Retinoic Acid Promotes Limb Induction through Effects on Body Axis Extension but Is Unnecessary for Limb Patterning

Development and Aging Program, Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
Current biology: CB (Impact Factor: 9.57). 07/2009; 19(12):1050-7. DOI: 10.1016/j.cub.2009.04.059
Source: PubMed


Retinoic acid (RA) is thought to be a key signaling molecule involved in limb bud patterning along the proximodistal or anteroposterior axes functioning through induction of Meis2 and Shh, respectively. Here, we utilize Raldh2-/- and Raldh3-/- mouse embryos lacking RA synthesis to demonstrate that RA signaling is not required for limb expression of Shh and Meis2. We demonstrate that RA action is required outside of the limb field in the body axis during forelimb induction but that RA is unnecessary at later stages when hindlimb budding and patterning occur. We provide evidence for a model of trunk mesodermal RA action in which forelimb induction requires RA repression of Fgf8 in the developing trunk similar to how RA controls somitogenesis and heart development. We demonstrate that pectoral fin development in RA-deficient zebrafish embryos can be rescued by an FGF receptor antagonist SU5402. In addition, embryo ChIP assays demonstrate that RA receptors bind the Fgf8 promoter in vivo. Our findings suggest that RA signaling is not required for limb proximodistal or anteroposterior patterning but that RA inhibition of FGF8 signaling during the early stages of body axis extension provides an environment permissive for induction of forelimb buds.

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Available from: Ovidiu Sirbu, Mar 18, 2014
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    • "For the mouse Aldh1a2 KOs, although the cardiac phenotypes were initially interpreted as supporting the atrial-ventricular patterning model from cardiac morphology, revisiting the analysis of the cardiac defects with additional cardiac progenitor markers revealed that these mutants also display a posterior expansion of the cardiac progenitors (Ryckebusch et al., 2008; Sirbu et al., 2008). Studies initially in zebrafish and later in mice have suggested that the posterior expansion of the cardiac progenitors is potentially at the expense of neighboring forelimbs progenitors (Waxman et al., 2008; Zhao et al., 2009; Sorrell and Waxman, 2011; Cunningham et al., 2013). Despite the genetic data supporting a conserved requirement for RA in restricting cardiomyocyte specification, there are differences in interpretation as to whether or not there is strictly an expansion of the FHF, the earlier differentiating population of cardiomyocytes , and/or the second SHF, a later differentiating population of cardiomyocytes (Ryckebusch et al., 2008; Sirbu et al., 2008). "
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    ABSTRACT: Appropriate levels of retinoic acid (RA) signaling are critical for normal heart development in vertebrates. A fascinating property of RA signaling is the thoroughness by which positive and negative feedback are employed to promote proper embryonic RA levels. In the present short review, we first cover the advancement of hypotheses regarding the impact of RA signaling on cardiac specification. We then discuss our current understanding of RA signaling feedback mechanisms and the implications of recent studies, which have indicated improperly maintained RA signaling feedback can be a contributing factor to developmental malformations. Developmental Dynamics 244:513-523, 2015. © 2014 Wiley Periodicals, Inc.
    Developmental Dynamics 11/2014; 244(3). DOI:10.1002/dvdy.24232 · 2.38 Impact Factor
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    • "Fgf8 expression is initiated upon limb but outgrowth in spite of the inhibitory role of RA, and the simulations predict that receptor binding limits diffusion of RA from the flank initially, once RA signalling enhances the expression of RA receptors, as indeed observed in experiments (Noji et al., 1991; Tabin, 1991). According to the model, receptor saturation eventually permits RA to diffuse further distally and to form a gradient that could regulate aspects of proximal-distal limb bud development (Figure 4C) and that could define the proximal part (stylopod -> humerus) of the proximal-distal axis as suggested by two recent studies (Cooper et al., 2011a; Roselló-Díez et al., 2011) and challenged by the Duester group (Cunningham et al., 2013; Zhao et al., 2009). "
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    ABSTRACT: The mechanism that controls digit formation has long intrigued developmental and theoretical biologists, and many different models and mechanisms have been proposed. Here we review models of limb development with a specific focus on digit and long bone formation. Decades of experiments have revealed the basic signalling circuits that control limb development, and recent advances in imaging and molecular technologies provide us with unprecedented spatial detail and a broader view on the regulatory networks. Computational approaches are important to integrate the available information into a consistent framework that will allow us to achieve a deeper level of understanding and that will help with the future planning and interpretation of complex experiments, paving the way to in silico genetics. Previous models of development had to be focused on very few, simple regulatory interactions. Algorithmic developments and increasing computing power now enable the generation and validation of increasingly realistic models that can be used to test old theories and uncover new mechanisms.
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    • "More specifically, upstream of limb bud outgrowth and Fgf10 expression, Tbx5 and Islet1 (Isl1) are specifically required for initiation of the forelimb and hindlimb buds, respectively (Agarwal et al., 2003; Kawakami et al., 2011; Narkis et al., 2012; Rallis et al., 2003). Furthermore, retinoic acid signaling is required for initiation of forelimb but not hindlimb buds (Cunningham et al., 2013; Zhao et al., 2009). "
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    ABSTRACT: Isl1 expression marks progenitor populations in developing embryos. In this study, we investigated the contribution of Isl1-expressing cells that utilize the ß-catenin pathway to skeletal development. Inactivation of ß-catenin in Isl1-expressing cells caused agenesis of the hindlimb skeleton and absence of the lower jaw (agnathia). In the hindlimb, Isl1-lineages broadly contributed to the mesenchyme, however, deletion of ß-catenin in the Isl1-lineage caused cell death only in a discrete posterior domain of nascent hindlimb bud mesenchyme. We found that the loss of posterior mesenchyme, which gives rise to Shh-expressing posterior organizer tissue, caused loss of posterior gene expression and failure to expand chondrogenic precursor cells, leading to severe truncation of the hindlimb. In facial tissues, Isl1-expressing cells broadly contributed to facial epithelium. We found reduced nuclear ß-catenin accumulation and loss of Fgf8 expression in mandibular epithelium of Isl1(-/-) embryos. Inactivating ß-catenin in Isl1-expressing epithelium caused both loss of epithelial Fgf8 expression and death of mesenchymal cells in the mandibular arch without affecting epithelial proliferation and survival. These results suggest a Isl1->ß-catenin->Fgf8 pathway that regulates mesenchymal survival and development of the lower jaw in the mandibular epithelium. By contrast, activating ß-catenin signaling in Isl1-lineages caused activation of Fgf8 broadly in facial epithelium. Our results provide evidence that, despite its broad contribution to hindlimb mesenchyme and facial epithelium, the Isl1-ß-catenin pathway regulates skeletal development of the hindlimb and lower jaw through discrete populations of cells that give rise to Shh-expressing posterior hindlimb mesenchyme and Fgf8-expressing mandibular epithelium.
    Developmental Biology 01/2014; 387(1). DOI:10.1016/j.ydbio.2014.01.001 · 3.55 Impact Factor
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