Human transferrin gene expression (Bruno Baron)
Transferrin (Tf), the iron-transport protein of vertebrate serum, is mainly synthesized in hepatocytes but is also found in other cell-types including Sertoli cells and oligodendrocytes (OLs). We have previously found that Tf gene makes use of different combinations of transcriptional factors in different subsets of cells to achieve tissue-specific expression. It has been suggested that the action of Tf in the brain is not only related to the uptake and distribution of iron but is also involved in myelination and OL maturation. Transgenic mice offer the oportunity for a combined molecular, anatomical, physiological and behavioral analysis of the role of Tf in the myelination process. Therefore, we have now generated transgenic mice overexpressing Tf specifically in brain. These animals display an increased expression of some myelin markers (MBP and CNPase). At the ultrastructural level the axons appear healthy and enlarged in size when compared with non transgenic littermates; this last feature may be associated to the increase in the synthesis of myelin components. Furthermore, transgenic mice display a normal behavior and have significantly better motor coordination, probably due to the larger diameters of axons. These results suggest that Tf expression has a direct role in central nervous development and myelin maintenance and may be of value in the treatment of myelin disorders.
Human melanotransferrin gene expression (Nathalie Duchange)
Melanotransferrin is a protein involved in iron metabolism which is overexpressed in human melanomas. Our goal is to understand the regulatory mecanisms involved in the increase of gene expression in tumor cells. We characterized a key role of a NFAT (Nuclear Factor of Activated T cells) complex through an enhancer element and, while screening a melanoma cDNA library for NFAT family members, we isolated several clones coding for double-stranded RNA binding factors of the ILF3 family (Interleudkun Binding Factor 3). These factors had been previously described as components of the NFAT complex and this prompted us to study in detail different ILF3 isoforms. The implication of these factors in melanotransferrin gene expression could not be demonstrated to date and it is possible that the effect, if it exists, might be indirect. However, the description of several alternative splicing events in the ILF3 gene allowed to clarify the structure and diversity of the generated products and will help to understand the properties of these double-stranded RNA binding factors.
The human apolipoprotein A-I/C-III/A-IV gene cluster (Mario M. Zakin)
The apolipoprotein A-I/C-III/A-IV gene cluster is involved in the metabolism and transport of lipids. We have generated transgenic mice expressing the human cluster. These mice provide an interesting model for studies of the regulation of the three genes in combination. They are also useful for studies of the function of the proteins encoded by the three genes. Expression of the human cluster induced hyperlipidemia but reduced atherogenesis in genetically modified mice lacking apolipoprotein E. We have recently demonstrated that the expression of the human gene cluster in mice also protects against atherogenesis in response to a high fat-high cholesterol diet. We have also generated transgenic mice expressing the human apolipoprotein A-IV. This expression reduced atherosclerotic lesions in mice lacking apolipoprotein E, without an increase in HDL cholesterol. The protection observed is accompanied by an in vivo reduction of the oxidation parameters, suggesting that human apolipoprotein A-IV acts in vivo as an antioxidant. Using our transgenic models, we are now analysing the interactions between infection, inflammation and atherosclerosis.