Journal
DEVELOPMENT
Volume 144, Issue 18, Pages 3315-3324Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/dev.149765
Keywords
Tympanic membrane; External auditory meatus; Middle ear; Hoxa2; Chick-quail chimera; Morphological evolution; Mouse
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Funding
- Ministry of Education, Culture, Sports, Science, and Technology of Japan [26460256, 16K15746]
- Takeda Science Foundation, Osaka, Japan
- Japan Society for the Promotion of Science Overseas Research Fellowship
- Swiss National Science Foundation [Schweizerischer Nationalfonds zur Forderung der Wissenschaftlichen Forschung] [31003A_149573]
- Novartis Foundation
- Grants-in-Aid for Scientific Research [16K15746, 17H06385] Funding Source: KAKEN
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We have proposed that independent origins of the tympanic membrane (TM), consisting of the external auditory meatus (EAM) and first pharyngeal pouch, are linked with distinctive middle ear structures in terms of dorsal-ventral patterning of the pharyngeal arches during amniote evolution. However, previous studies have suggested that the first pharyngeal arch (PA1) is crucial for TM formation in both mouse and chick. In this study, we compare TM formation along the anterior-posterior axis in these animals using Hoxa2 expression as a marker of the second pharyngeal arch (PA2). In chick, the EAM begins to invaginate at the surface ectoderm of PA2, not at the first pharyngeal cleft, and the entire TM forms in PA2. Chick-quail chimera that have lost PA2 and duplicated PA1 suggest that TM formation is achieved by developmental interaction between a portion of the EAM and the columella auris in PA2, and that PA1 also contributes to formation of the remaining part of the EAM. By contrast, in mouse, TM formation is highly associated with an interdependent relationship between the EAM and tympanic ring in PA1.
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