which suggests that a faulty endodermal regionalization is directly responsible for RA-induced branchial arch dysmorphologies. Additionally, we provide the first in vivo evidence that the synthetic RARβ agonist BMS453 exhibits an antagonistic activity on the two other RAR isotypes.

21st Century neontology and the comparative development of the vertebrate skull

“…Conversely, ectopic RA (or RAR agonists) has significant effects on the anterior ectodermal development, including on anterior endodermalectodermal contacts (e.g., Lee et al, 1995;Kuratani et al, 1998;Escriva et al, 2002;Matt et al, 2003). Matt et al (2003) showed that by using a RAR␤ specific agonist the BA defects associated with RA tetratogenesis were largely replicated; they also applied the agonist to mice carrying a RA-responsive element (RARE) that normally gives expression only up to the second pharyngeal pouch and found reporter expression throughout the APE.…”

“…Matt et al (2003) showed that by using a RAR␤ specific agonist the BA defects associated with RA tetratogenesis were largely replicated; they also applied the agonist to mice carrying a RA-responsive element (RARE) that normally gives expression only up to the second pharyngeal pouch and found reporter expression throughout the APE. Thus, the lack of proper anterior endodermal-ectodermal contacts and development were correlated with abnormal, anterior RA signaling.…”

Fate of retinoic acid–activated embryonic cell lineages

“…The rationale for these studies is that most, if not all, tissues express at least one of the RARs (Dolle, 2009 for a review), that should activate the reporter upon binding of endogenous RA. The RARE-hsp68-lacZ transgene has been widely used in subsequent studies (e.g., Malpel et al, 2000;Mic et al, 2002;Niederreither et al, 2002b;Fan et al, 2003;Matt et al, 2003Matt et al, , 2005Yashiro et al, 2004;Sirbu et al, 2005;Molotkov et al, 2006;Sirbu and Duester, 2006;Ribes et al, 2009;Zhao et al, 2009). Three lines of evidence have validated this transgene as a reliable indicator of RA activity: (1) there is a close match between the patterns of lacZ activity and the expression patterns of RA-synthesizing enzymes (Rdh10, Raldhs) at early embryonic stages, (2) activity of the lacZ reporter is severely down-regulated in knockout mice for the above enzymes (Niederreither et al, 1999;Mic et al, 2002;Matt et al, 2005;Molotkov et al, 2006;Sandell et al, 2007), (3) on the other hand, the reporter is almost ubiquitously activated within 6 h after administration of a bolus dose of RA to the pregnant mothers (Rossant et al, 1991), and is ectopically activated when RA-metabolizing enzymes are absent Sakai et al, 2001;Uehara et al, 2009).…”

Retinoic acid down‐regulates Tbx1 expression in vivo and in vitro

“…Experimental manipulation of retinoid receptor signaling also produces phenocopies of DGS; compound inactivation of RA receptors RAR␣ and RAR␤ (Lohnes et al, 1994;Mendelsohn et al, 1994;Ghyselinck et al, 1998;Dupe et al, 1999), retinoid X receptor RXR␣ and RARs ␣, ␤, and ␥ (Kastner et al, 1997), and chemical alteration with a either a pan-RAR antagonist (Wendling et al, 2000) or an RAR␤ agonist (Matt et al, 2003) all display phenotypes where development of the pharyngeal region is disrupted.…”