The Function of Protogenin in Craniofacial

• Main Authors: Yu-Chiuan Wang, 王毓權
• Other Authors: Ming-Ji Fann
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/09284884804920670414

博士 === 國立陽明大學 === 神經科學研究所 === 102 === The vertebrate head is a complicated structure composed of bone, cartilage and other connective tissues. This structure evolutionarily emerged with vertebrates around five hundred million years ago. Bones and connective tissues of murine jaws and skulls are derived from cephalic neural crest cells (CNCCs) and paraxial mesoderm cells. Craniofacial skeletons and skull vaults are composed of three major bone parts called membrane bones. Membrane bone is bone that forms directly in membranous connective tissue without previous cartilage formation. It includes (1) frontal bone: the large cranial bone forming the front part of the cranium and includes the upper part of the orbits, (2) parietal bone: either of two skull bones between the frontal and occipital bones that form the top and sides of the cranium, (3) occipital bone: a saucer-shaped membrane bone that forms the back of the skull. Previous studies have indicated that Protogenin (Prtg), an immunoglobulin receptor, is involved in the development of various tissues including the nervous system, the mesoderm and the teeth gemline. To investigate the function of Prtg in vivo, we generated Prtg knock out mice. Here, we report that Prtg deficient mice exhibit impairments of the palatine and skull. Results from lineage tracing experiments, expression patterns of neural crest cell marker genes, and apoptotic assays indicate that the malformation of bones in Prtg deficient mice is due to increased apoptosis of rostral CNCCs. We found that Prtg interacts with Radil and translocates Radil from cytoplasm to cell membrane in cultured cells. Furthermore, Prtg and Radil promote cell motility by increasing expression of activated 51 integrin on cell membrane, which is further enhanced by an application of the Prtg ligand ERdj3. Lower levels of activated 51 integrin are also exhibited on cell membrane of Prtg-deficient rostral CNCCs. These results indicate that ERdj3/Prtg signaling plays a crucial role in the proper migration of a subset of rostral CNCCs and the formation of craniofacial structures by activating the 51 integrin. To further investigate Prtg in neural crest development, we generated PrtgC dominant negative transgenic mice. Upon crossing with Wnt1-Cre mice, the Wnt1-Cre;PrtgC mice exhibit craniofacial defect and with similar penetrance as Prtg-/- mice. Moreover, all of the Wnt1-Cre;PrtgC; Prtg+/- mice show cleft face and die after birth, indicating that Prtg and its interacting protein (possibly the ligand or the cytosolic interacting protein) indeed co-contribute to craniofacial development. A previous study had indicated that Prtg is involved in preventing precocious neuronal differentiation, we used histological analysis and behavioral tests to determine whether there are structural and/or functional defects occurring in the nervous system of Prtg-/- mice. Although the Prtg-/- mice showed some trend towards anti-anxiety behavior, it was not of a significant level and no obvious anatomical defects were identified. In addition to the craniofacial phenotype, we also examined skeletal patterns in Prtg-/- mice and observed the formation of two extra lumbar vertebrae and the transformation of posterior thoracic vertebrae to anterior vertebrae, a phenotype that is similar to mice with mis-expression of Hox genes. The question of whether Prtg regulates expression of Hox genes is under investigation. The contribution of this study is that we are the first laboratory using knock out mouse model to prove the in vivo function of Prtg in mammalian.