Life-history analysis of an Artemia population in a changing environment

The Anemia monica Verrill population in Mono Lake, Californiahas two generations per year. Despite similarities in the year-to-yearlife history patterns, some important differences developedbetween 1979 and 1981. The first generation hatches from overwinteringcysts in early spring and reaches maturity by the end of May.The first-generation females reproduce ovoviviparously, givingrise to a second generation which matures between mid-July andAugust. In July, both first and second generation females beginproducing overwintering cysts. The population reaches it maximumin late summer, then declines to low numbers by November. Theabundance of the first generation in June declined from a meanof 20 000 m^–2 to 2400 m^–2. Despite the smaller firstgeneration, the second generation in 1980 and 1981 was at leastas abundant as in 1979. These differences are indicative ofa change in the Artemia population dynamics in Mono Lake. ¹Address for correspondence: Hawaii Institute of Marine Biology,University of Hawaii, P.O. Box 1346 Kaneohe, HI 96744-1346,USA.     

The Chlamydomonas cell cycle is regulated by a light/dark-responsive cell-cycle switch

Cultures of the unicellular green alga Chlamydomonas reinhardii can be synchronized by light/dark cycling not only under photoautotrophic but also under mixotrophic growth conditions. We observed that cultures synchronized in the presence of acetate continue to divide synchronously for one cell-cycle period when transferred to heterotrophic growth conditions. This finding enabled us to investigate the differential effects of light on cell growth and cell division. When cells were exposed to continuous light at the beginning of the growth period they entered the division phase earlier than dark-grown cells as a consequence of an increased growth rate. Illumination at the end of the growth period, however, caused a considerable delay in cell division and an extended growth period. The light-induced delay in cell division was also observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. This finding demonstrates that cell division is directly influenced by a light/dard-responsive cell-cycle switch rather than by light/dark-dependent changes in energy metabolism. The importance of this light/dark control to the regulation of the Chlamydomonas cell cycle was investigated in comparison with other control mechanisms (size control, time control). We found that the light/dard-responsive cell-cycle switch regulates the transition from G1-to S-phase. This control mechanism is effective in cells which have attained the commitment to at least one round of DNA replication and division but have not attained the maximal cell mass which initiates cell division in the light.Abbreviations dCTP deoxycytidine 5-triphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

The regulatory protein GAL80 is a determinant of the chromatin structure of the yeast GAL1-10 control region

Chromatin in the regions between the upstream activator sequence and the 5' ends of the yeast GAL1 and GAL10 genes has been analyzed by DNase I chromosomal footprinting and micrococcal nuclease digestion using the indirect end-labeling approach. Comparison of wild type chromatin digests to naked DNA digests shows that there are specific regions of these upstream sequences which are strongly protected in chromatin. Comparison to chromatin digests from cells disrupted for the positive regulatory gene, GAL4, or the negative regulatory gene, GAL80, and thus lacking GAL4 or GAL80 function, shows that these regions of protection in wild type chromatin are GAL80-dependent but not GAL4-dependent. The protected regions include DNA lying on (GAL10) or near (GAL1) the respective TATA boxes. These protections are present in both noninduced and induced cells. Both DNA strands are equally protected. Upstream of GAL1 there is a second protected region. This protection shows considerable expression and strand dependence. These observations provide the first evidence that the GAL80 function influences chromatin structure and suggest possible mechanisms by which GAL80 modulates the GAL1 and 10 promoters in induced cells. Micrococcal nuclease digests also suggest a role for GAL80 in a distinctive higher order organization of the intergenic region, perhaps involving multiprotein complexes.     

Effects of light and acetate on the liberation of zoospores by a mutant strain ofChlamydomonas reinhardtii

In light-dark-synchronized cultures of the unicellular green algaChlamydomonas reinhardtii, release of zoospores from the wall of the mother cell normally takes place during the second half of the dark period. The recently isolated mutant ls, however, needs light for the liberation of zoospores when grown photoautotrophically under a 12 h light-12 h dark regime. The light-induced release of zoospores was found to be prevented by addition of the photosystem-II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Furthermore, light dependence of this process was shown to be abolished when the mutant ls was grown either photoautotrophically under a 14 h light-10 h dark regime or in the presence of acetate. Our findings indicate that the light-dependency of zoospore liberation observed in cultures of this particular mutant during photoautotrophic growth under a 12 h light-12 h dark regime might be attributed to an altered energy metabolism. The light-induced release of zoospores was found to be prevented by addition of cycloheximide or chloramphenicol, antibiotics which inhibit protein biosynthesis by cytoplasmic and organellar ribosomes, respectively. Actinomycin D, an inhibitor of RNA synthesis, however, did not affect the light-induced liberation of zoospores.Sporangia accumulate in stationary cultures of the mutant ls. Release of zoospores was observed when these sporangia were collected by centrifugation and incubated in the light after resuspension in fresh culture medium. Since liberation of zoospores was not observed after dilution of the stationary cultures with fresh culture medium, we suppose that components which interfere with the action of the sporangial autolysin are accumulated in the culture medium of the mutant ls.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Effect of acute and chronic hypernatremia on myoinositol and sorbitol concentration in rat brain and kidney

In animal models of hypernatremia, increases in brain electrolyte content account for the entire increase in osmolality in acute but not chronic hypernatremia, suggesting that there is generation of additional intracellular solutes ("idiogenic osmoles") in chronic hypernatremic states. In the present study, the concentration of the polyols myoinositol and sorbitol and water content were determined in the brain and kidneys of rats made acutely (2 hours) and chronically (72 hours) hypernatremic by intraperitoneal injection of NaCl and water restriction. Both the brain and the kidney responded to chronic hypernatremia with increased levels of myoinositol. Sorbitol levels increased in the kidney in response to both acute and chronic hypernatremia. Water content dropped in acute hypernatremia, but remained unchanged during chronic hyperosmolar challenge. We conclude that the polyols, myoinositol and sorbitol, may play a significant role in cellular osmoregulation in brain and kidney during chronic hypernatremia in the rat.     

Modified structure and kinetics of cytochrome-c oxidase in fibroblasts from patients with Leigh syndrome

In this study we compared the properties of cytochrome-c oxidase (COX) in cultured fibroblasts from two patients with Leigh Syndrome with COX from control fibroblasts. The fibroblasts from patients showed decreased growth reates and elevated lactate production. COX activity of patients fibroblasts was about 25% of control. Kinetic studies with isolated mitochondria showed a higher K_m for cytochrome c and a markedly reduced molecular turnover of COX from patients, indicating a different structure of the enzyme. A biphasic change of COX activity was obtained by titration of dodecylmaltoside solubilized mitochondria from control fibroblasts with increasing concentrations of anions. With patient mitochondria we found only the inhibiting phase of COX activity and, in contrast to control mitochondria, irreversible inhibition of COX activity by guanidinium chloride. ELISA titrations with monoclonal antibodies to subunit II, IV, Vab, VIac and VIIab indicated a normal amount of mitochondrial coded subunit II, but a reduced amound of nuclear coded subunits. The data indicate incompletely assembled nuclear coded subunits of COX from patient fibroblasts.     

Androgen receptor heterogeneity in LNCaP cells is caused by a hormone independent phosphorylation step

Androgen receptor synthesis and modification were studied in the human LNCaP cell line. Immunoblotting showed that the androgen receptor migrated as a closely spaced 110–112 kDa doublet on SDS-PAGE gels. Most of the receptor protein is present in the higher molecular mass form. Labelling experiments with [³⁵S]methionine showed that the androgen receptor is synthesized as a single 110 kDa protein which is rapidly converted to a 112 kDa protein. Upon alkaline phosphatase treatment a gradual elimination of the 112 kDa isoform with a concomitant increase of the 110 kDa isoform was seen, indicating that the observed 110 to 112 kDa upshift reflects androgen receptor phosphorylation. Furthermore, it is shown that both isoforms can bind hormone and undergo a hormone dependent transformation to a tight nuclear binding form, indicating that the 110 to 112 kDa conversion is not an obligatory step for hormone binding or receptor transformation.