Studies On Transgenic Mice With Desaturase Enzymes And Developmental Pathway Of Sonic Hedgehog

Microorganisms and higher plants possess their own omega-3and omega-6polyunsaturated fatty acid (PUFAs) biosynthetic pathways. The n-6fatty aciddesaturase gene fad2codes for the n-6desaturase enzyme that coverts oleic acid (OA18:1n-9) into linoleic acid (LA18:2n-6). The n-3fatty acid desaturase gene fat1codes the n-3desaturase enzyme that converts n-6PUFAs into n-3PUFAs. Mammalslack n-3and n-6desaturase enzymes; therefore, they must obtain their omega-3andomega-6fatty acids by consuming plants or seafood. The beneficial effects of n-3andn-6PUFAs on human development and cardiovascular health have been welldocumented. Here, we generated fat1and fad2transgenic mice by introducingmammal expression vectors containing the fat1and fad2genes via microinjection.Seven transgenic mice were obtained that expressed functional n-3and n-6desaturaseenzymes. Analysis of the fatty acid contents of transgenic mouse livers revealed thatn-6and n-3PUFA levels were greatly increased in the transgenic mice compared towild-type mice. The use ratios of n-9PUFAs (18:1n-9) and n-6PUFAs were bothgreater in the transgenic mice than in the wild-type controls. These transgenic micewere capable of producing their own omega-3and omega-6fatty acids. They have thesame fatty acid metabolic pathways as higher plants and microbes.During our research on the transgenic mice, we found that more abnormaldevelopment occurred during animal development in transgenic mice than that in thewild-type mice. So we transfer our attention to the morphogens during animaldevelopment. The morphogens control the process that the initially na ve cells of anembryo reliably organized into the specific structures of an adult organism. Classicexamples of morphogens produced during development, include proteins of Wingless(Wg), Hedgehog (Hh), and Transforming growth factor-β(TGF-β) families.The proteins of the Hedgehog proteins (Sonic Hh, India Hh, and Desert Hh) arepowerful morphogens play a key role in embryonic development, adult stem cellmaintenance, and the aberrant activation of the Hh pathway has been implicated inmany types of cancers. In vertebrates, the function of Sonic Hedgehog (Shh) has been thoroughly characterized. Shh plays a critical role in developmental patterning of thebrain in mice and humans, as the absence of Shh induces holoprosencephaly andcyclopia. Shh also regulates limb development as well as cellular proliferation anddifferentiation in both neuronal and non-neuronal cells. In addition, aberrant Shhexpression is implicated in the biogenesis of an increasing number of human cancers,including medulloblastoma, melanoma, liver, pancreatic, and urogenital tumors.Here we dissect the mechanism of Shh secretion in vivo and vitro. We show thatin polarized epithelial cells, Adam10mediates the basolateral secretion of Shh, andthat Disp1on the producing cells is required for this process. We further show that therange of Shh signaling is increased in Adam10(disintegrin and metalloproteinase)overexpression cells. These findings reveal an unexpected functional link betweenShh lipidation, Disp1, and Adam10and provide a model in which the reiterated Disp1-dependent secretion, coupled to Adam10dependent release, is responsible for thedistribution of Shh through a tissue.