Evidence for rapid faunal changes on islands in a man-made lake

Summary Few studies of island biogeography have been made on islands in which the time of insularization is precisely known. We tested the effects of island formation on ant species diversity in a man-made lake in South Africa, to determine whether island effects are detectable after only 16 years of insularization. The number of ant species observed at trap-line censuses on islands was significantly correlated with island size (r=0.608; P<0.05) and ant species diversity was generally low compared with similar mainland habitats. Mean species number for all islands, including landbridge islands, was 5.5±3.3 species, and on mainland sites was 7.9±2.85 species. Island effects were more marked on islands <20 ha, which had a mean of 3.3±2.5 species per island. Species number on islands was inversely related to densities of the aggressive Anoplolepis custodiens and A. steingroeveri. These two species were only patchily distributed on mainlands, but these ants were nearly ubiquitous on small islands. Several lines of evidence suggest that this single species domination may be responsible for island effects. Island sites also differed in the number of ant species in different trophic groupings, tending to have fewer granivorous species than the mainland sites, but species in other diet groups were similar in both island and mainland habitats. We conclude that there have been marked changes in the ant faunas on islands smaller than 20 ha apparently due to changes in abundance of the dominant ant species. However, the causes of these changes are unknown.     

ERD2, a yeast gene required for the receptor-mediated retrieval of luminal ER proteins from the secretory pathway

Resident proteins of the ER lumen carry a specific tetrapeptide signal (KDEL or HDEL) that prevents their secretion. We have previously described the isolation of yeast mutants that fail to retain such resident proteins within the cell. Here we describe ERD2, a gene required for retention. It encodes a 26 kd integral membrane protein whose abundance determines the efficiency and capacity of the retention system. Reduced expression of ERD2 leads to secretion of proteins bearing the HDEL signal, whereas overexpression of ERD2 improves retention both in wild-type cells and in other mutants. These results are consistent with other evidence that ERD2 encodes the HDEL receptor (see accompanying paper). The gene is also required, perhaps indirectly, for normal protein transport through the Golgi, and hence for growth. We discuss possible roles for ERD2 in the secretory pathway.     

Monoclonal antibodies to the murine zona pellucida protein with sperm receptor activity: effects on fertilization and early development

During development and maturation, mammalian oocytes are surrounded by the zona pellucida which in the mouse is comprised of three sulfated glycoproteins, ZP-1, ZP-2, and ZP-3. Previously, monoclonal antibodies to ZP-2 have been isolated. The isolation and characterization of monoclonal antibodies specific for ZP-3, the zona protein with sperm receptor activity are now reported. Following passive immunization, these monoclonal antibodies localize to the intraovarian zonae pellucidae and their presence precludes both in vivo and in vitro fertilization of subsequently ovulated eggs. Monoclonal antibodies specific for either ZP-2 or ZP-3 also completely block in vitro fertilization at relatively low concentration ranging from 0.4 to 75 micrograms/ml. The contraceptive effect requires the presence of the zona and appears to inhibit the penetration of the zona pellucida by sperm rather than by blocking the sperm binding site. Neither antibody interferes with in vitro development from the two-cell to the blastocyst stage or with subsequent hatching from the enveloping zona pellucida.     

Cell-free translation of mitochondrial nicotinamide nucleotide transhydrogenase

Mammalian nicotinamide nucleotide transhydrogenase is translated as a 5000 daltons larger molecular weight precursor in a cell-free system programmed with rat liver polysomes. The mature rat liver enzyme had the same molecular weight as the purified beef heart enzyme, 115 000 daltons. The precursor was not processed in vitro by liver mitochondria or by a rat liver mitochondrial matrix fraction, nor did it appear to bind to mitochondria. In contrast, pre-FeS protein of the cytochrome bc₁ complex was processed in the same samples by both mitochondria and matrix, suggesting an important difference in the processing mechanisms or in the efficiency of processing of the two precursors.     

Differential expression of the eight genes of the petunia ribulose bisphosphate carboxylase small subunit multi-gene family

Of the eight nuclear genes in the plant multi-gene family which encodes the small subunit (rbcS) of Petunia (Mitchell) ribulose bisphosphate carboxylase, one rbcS gene accounts for 47% of the total rbcS gene expression in petunia leaf tissue. Expression of each of five other rbcS genes is detected at levels between 2 and 23% of the total rbcS expression in leaf tissue, while expression of the remaining two rbcS genes is not detected. There is considerable variation (500-fold) in the levels of total rbcS mRNA in six organs of petunia (leaves, sepals, petals, stems, roots and stigmas/anthers). One gene, SSU301, showed the highest levels of steady-state mRNA in each of the organs examined. We discuss the differences in the steady-state mRNA levels of the individual rbcS genes in relation to their gene structure, nucleotide sequence and genomic linkage.     

The Conversion of Nitrite to Nitrogen Oxide(s) by the Constitutive NAD(P)H-Nitrate Reductase Enzyme from Soybean

A two-step purification protocol was used in an attempt to separate the constitutive NAD(P)H-nitrate reductase [NAD(P)H-NR, pH 6.5; EC 1.6.6.2] activity from the nitric oxide and nitrogen dioxide (NO_(x)) evolution activity extracted from soybean (Glycine max [L.] Merr.) leaflets. Both of these activities were eluted with NADPH from Blue Sepharose columns loaded with extracts from either wild-type or LNR-5 and LNR-6 (lack constitutive NADH-NR [pH 6.5]) mutant soybean plants regardless of nutrient growth conditions. Fast protein liquid chromatography-anion exchange (Mono Q column) chromatography following Blue Sepharose affinity chromatography was also unable to separate the two activities. These data provide strong evidence that the constitutive NAD(P)H-NR (pH 6.5) in soybean is the enzyme responsible for NO_(x) formation. The Blue Sepharose-purified soybean enzyme has a pH optimum of 6.75, an apparent K_m for nitrite of 0.49 millimolar, and an apparent K_m for NADPH and NADH of 7.2 and 7.4 micromolar, respectively, for the NO_(x) evolution activity. In addition to NAD(P)H, reduced flavin mononucleotide (FMNH₂) and reduced methyl viologen (MV) can serve as electron donors for NO_(x) evolution activity. The NADPH-, FMNH₂-, and reduced MV-NO_(x) evolution activities were all inhibited by cyanide. The NADPH activity was also inhibited by p-hydroxymer-curibenzoate, whereas, the FMNH₂ and MV activities were relatively insensitive to inhibition. These data indicate that the terminal molybdenum-containing portion of the enzyme is involved in the reduction of nitrite to NO_(x). NADPH eluted both NR and NO_(x) evolution activities from Blue Sepharose columns loaded with extracts of either nitrate- or zero N-grown winged bean (Psophocarpus tetragonolobus [L.]), whereas NADH did not elute either type of activity. Winged bean appears to contain only one type of NR enzyme that is similar to the constitutive NAD(P)H-NR (pH 6.5) enzyme of soybean.     

亚硒酸钠抗红细胞膜蛋白交联作用的机理探讨

邻苯二酚氧化处理人红细胞膜会导致膜蛋白交联,产生高分子聚合物(HMP)。用N—乙基马来酰胺(NEM)封闭膜蛋白硫基,则不产生HMP。预先用Na SeO_3(0.05mol/L)处理红细胞膜,也同样不产生HMP。用N—(3-芘)马来酰胺(N-〔3-P〕NEM)标记红细胞膜来测试不同浓度Na_2SeO_3对荧光强度的影响。结果表明,随着Na SeO_3浓度增高荧光强度相应降低。Na_2SeO_3对红细胞膜的预处理时间和荧光强度的变化有关。经Na SeO_3处理的红细胞膜ESR谱提示了Na_2SeO_3与材相互作用有关。用荧光法测定膜结合硒含量表明,Na_2SeO_3处理红细胞膜可导致膜结合硒含量增高。推测,Na SeO_3很可能与膜蛋白疏基作用形成结合硒,从而起到抗膜蛋白交联作用。     

Roles for the integrin VLA-4 and its counter receptor VCAM-1 in myogenesis.

Mammalian myogenesis is biphasic: primary myoblasts fuse to form primary myotubes, then secondary myoblasts align along the primary myotubes and form secondary myotubes, which comprise most of adult muscle. We provide evidence that an integrin (VLA-4) and its counter receptor (VCAM-1) have a role in secondary myogenesis. Both receptors are synthesized by cultured muscle cells: VLA-4 is induced as myotubes form, whereas VCAM-1 is present on myoblasts and myotubes. In vivo, both molecules are expressed at sites of secondary myogenesis, VLA-4 on primary and secondary myotubes, and VCAM-1 on secondary myoblasts and on regions of secondary myotubes apposed to primary myotubes. These patterns suggest that VLA-4-VCAM-1 interactions influence alignment of secondary myoblasts along primary myotubes and/or the fusion of secondary myoblasts. In support of the latter possibility, antibodies to VLA-4 or VCAM-1 inhibit myotube formation in culture.