Ammoniten mit Kieferapparat und Radula aus Lias-Geschieben

Jaws and radula have been found in two adult microconch specimens of the Liassic ammonite speciesEleganticeras elegantulum (Young & Bird, 1828) from glacial drift boulders near Hamburg. They are more similar to those of recent dibranchiates than ofNautilus, the radula having seven longitudinal rows of teeth instead of thirteen in recentNautilus. Since bothOwens classification of the cephalopods into Dibranchiata and Tetrabranchiata according to the number of gills (which cannot be observed in fossil cephalopods) andSchwarz’ division into Ecto- and Endocochlia according to the (assumed) relative position of body and shell are rather unfortunate, the radula is suggested as a sound basis of classification. It is acceptable to paleo- as well as to neozoologists. As yet, the known evidence is sufficient for a twofold division only: Class Cephalopoda Subclass Lateradulata: Nautiloidea Subclass Angusteradulata: Ammonoidea Coleoidea     

Buchbesprechungen

Ohne Zusammenfassung     

In Vivo Substitution of Choline for Sodium Evokes a Selective Osmoinsensitive Increase of Extracellular Taurine in the Rat Hippocampus

Recent investigations have demonstrated that taurine and phosphoethanolamine (PEA) are the amino acids most sensitive to microdialysis-perfusion with reduced concentrations of NaCl. The aim of the present work was to assess the importance of Na+ deficiency in evoking this response. Further, the previously described selectivity of replacement of Cl- with acetate with respect to amino acid release was reinvestigated. The hippocampus of urethane-anesthetized rats was dialyzed with Krebs-Ringer bicarbonate buffer, and amino acid concentrations of the perfusate were determined. Choline chloride was then stepwise substituted for NaCl, and, in some cases, mannitol (122 mM) was included in low sodium-containing media. In other experiments, NaCl was replaced with sodium acetate. The dialysate levels of taurine increased selectively in response to Na+ substitution. The elevation of taurine was linearly related to the increase in choline chloride, and maximal levels amounted to 335% of basal levels. The increase in extracellular taurine was not inhibited by perfusion with medium made hyperosmotic with mannitol. Replacement of Cl- with acetate stimulated the release of taurine to 652% of resting levels. In addition, PEA levels increased to 250% of control concentration. Other amino acids were unaffected by Cl- substitution. The results show that taurine transport is considerably more sensitive to Na+ depletion than glutamate transport, which also is known to be Na+ dependent. The taurine increase evoked by low Na+ is not caused by cellular swelling as it was unaffected by hyperosmolar medium. Finally, substitution of acetate for Cl- causes a specific elevation of extracellular taurine and PEA, possibly as a result of cytotoxic edema.     

Crystallographic data for soybean hydrophobic protein

The soybean hydrophobic protein belongs to a family of proteins that contains a number of storage and phospholipid binding proteins. Its function is not known, but its overall hydrophobic nature is typical of many membrane proteins of similar size. The molecular weight is 8.3 x 10(3), and it crystallizes in the space group P2(1)2(1)2(1), with a = 52.01 A, b = 43.50 A and c = 28.80 A. The crystals diffract to 1.8 A resolution, and are thus suitable for X-ray structural studies.     

Design of a bubble-swawm bioreactor for animal cell culture

A stationary bubble-swarm has been used to aerate a mammalian cell culture bioreactor with an extremely low gas flow rate. Prolonging the residence time of the gas bubbles within the medium improved the efficiency of the gas transfer into the liquid phase and suppressed foam formation. An appropriate field of speed gradients prevented the bubbles from rising to the surface. This aeration method achieves an almost 90% transfer of oxygen supplied by the bubbles. Consequently, it is able to supply cells with oxygen even at high cell densities, while sparging with a gas flow of only 0.22·10^–3–1.45·10^–3 vvm (30–200 ml/h).The reactor design, the oxygen transfer rates and the high efficiency of the system are presented. Two repeated batch cultures of a rat-mouse hybridoma cell line are compared with a surface-aerated spinner culture. The used cell culture medium was serum-free, either with or without BSA and did not contain surfactants or other cell protecting agents. One batch is discussed in detail for oxygen supply, amino acid consumption and specific antibody production.     

Distribution and conservation of sequences homologous to the 1731 retrotransposon in Drosophila

The distribution of 1731 retrotransposon-hybridizing sequences in the family Drosophilidae has been studied using a 1731 probe from Drosophila melanogaster. Squash blot and Southern blot analyses of 42 species reveal that the 1731 sequences are widespread within both the Sophophora and Drosophila subgenera and are also present in the genera Scaptomyza and Zaprionus. Hence the 1731 retrotransposon family appears to have a long evolutionary history in the Drosophilidae genome. Differences of hybridization signal intensity suggested that the 1731 sequence is well conserved only in the three species most closely related to D. melanogaster (D. simulans, D. mauritiana, and D. sechellia). A survey of insertion sites in numerous different populations of the previous four species by in situ hybridization to polytene chromosomes has shown in all cases both chromocentric hybridizations and a low number of sites (0-5) on the chromosomal arms. This number of sites is among the lowest observed in D. melanogaster and D. simulans when 1731 is compared with other retrotransposon families. In addition, we have observed species-specific patterns of the chromocentric hybridization signal, suggesting rapid modifications of the beta-heterochromatin components since the radiation of the melanogaster subgroup.      

Ecdysone regulation of the Drosophila Sgs-4 gene is mediated by the synergistic action of ecdysone receptor and SEBP 3.

The steroid hormone 20-hydroxyecdysone controls both induction and repression of the Drosophila 'intermolt gene' Sgs-4. We show here that the ecdysone receptor binds to two sites, element I and element II, in the regulatory region of Sgs-4. A functional analysis revealed that element II appears to be of no importance for Sgs-4 expression, while element I proved to be an ecdysone response element that is necessary, but not sufficient, for induction of Sgs-4 expression. Our results provide no evidence that repression of Sgs-4 expression is mediated by one of the two receptor binding sites. In the close vicinity of elements I and II, we detected two binding sites of secretion enhancer binding protein 3 (SEBP 3). Like receptor element I, one of these sites also proved to be necessary, but not sufficient, for expression of Sgs-4. Therefore, induction of Sgs-4 requires binding of both ecdysone receptor and SEBP 3 to a complex hormone response unit, which also contains binding sites for a third factor, SEBP 2. The SEBP 2 sites coincide with binding sites of products of the Broad-Complex locus, which has been implicated recently with transduction of the hormonal signal. Thus, the available data suggest that induction of Sgs-4, and possibly other 'intermolt genes', is a combination of a primary and a secondary response to the hormone.     

Hot Spots of Recombination in Fission Yeast: Inactivation of the M26 Hot Spot by Deletion of the Ade6 Promoter and the Novel Hotspot Ura4-Aim

The M26 mutation in the ade6 gene of Schizosaccharomyces pombe creates a hot spot of meiotic recombination. A single base substitution, the M26 mutation is situated within the open reading frame, near the 5' end. It has previously been shown that the heptanucleotide sequence 5' ATGACGT 3', which includes the M26 mutation, is required for hot spot activity. The 510-bp ade6-delXB deletion encompasses the promoter and the first 23 bp of the open reading frame, ending 112 bp upstream of M26. Deletion of the promoter in cis to M26 abolishes hot spot activity, while deletion in trans to M26 has no effect. Homozygous deletion of the promoter also eliminates M26 hot spot activity, indicating that the heterology created through deletion of the promoter per se is not responsible for the loss of hot spot activity. Thus, DNA sequences other than the heptanucleotide 5' ATGACGT 3', which must be located at the 5' end of the ade6 gene, appear to be required for hot spot activity. While the M26 hotspot stimulates crossovers associated with M26 conversion, it does not affect the crossover frequency in the intervals adjacent to ade6. The flanking marker ura4-aim, a heterology created by insertion of the ura4(+) gene upstream of ade6, turned out to be a hot spot itself. It shows disparity of conversion with preferential loss of the insertion. The frequency of conversion at ura4-aim is reduced when the M26 hot spot is active 15 kb away, indicating competition for recombination factors by hot spots in close proximity.