Date on Master's Thesis/Doctoral Dissertation

12-2017

Document Type

Master's Thesis

Degree Name

M.S.

Department

Oral Biology

Degree Program

Oral Biology, MS

Committee Chair

Sandell, Lisa

Committee Member

Liang, Shuang

Committee Member

Ding, Jiaxing

Committee Member

Running, Mark

Author's Keywords

RDH10; cleft secondary palate; retinoic acid; mouse

Abstract

The focus of this project is to understand the role of Retinoic Acid (RA) produced by RDH10-mediated metabolism of Vitamin A in palate development. For 80 years now, we have known that dietary restriction of RA/Vitamin A can cause cleft palate but we have failed to understand how RA deficiency causes cleft palate. Our gap in knowledge about how RA deficiency causes cleft palate is mainly owing to the fact that we lack a model system to study such defects. The aim of this thesis research project was to determine if conditional inactivation of the Vitamin A metabolic gene Rdh10 in mouse could serve as an experimental model system to study the etiology of RA deficient cleft palate in mammals. This study examined a mouse model system in which Rdh10 was conditionally inactivated using a Tamoxifen-inducible cre-lox system. At embryonic age 16.5 (E16.5), when palate fusion was complete in control embryos, we observed 44% of the Rdh10 conditional mutant embryos had complete cleft of the secondary palate. Histological analysis at E12.5 revealed defects in palate shelf morphology in mutant embryos. Defects at this stage included reduced palate shelf outgrowth and a lack of groove between the shelf and the body of the maxilla. We used a BrdU assay to label proliferating cells, and identified an increase in cell proliferation at the bend region in the mutant embryos compared to controls. Using a reporter mouse strain to detect RA signaling we observed RA signaling within the anterior palate shelf tissues. In order to understand if the cleft palate seen in Rdh10 mutant embryos was due to defects intrinsic to the palate or if the clefts were secondary to abnormalities in development of the mandible or tongue, we isolated and cultured maxilla from control and mutant embryos. We observed that there was no significant difference in fusion rate of palate shelves between control and mutant maxillae cultured ex vivo. In summary, these data demonstrate conditional inactivation of Rdh10 in mice proves to be an effective experimental model system to study how deficiency of RA causes cleft palate. Our findings indicate that RA signaling is active in palate tissue and regulates cell proliferation and palate shelf morphology. However, we find that the primary defect causing cleft palate in RA deficient embryos is not intrinsic to the maxilla. This study opens the door for future investigation to how RA deficiency cause cleft palate by mechanisms extrinsic to the maxilla.

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