In vitro studies of poly(methyl methacrylate) adjuvants

Poly(methyl methacrylate) adjuvants, prepared by polymerizing monomeric methyl methacrylate in the presence of influenza virions or by addition of the virions to previously polymerized poly(methyl methacrylate) particles, were studied by means of the hemagglutination test, antibody binding, and electron microscopy. The results indicated that the virions were coated partly when the polymerization was carried out in the presence of the virus, whereas the virions were probably adsorbed when added to polymerized particles.     

The emergence of new DNA repeats and the divergence of primates

We have identified four genetic novelties that are fixed in specific primate lineages and hence can serve as phylogenetic time markers. One Alu DNA repeat is present in the human lineage but is absent from the great apes. Another Alu DNA repeat is present in the gorilla lineage but is absent from the human, chimpanzee, and orangutan. A progenitor Xba1 element is present in the human, chimpanzee, gorilla, and orangutan, but only in the human lineage did it give rise to a transposed progeny, Xba2. The saltatory appearance of Xba2 is an example of a one-time event in the evolutionary history of a species. The enolase pseudogene, known to be present as a single copy in the human, was found to be present in four other primates, including the baboon, an Old World monkey. Using the accepted value of 5 x 10(-9) nucleotide substitutions per site per year as the evolutionary rate for pseudogenes, we calculated that the enolase pseudogene arose approximately 14 million years ago. The calculated age for this pseudogene and its presence in the baboon are incongruent with each other, since Old World monkeys are considered to have diverged from the hominid lineage some 30 million years ago. Thus the rate of evolution in the enolase pseudogene is only about 2.5 x 10(-9) substitutions per site per year, or half the rate in other pseudogenes. It is concluded that rates of substitution vary between species, even for similar DNA elements such as pseudogenes. We submit that new DNA repeats arise in the genomes of species in irreversible and punctuated events and hence can be used as molecular time markers to decipher phylogenies.     

Postimplantation mouse development: whole embryo culture and micro-manipulation

Methods for growing whole mouse embryos in vitro have been greatly improved in the last two decades. The present technology enables embryos to develop remarkably close to what can be achieved in vivo from the pre-gastrula to the early organogenesis stages. The ability to grow whole embryos for a substantial period outside the uterine environment offers a unique opportunity to observe the progression of development, and permits the performance of direct manipulation on the embryo. Experiments combining whole embryo culture and micro-manipulation have led to the discovery of new information on lineage differentiation, tissue interaction and morphogenetic mechanisms that are associated with the establishment of the fetal body plan.     

Comet assay demonstrates a higher ultraviolet B sensitivity to DNA damage in dysplastic nevus cells than in common melanocytic nevus cells and foreskin melanocytes

We used the single cell gel electrophoresis assay (comet assay) to study ultraviolet B (UVB)-induced DNA damage in pigment cells. This assay detects DNA damage, mainly DNA strand breaks and alkali labile sites in the DNA molecule. We studied the effect of biologically relevant doses (comparable to 2-3 MED (minimal erythemal dose) for in vivo irradiated full-thickness skin) of monochromatic UVB light of 302 nm on cultured melanocytes derived from foreskin, common melanocytic nevi, and dysplastic nevi. We were able to demonstrate a linear dose-response relationship between UV dose and the migration coefficient of the comet tail in all three types of pigment cells. Nevus cells originating from dysplastic nevi showed the highest sensitivity to UVB irradiation: 65% higher induction of DNA damage compared to the induction in foreskin melanocytes. Common melanocytic nevus cells were most resistant and showed a 30% lower induction of DNA damage in comparison to foreskin melanocytes. Differences in chromatin structure and cell cycle profile may influence the results of the comet assay. Control experiments with x-ray irradiation, which is well known to produce direct DNA strand breaks via radical formation, revealed only small differences between the three types of melanocytic cells. It is unlikely, therefore, that intrinsic nuclear characteristics may account for the observed differences.     

Healthy aging: guidelines for cancer screening and immunizations

With increasing life expectancy over the past 50 years, screening for treatable illness and active measures to prevent disease and promote a healthy lifestyle have become increasingly important for older patients. In general, the benefits of such efforts have become more apparent, but depend also upon general health and life expectancy of the individual. Tests for malignancies of the breast, cervix, prostate, colon, skin, and oral cavity are considered to meet screening criteria. Immunization guidelines have been recently updated, and good evidence supports the benefit of protecting older patients from influenza and pneumococcal pneumonia. Counseling on prevention of falls and injuries in the home and on the highways can help reduce the risk of accidents.