Fig. 5. Phenotypes of Ednra and Ednrb knock-in mice. (A) RMCE-mediated knock-in of Ednra and Ednrb cDNA into the Ednra locus. Partial structures of the wild-type and knocked-in Ednra allele and RT-PCR analysis for the expression of knocked-in genes in mandibular arches of E9.5 Ednra- and Ednrb-knock-in heterozygous embryos are shown. PCR primers were represented by arrowheads in the left panel. Note that 753- and 659-bp bands correspond to knocked-in and endogenous Ednra transcripts, respectively. (B-H) Facial appearances (B,C) and skeletal structures (D-H) of E18.5 Ednra^lacZ/A (Ednra-knock-in) (B,D) and Ednra^lacZ/B (Ednrb-knock-in) (C,E-H) mice. Ednra knock-in restored normal facial appearance (B) and skeletal structures (D). Ednrb knock-in mice still exhibit craniofacial defects resembling the Ednra-null phenotype (C,E), except for some differences described below. White arrowhead, ectopic cartilage connecting the incus and extended basitrabecular process. (F) Comparison of the morphology of incisive alveolar bones (boxed with dotted line) among the Ednra-null (Ednra^neo/neo), Ednrb-knock-in (Ednra^lacZ/B) and wild-type (Ednra^+/+) mandible. Incisors were removed. The Ednra^lacZ/B incisive alveolus is well developed, comparable with the wild-type one. (G) A representative of the Ednra^B/B hyoid, which is, unlike the Ednra-null hyoid, not fused to the basisphenoid. The body has an extended ossification center and is connected to the stapes though a transformed lesser horn. The great horn is fused with the superior horn of the thyroid (arrow). (H) Ectopic cartilage (arrowhead) between the malleal/incal region and ala temporalis in Ednra^lacZ/B mice. at, ala temporalis; bh, body of hyoid; bs, basisphenoid; dnt, dentary; fovl, fenestra ovalis; ghh, greater horn of hyoid; hy, hyoid; in, incus; jg, jugal; lhh, lesser horn of hyoid; LI, lower incisor; ma, malleus; mx, maxilla; pmx, premaxilla, sp, styloid process; st, stapes; zpmx, zygomatic process of maxilla; ^*, ectopic structure.