Are birds pseudoteeth and denticulations related to touch papilla? An investigation in parrot, goose, and chicken

• Published in: Morphologie 2023-06, Vol.107 (357), p.238-251
• Main Authors: Louryan, S., Choa-Duterre, M., Lejong, M., Vanmuylder, N.
• Format: Article
• Language: English
• Subjects: Animals; Bill tip organ; BMP4; Bone and Bones; Chicken; Chickens; Denticulations; Geese; Goose; Parrot; Parrots; PAX9; PITX2; Pseudoteeth; Sensory corpuscles; SHH; Touch; Touch papillae
• ISSN: 1286-0115
• DOI: 10.1016/j.morpho.2022.11.002

•We elucidate the goose denticulations development, and the structure of adult parrot pseudoteeth remnants (their development was already described in a previous contribution).•We demonstrate that all kinds of pseudoteeth and denticulations contain numerous touch organs, and that there is no fundamental difference between pseudoteeth and bill tip organ. We observe in the chicken embryo some primordia suggesting abort pseudoteeth development. We first studied the morphology and the development of goose denticulations, which develop mainly by a ripple process, and the touch papillae of the bill tip organ, which appears through an evagination process at the end of the beak. During their development, we observed the specific expression of PAX9, PITX2, and BMP4, while SHH was expressed mainly in the basal layer of the epithelium in a non-specific manner. Adult goose denticulations are associated with numerous columns. The goose denticulations and columns were filled with numerous Herbst and Grandry corpuscles, as well the touch papillae of the bill tip organ. Histological analysis of adult parrot pseudoteeth revealed that the osseous pseudoteeth were extended by similar columns filled with Herbst and Grandry corpuscles. We also examined adult and embryonic chicken beaks. During ontogeny, we observed a process of rostral evagination with folding associated with discrete ripples in the anterior part of the beak rudiment, in which PAX9, PITX2, and BMP4 are expressed. In the corresponding adult areas, there were numerous sensory corpuscles with rostral columns, which were similar to the features observed in goose. These observations support the hypothesis that pseudoteeth and denticulations constitute sensory organs, and that the touch papillae exhibit some similarities with pseudoteeth.