Comparison of Germline Mosaics of Genes in the Polycomb Group of Drosophila Melanogaster

The genes of the Polycomb group (PcG) repress the genes of the bithorax and Antennapedia complexes, among others. To observe a null phenotype for a PcG gene, one must remove its maternal as well as zygotic contribution to the embryo. Five members of the PcG group are compared here: Enhancer of Polycomb [E(Pc)], Additional sex combs (Asx), Posterior sex combs (Psc), Suppressor of zeste 2 [Su(z)2] and Polycomblike (Pcl). The yeast recombinase (FLP) system was used to induce mitotic recombination in the maternal germline. Mutant embryos were analyzed by staining with antibodies against six target genes of the PcG. The loss of the maternal component leads to enhanced homeotic phenotypes and to unique patterns of misexpression. E(Pc) and Su(z)2 mutations had only subtle effects on the target genes, even when the maternal contributions were removed. Asx and Pcl mutants show derepression of the targets only in specific cell types. Psc shows unusual effects on two of the targets, Ultrabithorax and abdominal-A. These results show that the PcG genes do not act only in a common complex or pathway; they must have some independent functions.     

Expression of novel genes linked to the androgen-induced, proliferative shutoff in prostate cancer cells

Androgens control cell numbers in the prostate through three separate pathways: (a) inhibition of cell death, (b) induction of cell proliferation (Step-1) and (c) inhibition of cell proliferation (Step-2, proliferative shutoff). The mechanisms underlying these phenomena are incompletely understood. The human prostate carcinoma LNCaP variants express these pathways as follows: LNCaP-FGC express both steps, LNCaP-LNO expresses Step-2, LNCaP-TAC expresses Step-1, and LNCaP-TJA cells express neither step. These cells facilitated the search for mediators of the androgen-induced proliferative shutoff pathway. Androgen exposure for 24 h or longer induced an irreversible proliferative shutoff in LNCaP-FGC cells. The Wang and Brown approach for identifying differentially expressed mRNAs was used to search for mediators of Step-2. Ten unique inserts were identified and from those ten, three genes were further studied. The basal expression of these genes in shutoff-negative variants was not affected by androgen exposure. They were induced by androgens in shutoff-positive LNCaP variants and the androgen receptor-transfected, shutoff-positive, MCF7-AR1 cells. These genes were induced only in the range of androgen concentrations that elicited the shutoff response. Time course analysis showed that their induction precedes the commitment point by 12–18 h. In addition, they were expressed in the normal prostate during proliferative shutoff. These features suggest that the candidate genes have a role in the regulation cascade for proliferative shutoff.     

Localization of serotonin within tanycytes of the rat median eminence

Summary Formaldehyde and glyoxylic acid histochemical methods were employed to examine monoamine fluorescence of the rat median eminence. Tanycytes of the median eminence contained a yellow histofluorescence which was verified with microspectrofluorometry as due to the presence of serotonin. Catecholamine-containing varicosities, arranged in linear profiles throughout the depth of the median eminence, were observed. These linear profiles appeared to follow the contours of serotonin-containing tanycytes. Organculture experiments supported the hypothesis that the serotonin associated with tanycytes is localized within the tanycytes and does not arise from an extrahypothalamic source of nerve terminals. These data provide evidence that a tanycytic catecholamine-indoleamine morphological juxtaposition occurs in a manner reminiscent of that of another circumventricular organ, the pineal.Supported by USPHS Grants NS11642 and AM-19761USPHS Career Development Awardee NS-00259     

Microcommunities of algae on a Sphagnum mat

The algal epiphytes of three species of Sphagnum from the mat edge of an acid bog were quantitatively sampled over three months. On the basis of differences in total algal abundance, algal diversity, and the growth of certain algal species and species groups, two significantly different algal communities were recognized. While these communities were only centimeters apart, they differed in physical, biological and nutrient parameters, with lower, moister plots having more algae, higher algal diversity, and lower concentrations of phosphate, ammonium, and silicate ions.     

Stimulation ofEscherichia coli adenylate cyclase by lactose in strains carrying mutations in lactose permease

When a wild-type strain ofEscherichia coli contains lactose permease, the accumulation of cyclic AMP (cAMP) by intact cells isinhibited by lactose. This inhibitory effect of lactose is observed in a strain with a mutant cAMP phosphodiesterase and therefore involves a regulation of adenylate cyctase activity. Some E. coli strains carrying mutations in lactose permease show an effect opposite to that of the wild-type strain; the accumulation of cAMP by intact cells isstimulated by lactose, but only when the mutant permease is present. Insertion of lactose permease into the membrane of ceils can produce a change in the specific activity of adenylate cycIase; induction of the wild-type transporter is correlated with a decrease in the specific activity, while implantation of a mutant form of lactose permease can lead to an increase in the specific activity. From these data, it is suggested that the state of the lactose transporter in the cell membrane influences the activity of adenytate cyclase.     

Evidence that plasma membrane electrical potential is required for vesicular stomatitis virus infection of MDCK cells: A study using fluorescence measurements through polycarbonate supports

Summary We used fluorescence microscopy of Madin-Darby Canine Kidney (MDCK) cells grown on polycarbonate filters to study a possible link between plasma membrane electrical potential (_pm) and infectivity of vesicular stomatitis virus (VSV). Complete substitution of K⁺ for extracellular Na⁺blocks VSV infection of MDCK cells as well as baby hamster kidney (BHK) cells. When we independently perfused the apical and basal-lateral surfaces of high resistance monolayers, high K⁺ inhibited VSV infection of MDCK cells only when applied to the basal-lateral side; high K⁺ applied apically had no effect on VSV infection. This morphological specificity correlates with a large decrease in _pm of MDCK cells when high K⁺ buffer is perfused across the basal-lateral surface. Depolarization of the plasma membrane by 130 mm basal K⁺ causes a sustained increase of cytosol pH in MDCK cells from 7.3 to 7.5 as reported by the fluorescent dye BCECF. Depolarization also causes a transient increase of cytosol Ca²⁺ from 70 to 300 nm as reported by the dye Fura-2. Neither increase could explain the block of VSV infectivity by plasma membrane depolarization. One alternative hypothesis is that _pm facilitates membrane translocation of viral macromolecules as previously described for colicins, mitochondrial import proteins, and proteins secreted by Escherichia coli.We thank Kenneth Spring for many helpful discussions concerning fluorescence digitized imaging systems, James Russell for his collaboration in the design of our imaging system, Herbert Chase for suggestions on dye loading into MDCK cells, and Manfred Schubert and George Harmison for providing expertise on VSV.     

A regional study of developing rat brain: The accumulation and distribution of proteolipid proteins

The accumulation and distribution of proteolipid proteins in rat brain and selected brain regions (cerebellum, cerebral cortex, basal ganglia, and hippocampus) were studied during early postnatal development. In whole brain an eightfold increase of proteolipid was observed between ten and 33 days after birth. This was reflected in the separate regions examined where the proteolipid protein content increased six- to ten-fold during the same period. The basal ganglia and cerebral cortex contributed the greatest amount to the total proteolipid present. However, at 28–33 days the greatest concentration (mg/g tissue) was observed in the basal ganglia and hippocampus. When the proteolipid protein preparations were examined by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, distinctive, heterogeneous patterns for each brain region were obtained. Proteolipid from basal ganglia (the region richest in white matter) consisted primarily of two major protein bands with apparent molecular weights of approximately 21,500 and 26,000. Both of these bands dramatically increased in quantity during myelination, and the larger protein coelectrophoresed with isolated myelin proteolipid protein. Both bands were also found present in proteolipid preparations from the other brain regions but in varying amounts relative to the total. The data suggest that the increase in proteolipid observed during this developmental period was due in large measure to the accumulation of myelin-specific proteolipids, but also that a significant proportion of the increase was due to the accumulation of nonmyelin components.