Publications

We developed a transgenic mouse line that expresses the G(i)-coupled RASSL (receptor activated solely by synthetic ligand) Ro1 in astrocytes to study astrocyte-neuronal communication. Surprisingly, we found that all transgenics expressing Ro1 developed hydrocephalus. We analyzed these mice in an effort to develop a new model of hydrocephalus that will further our understanding of the pathophysiology of the disease. Expression of Ro1 was restricted to astrocytes by crossing the transgenic hGFAP-tTA (tet transactivator behind the human glial fibrillary acidic protein promoter) mouse line with the transgenic tetO-Ro1/tetO-LacZ mouse line. This cross produced double-transgenic mice that expressed Ro1 in astrocytes. All double transgenics developed hydrocephalus by postnatal day 15, whereas single-transgenic littermate controls appeared normal. Hydrocephalic Ro1 mice displayed enlarged ventricles, partial denudation of the ependymal cell layer, altered subcommissural organ morphology, and obliteration of the cerebral aqueduct. Severely hydrocephalic mice also had increased levels of phospho-Erk and GFAP expression. Administration of doxycycline to breeding pairs suppressed Ro1 expression and the onset of hydrocephalus in double-transgenic offspring. Ro1 animals maintained on dox did not develop hydrocephalus; however, if taken off doxycycline at weaning, double-transgenic mice developed enlarged ventricles within 7 weeks, indicating that Ro1 expression also induces hydrocephalus in adults. This study discovered a new model of hydrocephalus in which the rate of pathogenesis can be controlled enabling the study of the pathogenesis of both juvenile and adult onset hydrocephalus.

Viruses encounter changing selective pressures during transmission between hosts, including host-specific immune responses and potentially varying functional demands on specific proteins. The human immunodeficiency virus type 1 Nef protein performs several functions potentially important for successful infection, including immune escape via down-regulation of class I major histocompatibility complex (MHC-I) and direct enhancement of viral infectivity and replication. Nef is also a major target of the host cytotoxic T-lymphocyte (CTL) response. To examine the impact of changing selective pressures on Nef functions following sexual transmission, we analyzed genetic and functional changes in nef clones from six transmission events. Phylogenetic analyses indicated that the diversity of nef was similar in both sources and acutely infected recipients, the patterns of selection across transmission were variable, and regions of Nef associated with distinct functions evolved similarly in sources and recipients. These results weighed against the selection of specific Nef functions by transmission or during acute infection. Measurement of Nef function provided no evidence that the down-regulation of either CD4 or MHC-I was optimized by transmission or during acute infection, although rare nef clones from sources that were impaired in these activities were not detected in recipients. Nef-specific CTL activity was detected as early as 3 weeks after infection and appeared to be an evolutionary force driving the diversification of nef. Despite the change in selective pressure between the source and recipient immune systems and concomitant genetic diversity, the majority of Nef proteins maintained robust abilities to down-regulate MHC-I and CD4. These data suggest that both functions are important for the successful establishment of infection in a new host.