Regulation of NIH-3T3 cell G1 phase transit by serum during exponential growth.

The proliferation rate of mammalian cells is regulated normally in the G1 phase of the cell cycle. During this phase, it is convenient to assign positive and negative roles to the molecular programs that regulate the duration of G1 and the phase transition from G1 to S phase. Density-dependent inhibition of cellular proliferation results in an increase in the duration of G1. This form of regulation is due to both secreted factors and cell-cell contact. Serum is mitogenic to a variety of mammalian cell types. Because quiescent cells enter S phase as a result of serum addition to culture media, serum is usually regarded as a source of positive regulatory growth factors. We have measured the length of the G1, S and G2+M phases of NIH 3T3 cells during exponential growth as a function of cell density and serum concentration. The G1 length increases during exponential growth as a function of density while S and G2+M are relatively constant. Further, this increase in G1 phase time, or density mediated negative regulation, is inhibited by increasing serum concentration. This phenotype is saturable between 10% to 20% serum. Serum concentrations above 2.5% are able to increase the rate of cell cycling (decrease the G1 phase time) by inhibiting density dependent negative regulation of NIH 3T3.

Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to humans in rural housing.

An experimental assessment of methods to reduce rodent infestations in rural housing was conducted in Yosemite National Park, California, Sequoia/Kings Canyon National Parks, California, and Shenandoah National Park, Virginia. During pretreatment surveys, nearly all (63 of 68) selected units had past or ongoing rodent activity inside. Active infestations were found in 58.8% of the units. Peromyscus spp. represented 91.2% of all animals caught inside housing units. Despite little harborage, rodent activity was common near housing (290 animals/2,254 trap nights). The most common species present was Peromyscus maniculatus (43-50% of all captures). This species was especially frequent (49-87% of Peromyscus captures) around the foundations of housing units. Habitat had little effect on captures. There were 1.8 Peromyscus caught per unit along the foundations of housing in modified rural settings with grass lawns compared with 1.2 Peromyscus caught per unit in sites located in mature woodlands. During autumn of 1994, randomly selected housing units were rodent proofed by sealing openings associated with chases, roof eaves, and attics with insulation and wire mesh. Housing was examined and the fauna was resampled in the spring-summer of 1995. Rodent-proofed houses were infested significantly less often (3 of 28) than control houses (13 of 36) (P = 0.02) and the intensity of infestation was lower in experimental houses (6 versus 23 mice/treatment). More than 25% of the mice trapped inside the houses had been marked outside the houses during the three-day surveys, demonstrating movement of mice adjacent to the buildings into not rodent-proofed housing. As in the previous autumn, most of the animals captured in (98.9%) and along the foundations of the houses (77.5%) were Peromyscus spp. These results demonstrate that Peromyscus frequently invade rural housing but rodent-proofing effectively eliminates or substantially reduces rodent activity.

Mutagenicity of 2-amino-N6-hydroxyadenine at the tk locus in L5178Y strains differing in repair capabilities and karyotype.

The cytotoxicity and mutagenicity of 2-amino-N6-hydroxyadenine (AHA) were measured in strains of L5178Y differing in repair capabilities and karyotype. Strain LY-R83 is monosomic for chromosome 11 and is therefore hemizygous for the tk gene, while strains LY-R16 and LY-S1 are TK+/- heterozygotes. Both strain LY-R83 and LY-R16 are sensitive to UV light and are presumed to be deficient in the excision of pyrimidine dimers as shown for the parental strain, LY-R (Hagen et al., 1988; Szumiel et al., 1988). Strain LY-S1 is sensitive to the cytotoxic effects of ionizing radiation and is presumed to be defective in the repair of radiation-induced DNA double-strand breaks, as shown for the parental strain, LY-S (Evans et al., 1987a; Wlodek and Hittelman, 1987). The sensitivities of the three strains to the cytotoxic effects of AHA were similar. After a 4-hour treatment with AHA at 37 degrees C, the D37 for all three strains was approximately 35 ng/ml. The AHA-induced mutant frequency was similar for the hemizygous TK+ strain LY-R83 and the heterozygous TK +/- strain LY-R16, but was slightly higher for strain LY-S1 than for either LY-R strain at an AHA concentration of 100 ng/ml. The proportion of AHA-induced LY-S1 TK -/- mutants forming colonies with diameters less than 0.3 mm was much lower than following treatment with X radiation (24% vs. 61% for AHA and X radiation, respectively). These results indicate that the vast majority of AHA-induced TK -/- mutants harbor single gene mutations. AHA did not result in cyanide-insensitive oxygen uptake, and treatment with this compound did not induce a significant number of DNA single-strand breaks, DNA alkali labile lesions, or DNA degradation in either strain. However, two hours after AHA removal, DNA single-strand breaks and/or alkali-labile lesions, possibly due to the occurrence of DNA repair, were apparent in the DNA of both strain LY-R16 and strain LY-S1.