Analysis of Sphingosine-1-phosphate signaling mutants reveals endodermal requirements for the growth but not dorsoventral patterning of jaw skeletal precursors

Eli and Edythe Broad Institute for Regenerative Medicine and Stem Cell Research, Department of Cell and Neurobiology, University of Southern California Keck School of Medicine, Los Angeles, CA 90033, USA.
Developmental Biology (Impact Factor: 3.55). 12/2011; 362(2):230-41. DOI: 10.1016/j.ydbio.2011.12.010
Source: PubMed


Development of the head skeleton involves reciprocal interactions between cranial neural crest cells (CNCCs) and the surrounding pharyngeal endoderm and ectoderm. Whereas elegant experiments in avians have shown a prominent role for the endoderm in facial skeleton development, the relative functions of the endoderm in growth versus regional identity of skeletal precursors have remained unclear. Here we describe novel craniofacial defects in zebrafish harboring mutations in the Sphingosine-1-phospate (S1P) type 2 receptor (s1pr2) or the S1P transporter Spinster 2 (spns2), and we show that S1P signaling functions in the endoderm for the proper growth and positioning of the jaw skeleton. Surprisingly, analysis of s1pr2 and spns2 mutants, as well as sox32 mutants that completely lack endoderm, reveals that the dorsal-ventral (DV) patterning of jaw skeletal precursors is largely unaffected even in the absence of endoderm. Instead, we observe reductions in the ectodermal expression of Fibroblast growth factor 8a (Fgf8a), and transgenic misexpression of Shha restores fgf8a expression and partially rescues the growth and differentiation of jaw skeletal precursors. Hence, we propose that the S1P-dependent anterior foregut endoderm functions primarily through Shh to regulate the growth but not DV patterning of zebrafish jaw precursors.

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Available from: Bartosz Balczerski
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    • "On the other hand, the number and morphology of the ceratobranchial arch were relatively normal. The pharyngeal defects are consistent with a recent report that demonstrated morphological defects of the lower jaw in both s1pr2 and spns2 mutants (Balczerski et al., 2012). We also found that the cell adhesion molecule Fig. 1. "
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    ABSTRACT: The lipid mediator sphingosine-1-phosphate (S1P) is a regulator of cardiac development in zebrafish, as disruption of its receptor s1pr2 or transporter spns2 causes migration defects in cardiac progenitors. To examine the genetic interaction of S1P signaling and the cell adhesion molecule fibronectin, we have established a fn;spns2 double mutant. Cardiac migration defects in fn;spns2 mutants were more severe than those in fn or spns2 mutants. We further found that the lower jaw morphology was disorganized in the fn;spns2 mutant, while it had a slightly shortened anterior-posterior distance in the ventral pharyngeal arch in fn and spns2 mutants relative to wild type. Knockdown of fn in the s1pr2 mutant, but not in the s1pr1 mutant, resulted in severe defects in cardiac migration and ventral pharyngeal arch arrangement. Further, in the background of the fn mutant, knockdown of endothelin receptor A (ednra), which was downregulated in the spns2 mutant, caused pharyngeal defects resembling those in the fn;spns2 mutant. These results strongly suggest that Spns2-S1PR2 signaling and fibronectin cooperatively regulate both cardiac and lower jaw development in zebrafish.
    Full-text · Article · Aug 2013 · Biology Open
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    • "In zebrafish, satb2 is most strongly expressed in neural crest cells in the medial region of the arch that are in close proximity to the pharyngeal endoderm, a source of both Bmp and Hh signaling [8], [12], [53], [54]. To determine if the endoderm is necessary for satb2 expression, we analyzed sox32 mutants, which lack endoderm [46]. "
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    ABSTRACT: In human, mutation of the transcription factor SATB2 causes severe defects to the palate and jaw. The expression and sequence of SATB2 is highly conserved across vertebrate species, including zebrafish. We sought to understand the regulation of satb2 using the zebrafish model system. Due to the normal expression domains of satb2, we analyzed satb2 expression in mutants with disrupted Hh signaling or defective ventral patterning. While satb2 expression appears independent of Edn1 signaling, appropriate expression requires Shha, Smo, Smad5 and Hand2 function. Transplantation experiments show that neural crest cells receive both Bmp and Hh signaling to induce satb2 expression. Dorsomorphin- and cyclopamine-mediated inhibition of Bmp and Hh signaling, respectively, suggests that proper satb2 expression requires a relatively earlier Bmp signal and a later Hh signal. We propose that Bmp signaling establishes competence for the neural crest to respond to Hh signaling, thus inducing satb2 expression.
    Full-text · Article · Mar 2013 · PLoS ONE
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    • "Thus, in addition to early dorso-ventral patterning, BMP signaling is required at later stages for differentiation of all the pharyngeal chondrocytes. Similarly, Shh signaling from pharyngeal endoderm was recently shown to be required before 24 hpf for the selective growth and/or differentiation of anterior cranial cartilage precursor cells, without affecting dorso-ventral patterning, by inducing fgf8a expression in oral ectoderm [76]. Ectopic Shha expression by transgenesis in cas mutant embryos restored fgf8a expression and formation of the mandibular and hyoid arches. "
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    ABSTRACT: The cartilaginous elements forming the pharyngeal arches of the zebrafish derive from cranial neural crest cells. Their proper differentiation and patterning are regulated by reciprocal interactions between neural crest cells and surrounding endodermal, ectodermal and mesodermal tissues. In this study, we show that the endodermal factors Runx3 and Sox9b form a regulatory cascade with Egr1 resulting in transcriptional repression of the fsta gene, encoding a BMP antagonist, in pharyngeal endoderm. Using a transgenic line expressing a dominant negative BMP receptor or a specific BMP inhibitor (dorsomorphin), we show that BMP signaling is indeed required around 30 hpf in the neural crest cells to allow cell differentiation and proper pharyngeal cartilage formation. Runx3, Egr1, Sox9b and BMP signaling are required for expression of runx2b, one of the key regulator of cranial cartilage maturation and bone formation. Finally, we show that egr1 depletion leads to increased expression of fsta and inhibition of BMP signaling in the pharyngeal region. In conclusion, we show that the successive induction of the transcription factors Runx3, Egr1 and Sox9b constitutes a regulatory cascade that controls expression of Follistatin A in pharyngeal endoderm, the latter modulating BMP signaling in developing cranial cartilage in zebrafish.
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