Growth Factor Expression In The Rat Condyle - Implications For Craniofacial Development
Introduction The mandible is particularly important in growth and development, in that it contributes to the morphology of the face. From a clinical perspective, mandibular morphologies may be attributed to certain malocclusions. The mandibular condylar cartilage has gained a long-standing interest in orthodontic research, as it is a site of growth and development of the mandible. The initial aim was to extract RNA from the condylar tissue. The main purpose of the experiment was to assess an array of growth factors and to appraise the changes in their regulation, over several time points. Methods This study was carried out in two parts. A pilot study involving 6 rats was used to validate 1) a surgical method for the harvesting the rat condyle; 2) a protocol for the extraction of RNA, following cryogenic grinding of the condyle; and 3) using haematoxylin and eosin and toluidine blue stains, different developmentally distinct time points were identified. In the main study, using 36 rats, 72 condyles were extracted from 4, 10, 21 and 90 day rats and processed through the validated RNA extraction protocol. The remaining eight condyles were assigned for further histological analysis. The level of mRNA obtained and the gene expression for 28 growth factor genes were measured. Quantitative polymerase chain reaction (qPCR) technique was used to compare the relative gene expression at the time points identified. Results The condylar tissue harvesting technique, the cryogenic grinding protocol and RNA extraction methods were all successfully carried out. In all the samples, all growth factor genes investigated were expressed. Across all time points and relative to the three internal normalisation genes, there was subtle up and down regulation of genes involved in chondrogenesis and osteogenesis. However, the recommended two-fold change was not apparent for any of these growth factor genes (-3.85 ≤ fold change ≤ 1.65; p ≥ 0.07). Conclusions The present study showed that the cryogenic grinding protocol was a valid technique in extracting RNA from the condyles and that all the growth factors selected were present in the gene analysis. However, in the rat model, the twofold change in the regulation did not occur for any of the growth factors investigated at any time point selected. However, the potential for the adopted technique for future research directions is well demonstrated.
Advisor: Farella, Mauro; Milne, Trudy; Cannon, Richard
Degree Name: Doctor of Clinical Dentistry
Degree Discipline: Oral Sciences - Discpline of Orthodontics
Publisher: University of Otago
Keywords: growth; factors; rats; condyle; condylar; cartilage; mandible; qPCR; histology
Research Type: Thesis