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Mechanisms of Mammalian Middle Ear Ossicle Transition from the Reptilian Jaw Joint
Author(s) -
Urban Daniel,
Sears Karen
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.345.3
Subject(s) - middle ear , biology , malleus , ossicles , inner ear , anatomy , incus , stapes , cochlea , evolutionary biology , neuroscience
During synapsid evolution, postdentary elements in the reptilian jaw transitioned into the middle ear of early mammals. Separation from the dentary allowed unconstrained evolution of the middle ear ossicles, resulting in increased hearing sensitivity and amplified frequency range. Given the importance of such an innovation, it is essential to understand the evolutionary pathway that led to the current phenotype, as this has implications for understanding the development of all mammals. Using an extant model system, Monodelphis domestica , we investigate the developmental basis of the definitive mammalian middle ear. We utilize micro‐CT imaging to characterize the morphological events underpinning the transition, cryosectioning and immunohistochemistry to identify cellular processes behind the morphological events, and laser capture microscopy followed by RNA Sequencing to identify changes in gene expression driving the cellular processes. Among our findings are: decreasing size and rearward movement of the middle ear ossicles appear to be false illusions created by the continued growth and expansion of the surrounding skull elements; separation of Meckel's cartilage from the malleus, occurring at postnatal day 20, is facilitated by apoptosis and is a prerequisite for the onset of hearing; separation and functional changes are due to alterations in timing and expression levels of key genes. Supported by NSF Graduate Research Fellowship and Doctoral Dissertation Improvement Grant.