The intricate processes involved in analysing a single Voyager image of the rings of Uranus are investigated. The unique image of the rings in forward scattered light shows the presence of numerous new rings not seen in either occultations or images in back scattered light.

Project LONGSTOP, the LONg-term Gravitational STudy of the Outer Planets, began as an attempt to investigate the problem of the stability of the outer planets — from Jupiter to Pluto — by means of modern numerical and analytical methods over 108 years, a timespan approaching the known age of the system. Modifications to the pure Newtonian 6-body system model were introduced and special care was devoted in choosing the initial conditions for the computed system to resemble the real one as much as possible. The expertise gained with the outer planets was later applied to another 6-body problem of our Solar System, the satellites of Uranus. The paper describes the various considerations leading to the model adopted, the method of integration, the error accumulation, the results achieved; a description is also given of the post-processing methods used. Among the main results are the discovery of so far unknown long periodic variations in the major semiaxes of the outer planets with periods of about 1 million years. The secular frequency of these energy variations involves the pericentres of Jupiter and Uranus and turns out to play a major role in shaping the dynamical structure of the Solar System. It appears also in a secular small divisor of much longer period (about 31 million years) which seems to be responsible for the accumulation of spectral lines in some regions of the long-periodic spectrum of the outer Solar System; it suggests that 100 million years might be long enough a timespan already to reveal the presence of non-regular — although small — regions of motion in the phase space.

A simple revised secular perturbation theory which incorporates the averaged secular effect of first-order near-resonances is derived. By including the effects of these near-resonances, the largest error in the secular frequencies is reduced from 16 percent to less than 3 percent. It is concluded that the revised secular perturbation theory is adequate for the quantitative modeling of the long-term perturbations in the Uranian satellite system. If incorporated within the general theory of Laskar (1986), this theory would lead to completely analytic theory.

An examination of Le Verrier's seventh-order expansion of the disturbing function has revealed only one non-trivial error in Le Verrier's work. The error occurs in a sixth order term in the eccentricities.

The effect of uv irradiation on the recovery of DNA synthesis is examined in a population of hare fibroblasts exhibiting heterozygosity with reference to the X-linked enzyme, glucose-6-phosphate-dehydrogenase (G-6-PD). These cells have been grown from skin explants of a hybrid female cross between Lepus timidus (female) and L. europaeus (male), the former carrying the G-6-PD gene for the slow-moving “T” variant and the latter with the fast-moving “E” variant gene. The hybrid, therefore, exhibits genetic mosaicism due to random inactivation in each cell, of one of the two X chromosomes in the embryonic stage. Exponentially growing cells from 13 fibroblast strains, comprising a wide range of E to T ratios, were exposed to moderately low dose of uv irradiation (6 J/m2). The recovery in DNA synthesis during the 2- to 8-h postirradiation period was calculated as the mean percentage rates of [3H]thymidine incorporated during the time as compared to the unirradiated zero-time controls. The results show a statistically significant positive correlation as determined by linear regression analysis between the levels of E and the rate of recovery in DNA synthesis. This is valid also at the higher dose of uv (21 J/m2). These results strengthen our earlier observations with 25-hydroxycholesterol that in the in vitro system the cell expressing the E variant is perhaps more resistant to cytotoxic agents. This also indicates that various factors contribute to the development of monotypism which include cell growth, cell death, mutation, and selection, to name a few.

In 1973, Dr. Earl Benditt and his associate reported extremely interesting and provocative findings in regard to the origin of atherosclerotic lesions (1). These investigators have been studying atherosclerotic lesions in autopsy specimens from black women who were heterozygous for glucose-6-phosphate dehydrogenase (G-6-PD), using techniques that had been developed for investigating the origin of neoplasms. They found many advanced atherosclerotic lesions are monotypic or at least have monotypic foci. With these findings they concluded that each atherosclerotic lesion probably arose from a single, genetically transformed cell and thus constituted a single clone (monoclonal origin). This had been shown to be the case for leiomyomas and for certain other neoplasms. The obvious inference to be drawn was that atherosclerotic lesions were in fact neoplasms. Since then many observations have been made on this phenomenon in a number of laboratories including ours. We have studied similar atherosclerotic lesions with monotypic foci and have concluded, from similar data to those reported by Dr. Benditt and his associate that the observed monotypism has causes other than monoclonism and hence it does not indicate monoclonal origin of the lesions (2).

In this study fibroblast cultures from the skin of 11 hybrid female hares that were heterozygous for glucose-6-phosphate dehydrogenase (G-6-PD) were grown in a standard culture medium containing successively increasing concentrations of 25-hydroxycholesterol. The hare cross was between Lepus timidus (T) females and Lepus europaeus (E) males. In cultures from 8 of the 11 hares there was a significant shift of T:E ratios toward E with increasing concentrations of 25-hydroxycholesterol. In 3 hares, some cultures with the higher concentrations of additive became phenotypically 100% E. The change of T:E ratios towards E appeared to occur because the 25-hydroxycholesterol was more toxic for the T-type cell. The results in this study contrast with those in a previous study of skin fibroblasts which include these same 11 hares. In the earlier study the fibroblasts were carried through multiple passages in the same standard medium used herein (but with no 25-hydroxycholesterol added). Seven of the eleven eventually exhibited only T-type cells. In 2 there was significant movement toward E but neither showed only E in any passage. The responses of the cells are presumably on a genetic basis. It is interesting but not expected that gene expressions enhancing survival and growth in one cellular environment can do the opposite in another.

The activities of DNA-dependent RNA polymerase and protein kinase in swine aortic nuclei were investigated after short-term feeding of cholesterol to the animals. Corresponding controls were maintained on a mash diet. Both enzyme activities increase in response to cholesterol feeding probably reflecting the need for synthesis of new proteins necessary for the increased cell growth observed in early atherogenesis. It could also be due to altered differentiation caused by low level damage to the genome. The protein kinase reported here appears to be the enzyme that associates with RNA polymerase II and is activated by cGMP. However, cAMP has an inhibitory effect. The phosphorylation of both histone and nonhistone classes is increased and corresponds to the length of cholesterol feeding.

Skin fibroblast cultures from hybrid hares (Lepus europaeus × Lepus timidus) exhibiting glucose-6-phosphate dehydrogenase (G-6-PD) mosaicism were followed for varying numbers of transfers. The majority of cultures either changed systematically in the ratio of G-6-PD variants, or exhibited, at some transfer, one type only. Changes occurred in both directions: toward higher T:E ratios or toward lower T:E ratios. Some cultures shifted from the apparent monotypic state to the ditypic state (usually from monotype T), suggesting that the apparent monotypes sometimes contain type E cells which fail to be detected, either due to limitations of assay sensitivity or to cytoplasmic factors of varying activity or concentration. The results are somewhat similar to those found in skin fibroblast cultures of heterozygous black female G-6-PD mosaics, and suggest the presence of factors, in one or the other of the X chromosomes, conferring a selective advantage on the cells of the corresponding type.