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UBC Theses and Dissertations

Characterization of growth and tissue remodelling during the mouse craniofacial and cardiac development Iamaroon, Anak


Craniofacial and cardiac development share many common basic biological processes. Remodelling of the extracellular matrix (ECM) is believed to play an important role during mammalian embryogenesis. But the role of tissue remodelling during morphogenesis of the craniofacial complex and heart remains unclear. Therefore, I hypothesized that changes of basement membrane components and growth factors were associated with remodelling and growth of the embryonic primary palate, the future premaxillary area, and the heart. The present investigation encompassed four projects. First was the characterization of the distribution of major basement membrane components; laminin, type IV collagen and fibronectin; by indirect immunofluorescence in the primary palate as the epithelial seam is disrupted and the mesenchymal bridge forms and enlarges. The results showed that localized disruption of basement membrane components occurred simultaneously with mesenchymal bridge formation and enlargement during primary palate formation. The purposes of the second part were to characterize the distribution patterns of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-a) and their receptor, epidermal growth factor receptor (EGF-R), by immunohistochemistry and to analyze regional patterns of cell proliferation by 5-bromodeoxyuridine (BrdU) incorparation and proliferating cell nuclear antigen (PCNA) immunolocalization during primary palate morphogenesis. The results showed that EGF, TGF-a, and EGF-R were labelled more intensely in the tips and peripheral regions of the facial prominences where cell proliferation was most pronounced. This suggested that EGF and TGF-a stimulate cell proliferation during outgrowth of prominences during primary palate morphogenesis. The purpose of the third part was to look for the presence of enzymes involved in degradation of the basement membrane of the epithelial seam during primary palate morphogenesis. Protein expression of a candidate matrix metalloproteinase (MMP), 72-kDa gelatinase (MMP-2) was studied by indirect immunofluorescence and zymography. The results revealed that MMP-2 was present in the area of fusion in the primary palate and also in the tips and peripheral regions of the facial prominences. This localization of MMP-2 suggested that regional differences in tissue remodelling are involved in directional enlargement of the facial prominences. Gelatin zymography confirmed the presence of active and latent MMP-2 in the developing craniofacial complex. The purpose of the last part was to examine the distribution of MMP-2 and its substrates: type IV collagen, laminin and fibronectin during heart morphogenesis by indirect immunohistochemistry. The results showed that the distribution patterns of MMP-2 were highly correlated with that of the E C M components from embryonic day 9-13. Collectively, these data indicate that the mechanisms of growth and tissue remodelling during craniofacial and heart development are complex and may involve multiple interactions between various molecular factors; including E C M components (type IV collagen, laminin, and fibronectin), growth factors (EGF and TGF-a) and their receptor (EGF-R), and matrix metalloproteinase (MMP-2).

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