Sex-related differences in the nuclear population of postpubertal rat pineal gland. A quantitative study.

Male and female parenchymal pineal cell types have been studied throughout postpubertal development to determine the existence of sex-related differences on a time basis. Six age groups (2, 3, 4, 8, 15 and 24 months) of eight rats (4 males and 4 females) were used in this study. Nuclei of both parenchymal pineal cell types were counted in 5 areas of 26.377 microns 2 per pineal gland on semithin sections. Nonparametric statistics of our results (Mann-Whitney U-test and Kruskal-Wallis H-test) demonstrated significant differences between male and female pinealocytes through the stages studied. In all age groups, the number of nuclei per unit area was larger in female rats. Pineoglial cells did not show significant sex-related differences.     

Cell proliferation in the developing rat pineal gland. A bromodeoxyuridine immunohistochemical study

The immunohistochemical detection of bromodeoxyuridine (BrdU) was used to study the cell proliferation in the developing rat pineal gland, from the appearance of pineal primordium in the embryonic day 15 (E15) until 30 days after birth. The results showed three different proliferative phases. From E15 to E21, the pineal gland shows a phase of rapid proliferation. The second phase corresponds to the first postnatal week, in which the number of labeled cells per surface unit decreases suddenly to values between 20% to 10% of those of embryonic period. From the second postnatal week onwards, the number of BrdU-positive cells progressively decreases.     

REV3 is required for spontaneous but not methylation damage-induced mutagenesis of Saccharomyces cerevisiae cells lacking O6-methylguanine DNA methyltransferase

O6-methylguanine (O6-MeG) DNA methyltransferase (MTase) removes the methyl group from a DNA lesion and directly restores DNA structure. It has been shown previously that bacterial and yeast cells lacking such MTase activity are not only sensitive to killing and mutagenesis by DNA methylating agents, but also exhibit an increased spontaneous mutation rate. In order to understand molecular mechanisms of endogenous DNA alkylation damage and its effects on mutagenesis, we determined the spontaneous mutational spectra of the SUP4-o gene in various Saccharomyces cerevisiae strains. To our surprise, the mgt1 mutant deficient in DNA repair MTase activity exhibited a significant increase in G:C-->C:G transversions instead of the expected G:C-->A:T transition. Its mutational distribution strongly resembles that of the rad52 mutant defective in DNA recombinational repair. The rad52 mutational spectrum has been shown to be dependent on a mutagenesis pathway mediated by REV3. We demonstrate here that the mgt1 mutational spectrum is also REV3-dependent and that the rev3 deletion offsets the increase of the spontaneous mutation rate seen in the mgt1 strains. These results indicate that the eukaryotic mutagenesis pathway is directly involved in cellular processing of endogenous DNA alkylation damage possibly by the translesion bypass of lesions at the cost of G:C-->C:G transversion mutations. However, the rev3 deletion does not affect methylation damage-induced killing and mutagenesis of the mgt1 mutant, suggesting that endogenous alkyl lesions may be different from O6-MeG.     

The economic value and sustainable harvest of plants and animals from the tropical forest: Assumptions,hypotheses, and methods

Recent studies of non-timber products from tropical rain forests have emphasized the economic value of these products and the sustainability of present harvests. Many of these studies rely upon a set of untested assumptions about the effects of harvesting upon the forest and the economic value of non-timber forest products in both the marketplace and in the daily life of rural people. These assumptions were formulated as a series of hypotheses during the workshop held in the Regional Community Forestry Training Center, Kesetsart University, Bangkok, in May 1992. The six hypotheses developed by workshop participants will be used to guide future research. As the hypotheses are tested, the data will be used to create a more realistic assessment of the sustainability and economic value of extraction of non-timber products from tropical forests.     

改变景观的力量——德克·西蒙斯教授专访

在今天,我们的生存环境面临着诸多挑战,包括气候变化,生物多样性减少,可用于发展的土地资源接近上限等等。面对这些问题,前荷兰首席国家风景园林师德克·西蒙斯认为我们必须关注那些能够改变景观的力量,不管它们是水利工程、旅游业、农业还是新能源。西蒙斯在文中介绍了他的过程导向方法论的思想起点,并通过几个获奖项目阐释了他如何运用这一方法。同时特别强调对生态系统的保护和修复是这个时代最重要的议题之一,也是我们这一代人最重要的使命之一。作为风景园林师,设计结合研究是我们的有力武器。我们不能仅关注眼前工作,还需要用长远的眼光批判地看待整个城市化进程。