Homozygous staggerer (sg) mice show a characteristic severe cerebellar ataxia due to a cell-autonomous defect in the development of Purkinje cells. These cells show immature morphology, synaptic arrangement, biochemical properties and gene expression, and are reduced in numbers. In addition, sg heterozygotes show accelerated dendritic atrophy and cell loss, suggesting that sg has a role in mature Purkinje cells. Effects of this mutation on cerebellar development have been studied for 25 years, but its molecular basis has remained unknown. We have genetically mapped staggerer to an interval of 160 kilobases on mouse chromosome 9 which was found to contain the gene encoding RORalpha, a member of the nuclear hormone-receptor superfamily. Staggerer mice were found to carry a deletion within the RORalpha gene that prevents translation of the ligand-binding homology domain. We propose a model based on these results, in which RORalpha interacts with the thyroid hormone signalling pathway to induce Purkinje-cell maturation.

Chemokines are involved in recruitment and activation of hematopoietic cells at sites of infection and inflammation. The M3 gene of ␥HV68, a gamma-2 herpesvirus that infects and establishes a lifelong latent infection and chronic vasculitis in mice, encodes an abundant secreted protein during productive infection. The M3 gene is located in a region of the genome that is transcribed during latency. We report here that the M3 protein is a high-affinity broad-spectrum chemokine scavenger. The M3 protein bound the CC chemokines human regulated upon activation of normal T-cell expressed and secreted (RANTES), murine macrophage inflammatory protein 1␣ (MIP-1␣), and murine monocyte chemoattractant protein 1 (MCP-1), as well as the human CXC chemokine interleukin-8, the murine C chemokine lymphotactin, and the murine CX 3 C chemokine fractalkine with high affinity (K d ‫؍‬ 1.6 to 18.7 nM). M3 protein chemokine binding was selective, since the protein did not bind seven other CXC chemokines (K d > 1 M). Furthermore, the M3 protein abolished calcium signaling in response to murine MIP-1␣ and murine MCP-1 and not to murine KC or human stromal cell-derived factor 1 (SDF-1), consistent with the binding data. The M3 protein was also capable of blocking the function of human CC and CXC chemokines, indicating the potential for therapeutic applications. Since the M3 protein lacks homology to known chemokines, chemokine receptors, or chemokine binding proteins, these studies suggest a novel herpesvirus mechanism of immune evasion.Chemokines are chemoattractant and immunomodulatory molecules that play a central role in many inflammatory processes (30). They are divided into four structural groups based on the number and arrangement of conserved cysteines and are consequently named CC, CXC, C, and CX 3 C chemokines. CC chemokines generally regulate macrophages and lymphocytes; they include monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein 1␣ (MIP-1␣), and regulated upon activation of normal T-cell expressed and secreted (RANTES). CXC chemokines include interleukin-8 (IL-8), monokine induced by gamma interferon (Mig), macrophage inflammatory protein 2 (MIP-2), stromal cell-derived factor 1 (SDF-1), granulocyte chemotactic protein 2 (GCP-2), interferon-inducible protein 10 (IP-10), B-cell-attracting chemokine (BCA-1), and KC. While many CXC chemokines stimulate the activity of neutrophils, some regulate lymphocytes. The only members of the C and CX 3 C chemokine families are lymphotactin and fractalkine, respectively.Given the importance of chemokines in the immune system, it is not surprising that viruses have evolved mechanisms for interacting with the chemokine system. Both poxviruses and herpesviruses use two known strategies for interacting with the chemokine system, one via virus-encoded chemokine receptor homologs and one via virus-encoded chemokine homologs (see, e.g., references 24 and 28; reviewed in references 16 and 19). An additional strategy, secretion of chemokine binding proteins with novel s...

The M3 protein encoded by murine gamma herpesvirus68 (gamma HV68) functions as an immune system saboteur by the engagement of chemoattractant cytokines, thereby altering host antiviral inflammatory responses. Here we report the crystal structures of M3 both alone and in complex with the CC chemokine MCP-1. M3 is a two-domain beta sandwich protein with a unique sequence and topology, forming a tightly packed anti-parallel dimer. The stoichiometry of the MCP-1:M3 complex is 2:2, with two monomeric chemokines embedded at distal ends of the preassociated M3 dimer. Conformational flexibility and electrostatic complementation are both used by M3 to achieve high-affinity and broad-spectrum chemokine engagement. M3 also employs structural mimicry to promiscuously sequester chemokines, engaging conservative structural elements associated with both chemokine homodimerization and binding to G protein-coupled receptors.

Gammaherpesviruses such as Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus are important human pathogens that establish long-term latent infections. Understanding of the initiation and maintenance of latent infections has important implications for the prevention and treatment of gammaherpesvirusrelated diseases. Although much is known about gammaherpesvirus pathogenesis, it is unclear how the infectious dose of a virus influences its ability to establish latent infection. To examine the relationship between the infectious dose and gammaherpesvirus latency, we inoculated wild-type mice with 0.01 to 10 6 PFU of murine gammaherpesvirus 68 (␥HV68) and quantitatively measured latency and acute-phase replication. Surprisingly, during latency, the frequencies of ex vivo reactivation were similar over a 10 7 -fold range of doses for i.p. infection and over a 10 4 -fold range of doses for intranasal infection. Further, the frequencies of cells harboring viral genome during latency did not differ substantially over similar dose ranges. Although the kinetics of acute-phase replication were delayed at small doses of virus, the peak titer did not differ significantly between mice infected with a large dose of virus and those infected with a small dose of virus. The results presented here indicate that any initiation of infection leads to substantial acute-phase replication and subsequent establishment of a maximal level of latency. Thus, infections with doses as small as 0.1 PFU of ␥HV68 result in stable levels of acute-phase replication and latent infection. These results demonstrate that the equilibrium level of establishment of gammaherpesvirus latency is independent of the infectious dose and route of infection.Gammaherpesviruses such as Epstein-Barr virus (EBV) are ubiquitous and efficiently establish long-term latent infections. Although the frequency of cells positive for EBV genome during latency differs significantly among individuals (11), it is stable over time. It is unknown whether this reflects differences in infecting doses, variations between viruses, or variations between hosts regardless of the dose. In addition, it is unclear how acute-phase replication of gammaherpesviruses relates to the level of latency. For example, data demonstrating that vaccinations reduce acute-phase replication but do not alter long-term latency (13,19) suggest that efficient acute infection is not a mandatory step for establishment of latency by a gammaherpesvirus. For alphaherpesviruses such as herpes simplex virus type 1 (HSV-1), establishment of latency correlates with the ability to initiate acute-phase replication (9). A detailed analysis demonstrated that the virus efficiently establishes a stable level of latency once acute-phase replication occurs above a threshold level (9,17,18). In contrast, for the betaherpesvirus cytomegalovirus (CMV), the extent of acutephase replication determines the load of latent viral genome (14,15). To determine how the infectious dose of a gammaherpesvirus relates to the effic...

The mouse vibrator mutation causes an early-onset progressive action tremor, degeneration of brain stem and spinal cord neurons, and juvenile death. We cloned the vibrator mutation using an in vivo positional complementation approach and complete resequencing of the resulting 76 kb critical region from vibrator and its parental chromosome. The mutation is an intracisternal A particle retroposon insertion in intron 4 of the phosphatidylinositol transfer protein alpha gene, causing a 5-fold reduction in RNA and protein levels. Expression of neurofilament light chain is also reduced in vibrator, suggesting one signaling pathway that may underlie vibrator pathology. The vibrator phenotype is suppressed in one intercross. We performed a complete genome scan and mapped a major suppressor locus (Mvb-1) to proximal chromosome 19.