Prolactin modifies the prostaglandin synthesis, prolactin binding and fluidity of mouse liver membranes

The objective of these studies was to determine if prolactin, known to induce its own receptors, alters the prostaglandin (PG) synthesis which could, in turn, modify the fluidity of the membrane and thus alter the functionality of prolactin receptors. Adult male C₃H mice were injected subcutaneously with 100 μg of oPRL every 4 h for 0, 24 or 48 h and sacrificed 8 h after receiving the last injection. Liver 100,000 × $\text{g}$ membrane pellets were used in the measurement of these parameters. The amount of binding of prolactin to these membranes increased with the duration of injections, the values being 179 and 244% of control values after 24 and 48 h of injections, respectively. The amounts of PGF_2α and PGE synthesized also increased after these injections, the values being 127 and 270% of control for PGF_2α and 634 and 695% of control values for PGE after 24 and 48 h of injections, respectively. Fluorescence polarization, an index of microviscosity, was decreased by 14 and 20% after 24 and 48 h of PRL administration, respectively. Previous studies have demonstrated simultaneous in vitro effects of prostaglandin on both prolactin receptors and membrane fluidity. The current data are in agreement with those observations and suggest that prolactin may modulate its own receptor by increasing the fluidity of the membrane in which it exists by alterations within the PG cascade. Such biochemical changes may then modify existing restraints and allow the hormone receptor to assume a more functional configuration.     

Putting the heat on sex determination

Sex determination and differentiation are inherently fascinating to both layperson and geneticist. Major advances have accelerated interest in the molecular genetic events mediating these processes in nematodes, flies, mice and humans. Far less attention has been paid to those organisms, particularly reptiles, where sex is determined by environmental cues. However, recent experimental evidence suggests that the two modes of sex determination may not only share common genetic elements, but may also be regulated by similar mechanisms. We argue that the ability to manipulate sex by temperature provides a particularly suitable model for exploring the molecular basis of this fundamental biological process.     

Territorialit?t und Brutbiologie der FeldlercheAlauda arvensis in einer intensiv genutzten Agrarlandschaft

Zusammenfassung In einer intensiv landwirtschaftlich genutzten Fläche des schweizerischen Mittellandes wurden 1983–1987 vier Feldlerchenaggregationen mit maximal 39 Brutpaaren untersucht. Die Tradition (Ortstreue) bestimmte in erster Linie die Revierwahl und das Verteilungsmuster. Die Reviere waren mit ha sehr groß; ihre Größe korrelierte negativ mit der Anzahl Parzellen pro Fläche und der Kulturendiversität. Die Nutzung des Ressourcenangebots (Nistplatz, Nahrung, Schutz) war abhängig von den Fortbewegungsmöglichkeiten. In großparzellig strukturierten Flächen mit geringer Kulturendiversität kam es häufig zu Revierverschiebungen und Reviervergrößerungen. Die Feldlerche versucht, im Laufe der Brutperiode den Getreideanteil im Revier zu verkleinern und Kulturen wie Rüben, Kartoffeln und auch Mais zu aquirieren. Die Nistplatzwahl zeigte eine deutliche Präferenz für alle nicht zu dicht stehenden, grasartigen Kulturen (Weizen, Hafer, Fettwiese). Eine Vegetationshöhe von 15–25 cm und eine Bodenbedeckung von 20–50 % bieten optimale Bedingungen für den Nestbau. 51 % aller Nester wurden in der Fettwiese angelegt, 20 % im Winterweizen und 18 % im Mais. Je nach Bewirtschaftungsart brüteten die im Mittel 2,4–2,8mal pro Brutsaison. Die Schlüpfrate von 220 Gelegen betrug 0,58. 44 % der geschlüpften Jungvögel verließen das Nest. Der Bruterfolg (nestverlassende Junge/gelegte Eier) lag bei max. 25 %. Dem Fütterungsverhalten der Altvögel nach zu schließen, wurden maximal 50 % der nestverlassenden Jungen flügge. Durchschnittlich war mit 0,9 flüggen Jungen pro Brutpaar und Jahr zu rechnen. Brutverluste waren kulturspezifisch und daher in erster Linie vom Neststandort abhängig.

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Territoriality and breeding biology of Skylark (Alauda arvensis) in an intensively farmed area in Switzerland

Summary In 1983–1987 four plots (total surface 307 ha) with up to 39 breeding pairs were studied in an area of intensive cultivation in the Swiss Lowlands (390 m asl). Distribution pattern and selection of territories are determined by a strong site tenacity of the birds. The size of territories averaged 3,3±0,9 hectares. It correlates negatively with the number of different crops per unit area and the diversity of cultures.The mobility within the vegetation determined which types of farmland ressources may be used for nesting, feeding and cover. Shifts of territories and attempts to enlarge them were frequent in areas of large plots with low crop diversity. During the season, Skylarks tried to reduce the proportion of cereal fields within their territory and to gain plots planted with sugar-beet, potatoes and corn.Their choice of nesting sites showed a strong preference for less dense grass crops such as wheat, oat or meadows. Optimal conditions for nest sites were in fields with a vegetation height of 15–25 cm and a ground coverage of 20–50 %. 51 % of 220 nests were constructed in heavily manured meadows, 20 % in winter wheat fields and 18 % in corn fields. Females bred on average 2,4–2,8 times per breeding season, depending on the type of cultivation (agriculture, husbandry). Hatching rate was 58 % out of 220 clutches, and 44 % of the hatched young left the nest. Maximum breeding success (i. e. young birds leaving the nest/number of eggs laid) was thus maximal 25 %. Observations of parental feeding behaviour suggest that a maximum of 50 % of the young larks which leave the nests survive to the age of fledging. It is estimated that 0,9 fledglings are raised per breeding pairs and year. Losses of broods vary according to farming practises in the different crops and therefore are largely depending on nesting sites.

     

Analysis of myosin light and heavy chain types in single human skeletal muscle fibers

In this study, myosin types in human skeletal muscle fibers were investigated with electrophoretic techniques. Single fibers were dissected out of lyophilized surgical biopsies and typed by staining for myofibrillar ATPase after preincubation in acid or alkaline buffers. After 14C-labelling of the fiber proteins in vitro by reductive methylation, the myosin light chain pattern was analysed on two-dimensional gels and the myosin heavy chains were investigated by one-dimensional peptide mapping. Surprisingly, human type I fibers, which contained only the slow heavy chain, were found to contain variable amounts of fast myosin light chains in addition to the two slow light chains LC1s and LC2s. The majority of the type I fibers in normal human muscle showed the pattern LC1s, LC2s and LC1f. Further evidence for the existence in human muscle of a hybrid myosin composed of a slow heavy chain with fast and slow light chains comes from the analysis of purified human myosin in the native state by pyrophosphate gel electrophoresis. With this method, a single band corresponding to slow myosin was obtained; this slow myosin had the light chain composition LC1s, LC2s and LC1f. Type IIA and IIB fibers, on the other hand, revealed identical light chain patterns consisting of only the fast light chains LC1f, LC2f and LC3f but were found to have different myosin havy chains. On the basis of the results presented, we suggest that the histochemical ATPase normally used for fibre typing is determined by the myosin heavy chain type (and not by the light chains). Thus, in normal human muscle a number of 'hybrid' myosins were found to occur, namely two extreme forms of fast myosins which have the same light chains but different heavy chains (IIA and IIB) and a continuum of slow forms consisting of the same heavy chain and slow light chains with a variable fast light chain composition. This is consistent with the different physiological roles these fibers are thought to have in muscle contraction.     

Conversion of dihydroorotate to orotate in parasitic protozoa.

The conversion of dihydroorotate to orotate, one of the key reactions in the de novo pyrimidine biosynthetic pathway, has been studied in a number of parasitic protozoa. Enzyme activities capable of carrying out this reaction were detected in six members of the Kinetoplastida (Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax, Trypanosoma lewisi, Trypanosoma cruzi, Leishmania enriettii) and three members of the genus Plasmodium (P. knowlesi, P. berghei, P. gallinaceum). The mechanism of the reaction in the two groups of protozoa were quite distinct. In the Kinetoplastida, the enzyme is an hydroxylase which occurs in the soluble fraction of the cell and probably requires tetrahydrobiopterin for activity. In contrast, in Plasmodium, the enzyme is a dehydrogenase which is particulate, probably mitochondrial, and intimately connected to the electron transport chain to which it passes electrons directly, probably at the ubiquinone level. Neither activity is regulated by fully formed pyrimidines. The enzyme in Plasmodium is similar in mechanism to the isofunctional mammalian enzyme. However, since malarial ubiquinones are apparently different from those in the mammal and since menoctone, which is active in vivo in experimental malaria, is a good inhibitor of the malarial enzyme, it could represent a useful target for chemotherapeutic attack. The enzyme in the Kinetoplastida is quite distinct from that in the mammal so that it too apparently falls into this category, though none of the currently used antitrypanosomal drugs appears to block it activity at physiological concentrations.     

Efficient removal of LoxP-flanked genes by electroporation of Cre-recombinase mRNA

Introduction of Cre-recombinase in target cells is currently achieved by transfection of plasmid DNA or by viral-mediated transduction. However, efficiency of non-viral DNA transfection is often low in many cell types, and the use of viral vectors for transduction implies a more complex and laborious manipulation associated with safety issues. We have developed a non-viral non-DNA technique for rapid and highly efficient excision of LoxP-flanked DNA sequences based on electroporation of in vitro transcribed mRNA encoding Cre-recombinase. A K562-DSRed[EGFP] cell line was developed in order to measure Cre-mediated recombination by flow cytometric analysis. These cells have a stable integrated DSRed reporter gene flanked by two LoxP sites, and an EGFP reporter gene, which could only be transcribed when the coding sequence for DSRed was removed. The presented data show recombination efficiencies, as measured by appearance of EGFP-fluorescence, of up to 85% in Cre-recombinase mRNA-electroporated K562-DSRed[EGFP] cells. In conclusion, mRNA electroporation of Cre-recombinase is a powerful, safe, and clinically applicable alternative to current technologies used for excision of stably integrated LoxP-flanked DNA sequences.     

European springtime temperature synchronises ibex horn growth across the eastern Swiss Alps

Direct effects of climate change on animal physiology, and indirect impacts from disruption of seasonal synchrony and breakdown of trophic interactions are particularly severe in Arctic and Alpine ecosystems. Unravelling biotic from abiotic drivers, however, remains challenging because high‐resolution animal population data are often limited in space and time. Here, we show that variation in annual horn growth (an indirect proxy for individual performance) of 8043 male Alpine ibex (Capra ibex) over the past four decades is well synchronised among eight disjunct colonies in the eastern Swiss Alps. Elevated March to May temperatures, causing premature melting of Alpine snowcover, earlier plant phenology and subsequent improvement of ibex food resources, fuelled annual horn growth. These results reveal dependency of local trophic interactions on large‐scale climate dynamics, and provide evidence that declining herbivore performance is not a universal response to global warming even for high‐altitude populations that are also harvested.