mTor, acting mainly via mTORC1, controls dystrophin transcription in a raptor- and rictor-independent mechanism.

There are five members of the RFX family of transcription factors in mammals. While RFX5 plays a well-defined role in the immune system, the functions of RFX1 to RFX4 remain largely unknown. We have generated mice with a deletion of the Rfx3 gene. RFX3-deficient mice exhibit frequent left-right (LR) asymmetry defects leading to a high rate of embryonic lethality and situs inversus in surviving adults. In vertebrates, specification of the LR body axis is controlled by monocilia in the embryonic node, and defects in nodal cilia consequently result in abnormal LR patterning. Consistent with this, Rfx3 is expressed in ciliated cells of the node and RFX3-deficient mice exhibit a pronounced defect in nodal cilia. In contrast to the case for wild-type embryos, for which we document for the first time a twofold increase in the length of nodal cilia during development, the cilia are present but remain markedly stunted in mutant embryos. Finally, we show that RFX3 regulates the expression of D2lic, the mouse orthologue of a Caenorhabditis elegans gene that is implicated in intraflagellar transport, a process required for the assembly and maintenance of cilia. In conclusion, RFX3 is essential for the differentiation of nodal monocilia and hence for LR body axis determination.

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Ciliated ependymal cells play central functions in the control of cerebrospinal fluid homeostasis in the mammalian brain, and defects in their differentiation or ciliated properties can lead to hydrocephalus. Regulatory factor X (RFX) transcription factors regulate genes required for ciliogenesis in the nematode, drosophila and mammals. We show here that Rfx3-deficient mice suffer from hydrocephalus without stenosis of the aqueduct of Sylvius. RFX3 is expressed strongly in the ciliated ependymal cells of the subcommissural organ (SCO), choroid plexuses (CP) and ventricular walls during embryonic and postnatal development. Ultrastructural analysis revealed that the hydrocephalus is associated with a general defect in CP differentiation and with severe agenesis of the SCO. The specialized ependymal cells of the CP show an altered epithelial organization, and the SCO cells lose their characteristic ultrastructural features and adopt aspects more typical of classical ependymal cells. These differentiation defects are associated with changes in the number of cilia, although no obvious ultrastructural defects of these cilia can be observed in adult mice. Moreover, agenesis of the SCO is associated with downregulation of SCO-spondin expression as early as E14.5 of embryonic development. These results demonstrate that RFX3 is necessary for ciliated ependymal cell differentiation in the mouse.

The transcription factor regulatory factor X (RFX)-3 regulates the expression of genes required for the growth and function of cilia. We show here that mouse RFX3 is expressed in developing and mature pancreatic endocrine cells during embryogenesis and in adults. RFX3 expression already is evident in early Ngn3-positive progenitors and is maintained in all major pancreatic endocrine cell lineages throughout their development. Primary cilia of hitherto unknown function present on these cells consequently are reduced in number and severely stunted in Rfx3 Ϫ/Ϫ mice. This ciliary abnormality is associated with a developmental defect leading to a uniquely altered cellular composition of the islets of Langerhans. Just before birth, Rfx3 Ϫ/Ϫ islets contain considerably less insulin-, glucagon-, and ghrelinproducing cells, whereas pancreatic polypeptide-positive cells are markedly increased in number. In adult mice, the defect leads to small and disorganized islets, reduced insulin production, and impaired glucose tolerance. These findings suggest that RFX3 participates in the mechanisms that govern pancreatic endocrine cell differentiation and that the presence of primary cilia on islet cells may play a key role in this process. Diabetes 56:950 -959, 2007

Background information. TSEs (transmissible spongiform encephalopathies) are neurodegenerative disorders affecting humans and animals. PrPSc, a conformationally altered isoform of the normal prion protein (PrPC), is thought to be the pathogenic agent. However, the biochemical composition of the prion agent is still matter of debate. The potential transmission risk of the prion agent through biological fluids has been shown, but the development of competitive diagnostic tests and treatment for TSEs requires a more comprehensive knowledge of the agent and the cellular mechanisms by which it is disseminated. With this aim, we initiated characterization of the prion agent and the pathways by which it can be propagated using the cellular model system neuroblastoma (N2a). Results. The present study shows that N2a cells infected with scrapie release the prion agent into the cell culture medium in association with exosome‐like structures and viral particles of endogenous origin. We found that both prion proteins and scrapie infectivity are mainly associated with exosome‐like structures that contain viral envelope glycoprotein and nucleic acids, such as RNAs. Conclusions. The dissemination of prions in N2a cell culture is mediated through the exosomal pathway.

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