Ift88 is involved in mandibular development

Abstract

The mandible is a crucial organ in both clinical and biological fields due to the high frequency of congenital anomalies and the significant morphological changes during evolution. Primary cilia play a critical role in many biological processes, including the determination of left/right axis patterning, the regulation of signaling pathways, and the formation of bone and cartilage. Perturbations in the function of primary cilia are known to cause a wide spectrum of human diseases: the ciliopathies. Craniofacial dysmorphologies, including mandibular deformity, are often seen in patients with ciliopathies. Mandibular development is characterized by chondrogenesis and osteogenesis; however, the role of primary cilia in mandibular development is not fully understood. To address this question, we generated mice with mesenchymal deletions of the ciliary protein, Ift88 (Ift88^fl/fl ;Wnt1Cre). Ift88^fl/fl ;Wnt1Cre mice showed ectopic mandibular bone formation, whereas Ift88 mutant mandible was slightly shortened. Meckel's cartilage was modestly expanded in Ift88^fl/fl ;Wnt1Cre mice. The downregulation of Hh signaling was found in most of the mesenchyme of Ift88 mutant mandible. However, mice with a mesenchymal deletion of an essential molecule for Hh signaling activity, Smo (Smo^fl/fl ;Wnt1Cre), showed only ectopic mandibular formation, whereas Smo mutant mandible was significantly shortened. Ift88 is thus involved in chondrogenesis and osteogenesis during mandibular development, partially through regulating Sonic hedgehog (Shh) signaling.

Keywords: Hedgehog signaling; Ift88; Meckel's cartilage; mandibular bone.

Figure 1

Mandibular bone phenotypes in Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice. Oral (A–F), aboral (G–I), buccal (M–O) and lingual (P–R) view of skeletal preparation of wild‐type, Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice at E18.5. (J–L) Proximal end of skeletal preparation of wild‐type, Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice at E18.5. Green arrows and arrowheads indicate extra cartilage formation and ectopic mandibular bone formation, respectively. Scale bars: 1 mm.

Figure 2

Histological mandibular bone phenotypes in Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice. Frontal sections show the developing mandibular bone in wild‐type, Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice at E18.5. Blue arrow and arrowheads indicate wild‐type endogenous lingual mandibular bone and mutant excess mandibular bone, respectively. Green arrow indicates the gap between lingual and buccal bone. Yellow arrow indicate the thin bone between lingual and buccal bone. Scale bars: 500 μm (A–F), 250 μm (G–I).

Figure 3

Meckel's cartilage in Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice. 3D reconstruction of Meckel's cartilage of wild‐type, Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice at E14.5.

Figure 4

Initiation of mandibular bone formation. (A–C) Oral view of whole mount showing Runx2 expression. (D–F) Frontal sections showing in situ hybridization of Runx2. Arrowheads and arrows indicate endogenous and ectopic mandibular bone region, respectively. Scale bars: 500 μm.

Figure 5

Shh signaling in mandibles in Ift88 ^fl/fl ;Wnt1Cre and Smo ^fl/fl ;Wnt1Cre mice. Frontal sections show in situ hybridization of Ptch1 (A,C–F,K) and Gli1 (B,G–J,L) in the anterior (C,D,G,H) and middle (molar) region (A,B,E,F,I–L) of wild‐type (A,B,C,E,G,I), Ift88 ^fl/fl ;Wnt1Cre (D,F,H,J) and Smo ^fl/fl ;Wnt1Cre (K, L) mice at E11.5 (A, B) and E12.5 (C–L). Meckel's cartilage is outlined by red dots. Scale bars: 250 μm.