Essential Role of Nr2f Nuclear Receptors in Patterning the Vertebrate Upper Jaw

Abstract

The jaw is central to the extensive variety of feeding and predatory behaviors across vertebrates. The bones of the lower but not upper jaw form around an early-developing cartilage template. Whereas Endothelin1 patterns the lower jaw, the factors that specify upper-jaw morphology remain elusive. Here, we identify Nuclear Receptor 2f genes (Nr2fs) as enriched in and required for upper-jaw formation in zebrafish. Combinatorial loss of Nr2fs transforms maxillary components of the upper jaw into lower-jaw-like structures. Conversely, nr2f5 misexpression disrupts lower-jaw development. Genome-wide analyses reveal that Nr2fs repress mandibular gene expression and early chondrogenesis in maxillary precursors. Rescue of lower-jaw defects in endothelin1 mutants by reducing Nr2f dosage further demonstrates that Nr2f expression must be suppressed for normal lower-jaw development. We propose that Nr2fs shape the upper jaw by protecting maxillary progenitors from early chondrogenesis, thus preserving cells for later osteogenesis.

Evolution and development of the fish jaw skeleton

“…In zebrafish, dorsal–ventral patterning is controlled by ventral expression of edn1, hand2, dlx, jag1b, notch2 , and Nr2f factors (see more detailed discussion later; Alexander et al, ; Barske et al, , ; C. T. Miller, Schilling, Lee, Parker, & Kimmel, ; C. T. Miller, Yelon, Stainier, & Kimmel, ; Talbot, Johnson, & Kimmel, ; Zuniga, Stellabotte, & Crump, ). Mice also require Edn1, Hand2 , and Dlx factors for correct dorsal–ventral jaw patterning, and Jagged1‐Notch2 signaling is involved in patterning of the mouse stapes and incus (homologous to the hyomandibula and palatoquadrate, respectively) (Beverdam et al, ; Depew, Lufkin, & Rubenstein, ; Ozeki et al, ; Teng et al, ).…”

“…Notch2 represses dlx3b , dlx5a , and dlx6a expression to repress intermediate and ventral patterning, and positively regulates hey1 to promote dorsal identity (Figure b; Zuniga et al, ). Jagged1b‐Notch2 signaling in the dorsal arch is interpreted to inhibit cartilage formation, whereas ventral edn1 is proposed to promote cartilage formation (Barske et al, , ). During early development of the arches, ventral edn1 expression is induced by bmps , which also repress jag1b dorsally to ensure specification of the ventral and intermediate domains of the jaw (Alexander et al, ).…”

“…First arch jaw joint patterning requires balance between edn1 which induces nkx3.2 , and activity of barx1 and hand2 to correctly position the joint, prevent ectopic joints, and promote cartilage formation (R. F. Miller, Cloutier, et al, ; C. T. Miller, Yelon, et al, ; Nichols et al, ). Promotion of dermal bone formation in the dorsal portion of arches and inhibition of chondrogenesis is regulated by Jagged1b‐Notch2 and Nr2f signaling, whereas ventral cartilage formation is positively induced by edn1 (Barske et al, , ).…”

Transcriptomics reveals complex kinetics of dorsal–ventral patterning gene expression in the mandibular arch

“…Homeotic transformations along the D–V axis are also observed in Dlx5/6 and Hand2 mutant embryos (Barron et al, ; Beverdam et al, ; Depew, Lufkin, & Rubenstein, ; Miller, Schilling, Lee, Parker, & Kimmel, ; Talbot, Johnson, & Kimmel, ; Walker, Miller, Coffin Talbot, Stock, & Kimmel, ; Yanagisawa, Clouthier, Richardson, Charité, & Olson, ). In contrast, overexpression of Edn1 in the dorsal arch (zebrafish) or maxillary prominence (mouse) or loss of Nr2f leads to the upregulation of ventral gene expression and subsequent homeotic transformation of maxillary into more mandibular‐like structures (Alexander et al, ; Barske et al, ; Tavares & Clouthier, ; Zuniga, Rippen, Alexander, Schilling, & Crump, ). Bmps also act as morphogens during mandibular arch development, inducing Hand2 expression, at least in zebrafish (Alexander et al, ; Zuniga et al, ).…”

“…Edn1 acts as a permissive morphogen, required for the initiation of a mandibular arch-specific gene expression cascade that includes Hand and Dlx genes (Clouthier et al, 2000(Clouthier et al, , 2010Miller, Schilling, Lee, Parker, & Kimmel, 2000;Nair, Li, Cornell, & Schilling, 2007). This occurs, at least in part, through the negative regulation of Nr2f family members, which repress expression of genes associated with ventral mandibular development (Barske et al, 2018). Absence of Edn1 results in a change in D-V identity, with the resulting structures resembling more maxillary-like structures.…”