Non-invasive transgenic mouse genotyping using stool analysis.

Commonly applied genotyping of transgenic mice involves using tail or ear biopsies which may cause discomfort to the animal. We tested the possibility of polymerase chain reaction (PCR)-based mouse genotyping using stool specimens from three transgenic mouse lines that overexpress 10-18 transgene copies of human keratin polypeptide 18, as compared to genotyping using tail biopsies. Stool specimens were obtained with ease and provided easy detection of the human transgene product. The method was also able to detect endogenous mouse actin and keratin genes which presumably are present at two copies each. Nested PCR was not necessary for genotyping using stool-derived genomic material but did increase the relative magnitude of the signal obtained. The non-invasive genotyping method described herein offers a reproducible, sensitive and effective modality that could replace invasive tissue sampling procedures currently used to test thousands of genetically altered mice.

Mutation of a major keratin phosphorylation site predisposes to hepatotoxic injury in transgenic mice.

Simple epithelia express keratins 8 (K8) and 18 (K18) as their major intermediate filament (IF) proteins. One important physiologic function of K8/18 is to protect hepatocytes from drug-induced liver injury. Although the mechanism of this protection is unknown, marked K8/18 hyperphosphorylation occurs in association with a variety of cell stresses and during mitosis. This increase in keratin phosphorylation involves multiple sites including human K18 serine-(ser)52, which is a major K18 phosphorylation site. We studied the significance of keratin hyperphosphorylation and focused on K18 ser52 by generating transgenic mice that overexpress a human genomic K18 ser52--> ala mutant (S52A) and compared them with mice that overexpress, at similar levels, wild-type (WT) human K18. Abrogation of K18 ser52 phosphorylation did not affect filament organization after partial hepatectomy nor the ability of mouse livers to regenerate. However, exposure of S52A-expressing mice to the hepatotoxins, griseofulvin or microcystin, which are associated with K18 ser52 and other keratin phosphorylation changes, resulted in more dramatic hepatotoxicity as compared with WT K18-expressing mice. Our results demonstrate that K18 ser52 phosphorylation plays a physiologic role in protecting hepatocytes from stress-induced liver injury. Since hepatotoxins are associated with increased keratin phosphorylation at multiple sites, it is likely that unique sites aside from K18 ser52, and phosphorylation sites on other IF proteins, also participate in protection from cell stress.

Susceptibility to hepatotoxicity in transgenic mice that express a dominant-negative human keratin 18 mutant.

Keratins 8 and 18 (K8/18) are intermediate filament phosphoglycoproteins that are expressed preferentially in simple-type epithelia. We recently described transgenic mice that express point-mutant human K18 (Ku, N.-O., S. Michie, R.G. Oshima, and M.B. Omary. 1995. J. Cell Biol. 131:1303-1314) and develop chronic hepatitis and hepatocyte fragility in association with hepatocyte keratin filament disruption. Here we show that mutant K18 expressing transgenic mice are highly susceptible to hepatotoxicity after acute administration of acetaminophen (400 mg/Kg) or chronic ingestion of griseofulvin (1.25% wt/wt of diet). The predisposition to hepatotoxicity results directly from the keratin mutation since nontransgenic or transgenic mice that express normal human K18 are more resistant. Hepatotoxicity was manifested by a significant difference in lethality, liver histopathology, and biochemical serum testing. Keratin glycosylation decreased in all griseofulvin-fed mice, whereas keratin phosphorylation increased dramatically preferentially in mice expressing normal K18. The phosphorylation increase in normal K18 after griseofulvin feeding appears to involve sites that are different to those that increase after partial hepatectomy. Our results indicate that hepatocyte intermediate filament disruption renders mice highly susceptible to hepatotoxicity, and raises the possibility that K18 mutations may predispose to drug hepatotoxicity. The dramatic phosphorylation increase in nonmutant keratins could provide survival advantage to hepatocytes.

Genetic mapping indicates that VP4 is the rotavirus cell attachment protein in vitro and in vivo.

To identify the rotavirus protein which mediates attachment to cells in culture, viral reassortants between the simian rotavirus strain RRV and the murine strains EHP and EW or between the simian strain SA-11 and the human strain DS-1 were isolated. These parental strains differ in the requirement for sialic acid to bind and infect cells in culture. Infectivity and binding assays with the parental and reassortant rotaviruses indicate that gene 4 encodes the rotavirus protein which mediates attachment to cells in culture for both sialic acid-dependent and -independent strains. Using ligated intestinal segments of newborn mice and reassortants obtained between the murine strain EW and RRV, we developed an in vivo infectivity assay. In this system, the infectivity of EW was not affected by prior treatment of the enterocytes with neuraminidase, while neuraminidase treatment reduced the infectivity of a reassortant carrying gene 4 from RRV on an EW background more than 80% relative to the controls. Thus, VP4 appears to function as the cell attachment protein in vivo as well as in vitro.

Immunogenicity, antigenicity, and protection efficacy of baculovirus expressed VP4 trypsin cleavage products, VP5(1)* and VP8* from rhesus rotavirus.

Rhesus rotavirus (RRV) VP4 trypsin cleavage product VP5(1)*, a truncated form of VP5*, was expressed in baculovirus and found by immunoprecipitation to be antigenically similar to VP5* on the virion. Immunization of mice with VP5(1)* elicited neutralizing antibody that was found to be cross-reactive with viruses representing P genotypes 1, 3, 4, 6, 7, and 8. Baculovirus expressed trypsin cleavage products, VP8* (amino acids 1-246) and VP5(1)* (amino acids 247-474), were tested for their ability to elicit a protective response in a murine model of passive protection. These results were compared to those obtained with baculovirus expressed RRV VP4. Dams immunized with baculovirus expressed RRV VP4 gave birth to pups protected from RRV virus challenge. Neither VP5(1)* nor VP8* was as effective at generating protective immunity as full length VP4. However, antibody to VP5(1)* was more effective than antibody to VP8* at mediating protection even though the neutralizing antibody titers as measured by hemagglutination inhibition and focus reduction neutralization were similar.

Active immunity against rotavirus infection in mice is correlated with viral replication and titers of serum rotavirus IgA following vaccination.

Using an adult mouse model to study active immunity against rotavirus infection, it was previously shown that oral immunization with some, but not all, animal rotavirus strains induced protection against subsequent infection following oral challenge with the murine rotavirus strain EDIM. To determine if a specific rotavirus protein could be associated with protection in this model, mice were immunized with a series of 18 reassortants between the fully protective EDIM strain and a partially protective heterologous rotavirus strain (RRV-G). Reassortants that contained genes for EDIM proteins responsible for protection were anticipated to provide complete protection; however, no EDIM proteins were found to be both necessary and sufficient for full protection. Instead, protection was found to be highly correlated with viral shedding (P = 0.005) and with serum rotavirus IgA titers stimulated by the different reassortants (P < 0.001). This indicated that protection was related to the intestinal replication properties of the different reassortants rather than to specific immunogenic properties of EDIM proteins. This conclusion was supported by the finding that the titers of serum rotavirus IgA, but not IgG, stimulated in mice following oral immunization with a series of animal rotaviruses was directly related to protection against EDIM. If these findings can be extended to humans, they suggest that the efficiency of intestinal replication following oral inoculation with a live rotavirus vaccine candidate may be the primary determinant of successful immunization.

Murine rotavirus genes encoding outer capsid proteins VP4 and VP7 are not major determinants of host range restriction and virulence.

Simian rotavirus (RRV) and murine rotavirus (EDIM-RW) differ dramatically in the oral inoculum required to cause diarrheal disease in neonatal mouse pups and in their ability to spread and cause disease in uninoculated littermates. A genetic approach was used to explore the molecular basis of these differences. Reassortant viruses were produced in vivo by coinfecting infant mice with RRV and EDIM-RW. Reassortant viruses were isolated by plaque purification of progeny virus obtained from mouse pup intestines on MA104 cells. The plaque-purified reassortants were evaluated for 50% diarrhea dose (DD50) and for the ability to spread and cause diarrhea in uninoculated littermates. The parental RRV strain had a DD50 of 10(5) PFU per animal, while the EDIM-RW parental strain had a DD50 of less than 1 PFU per animal. RRV never spreads from inoculated to uninoculated littermates and causes disease. Twenty-three reassortants were tested. Of great interest were the reassortants D1/5 and C3/2, which derived genes 4 and 7 (encoding VP4 and VP7) from RRV. These viruses had a DD50 similar or identical to that of EDIM-RW and spread efficiently from inoculated mouse pups to uninoculated pups. We conclude that the major outer capsid proteins VP4 and VP7 are not primarily responsible for virulence or host range restriction in the mouse model using a homologous murine rotavirus.

Efficacy of enrofloxacin in the treatment of respiratory pasteurellosis in rabbits.

Fourteen New Zealand White rabbits with respiratory signs of naturally occurring Pasteurella multocida infections were treated with either an injectable or water-soluble oral formulation of enrofloxacin. Antimicrobial efficacy was evaluated by scoring clinical signs in the rabbits and recovery of the organisms. Seven (87%) of eight rabbits treated with the injectable regimen (5 mg/kg every 12 hours for 14 days) became culture-negative with no clinical signs within 72 hours after initiation of treatment. Six rabbits treated with the oral formulation (200 mg/liter of drinking water for 14 days) also became culture-negative and had no clinical signs 3 to 7 days after treatment began, but P. multocida was recovered from several sites in three (50%) rabbits. No rabbits showed any signs of gastroenteric disturbances.

Pharmacokinetic properties of enrofloxacin in rabbits.

The pharmacokinetic properties of the fluoroquinolone antimicrobial enrofloxacin were studied in New Zealand White rabbits. Four rabbits were each given enrofloxacin as a single 5 mg/kg of body weight dosage by IV, SC, and oral routes over 4 weeks. Serum antimicrobial concentrations were determined for 24 hours after dosing. Compartmental modeling of the IV administration indicated that a 2-compartment open model best described the disposition of enrofloxacin in rabbits. Serum enrofloxacin concentrations after SC and oral dosing were best described by a 1- and 2-compartment model, respectively. Overall elimination half-lives for IV, SC, and oral routes of administration were 2.5, 1.71, and 2.41 hours, respectively. The half-life of absorption for oral dosing was 26 times the half-life of absorption after SC dosing (7.73 hours vs 0.3 hour). The observed time to maximal serum concentration was 0.9 hour after SC dosing and 2.3 hours after oral administration. The observed serum concentrations at these times were 2.07 and 0.452 micrograms/ml, respectively. Mean residence times were 1.55 hours for IV injections, 1.46 hours for SC dosing, and 8.46 hours for oral administration. Enrofloxacin was widely distributed in the rabbit as suggested by the volume of distribution value of 2.12 L/kg calculated from the IV study. The volume of distribution at steady-state was estimated at 0.93 L/kg. Compared with IV administration, bioavailability was 77% after SC dosing and 61% for gastrointestinal absorption. Estimates of predicted average steady-state serum concentrations were 0.359, 0.254, and 0.226 micrograms/ml for IV, SC, and oral administration, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)