Modelling Annual Numbers of Bird Territories on Farmland Plots

The Common Birds Census of the British Trust for Ornithology provides extensive data from which it is possible to attempt to explain some aspects of the population dynamics of common bird species. Such data are examined here. A consistent, striking feature of the data is noted when a second order model is fitted to estimated numbers of territory-holding birds in successive years. Alternative approaches to explaining the observed nature of the data are presented, including the development of simple birth-death-maturation (-immigration) models.     

Some effects of 5-bromodeoxyuridine on polyoma-transformed mouse cells

The tumor-forming potential of polyoma-transformed mouse cells was found to be diminished but not eliminated after growth in the presence of 5-bromodeoxyuridine (BUdR). Several in vitro characteristics of the cells were also investigated and those which best correlated with the tumor studies were the ability to form colonies either in agar suspension or on monolayers of non-transformed cells. Transformed cells treated with BUdR grew well in culture when plated above a certain critical number of cells per unit area and poorly when plated at lower densities. Non-transformed cells exposed to BUdR for two or three passages were unable to divide.     

A cysteine proteinase cDNA from Trypanosoma brucei predicts an enzyme with an unusual C-terminal extension

A cDNA for a Trypanosoma brucei cysteine proteinase has been cloned and sequenced. The deduced protein can be divided into four domains, based on homologies with other cysteine proteinases: the pre-, pro- and central regions show considerable homology to the cathepsin L class of mammalian enzymes, whilst the long C-terminal extension distinguishes the trypanosome enzyme from all mammalian cysteine proteinases reported. This 108 amino acid extension, which includes 9 contiguous prolines near the junction with the central domain, appears likely to be processed in part to produce the mature enzyme, and may be involved in targeting the protein within the cell. The trypanosome genome contains more than 20 copies of the cysteine proteinase gene arranged in a long tandem array.     

Single-step isolation and sequencing of vasopressin and oxytocin precursors.

The pre- and post-Golgi processing of preprovasopressin and prepro-oxytocin was evaluated by microsequencing for incorporated radiolabel. 35S-Cysteine and 3H-fucose were microinjected into rat supraoptic nuclei (SON), and proteins and peptides related to the biosynthesis of vasopressin (VP) and oxytocin (OT) were isolated at various times from the supraoptic nuclei and neural lobe by employing a one-step procedure of high performance liquid chromatography (HPLC). These proteins and peptides were recognized through their binding to specific antibodies against VP, OT, and rat neurophysins (RNPs), and by their binding to ConA-Sepharose. Two immunoreactive glycoproteins related to VP biosynthesis were recovered from the SON and both contained fucose and had a 35S-cysteine placement consistent with the location of the hormone sequence at the N-terminus. SDS-electrophoresis revealed the major protein form to be 21,000 daltons and the minor protein form to be 19,000 daltons. One nonglycosylated protein of 16,000 daltons related to oxytocin biosynthesis was recovered from the SON, and this protein also had a 35S-cysteine placement consistent with an N-terminal OT sequence. These data provide the first sequential evidence that prior to, or shortly after, packaging in the Golgi the preprohormones of VP and OT have lost their entire leader-peptide structures.     

Contrasting membrane localization and behavior of halogenated cyclobutanes that follow or violate the Meyer-Overton hypothesis of general anesthetic potency.

The membrane localization and properties of two halogenated cyclobutanes were examined using 2H and 19F NMR. The common predictors of potency indicate that these two compounds will have anesthetic activity; however, 1,2-dichlorohexafluorocyclobutane (c(CCIFCCIFCF2CF2)) is not an effective anesthetic, whereas 1-chloro-1,2,2-trifluorocyclobutane (c(CCIFCF2CH2CH2)) is an effective general anesthetic. Using 2H NMR, the effect of these compounds on the acyl chain packing in palmitoyl (d31) oleoylphosphatidylcholine membranes was examined. The addition of the anesthetic c(CCIFCF2CH2CH2) results in small increases in the segmental order near the headgroup, whereas segments deeper in the bilayer show decreases in order. These results are consistent with those obtained previously for halothane, isoflurane, and enflurane. On the addition of the nonanesthetic c(CCIFCCIFCF2CF2), the segmental order in vitually unchanged, except for a slightly changed order near the segents 10-12 of the palmitoyl chains. These results, and the 19F chemical shifts, indicate that the anesthetic c(CCIFCF2CH2CH2) exhibits a preference for the membrane interface, as do the other general anesthetics, whereas the nonanesthetic c(CCIFCIFCF2CF2) resides within the membrane hydrocarbon core. The compound c(CCIFCCIFCF2CF2) and other nonanesthetic halocarbons have lower molecular dipole moments compared to effective anesthetic halocarbons, which may account for their altered distribution within the membrane. These data strongly suggest that preferential localization of a halocarbon within the membrane interface is a predictor of anesthetic potency. Furthermore, the data indicate that the properties and forces in the membrane interface deserve consideration as mediators of anesthetic activity.     

The apolipoprotein B gene is constitutively expressed in HepG2 cells: regulation of secretion by oleic acid, albumin, and insulin, and measurement of the mRNA half-life

The objective of this study was to establish conditions whereby apoB secreted from HepG2 cells could be regulated over a wide range, and to determine whether changes of output were correlated with the level of apoB mRNA. The presence of oleate (complexed to 3% albumin at a molar ratio of 1.7:1) resulted in a 3.5-fold stimulation of apoB secretion that was apparent after only 3 h. Insulin halved the rate of apoB output and the inhibition was detectable within the physiological insulin range, but was not apparent until 12-16 h. Albumin in the culture medium had a dose-dependent inhibitory effect on apoB production. Overall, apoB secretion from HepG2 cells was modulated over a 7-fold range. However, when apoB mRNA was assayed by slot-blot hybridization, no change was detectable under any of the conditions that modulated apoB output. Quantitative solution hybridization was used to confirm that oleate did not affect the level of apoB mRNA. Kinetic analysis of the decay of [3H]uridine-labeled apoB mRNA showed that the half-life of apoB mRNA was 16 h. We conclude from these studies that the apoB gene is constitutively expressed in HepG2 cells and that the mechanism of acute regulation of apoB production by these cells must involve co- or post-translational processes.     

The diet of largemouth bass, Micropterus salmoides, in Lake Naivasha, Kenya

Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. Of these, Oreochromis leucostictus, Tilapia zillii and Micropterus salmoides (largemouth black bass) support an important gillnet fishery with bass also being taken for sport. Until bass reached 260 mm f.l. they depended upon invertebrate food organisms. Thereafter crayfish, fish and frogs became increasingly important the larger the size of the bass. The most important invertebrate prey species was the water boatman, Micronecta scutellaris , followed by chironomid and culicid pupae. Zooplank-ton was consumed but only in large quantity by fish smaller than 80 mm. For bass over 260 mm the crayfish, Procambarus darkii , was the principal food. The largemouth bass in Lake Naivasha are generalized macro-predators, feeding principally on free-living animals of a kind most likely to be found in the littoral zones.