Ecophysiology of Aufwuchs-eating cichlids in Lake Tanganyika: niche separation by trophic specialization

Synopsis The Aufwuchs-eating cichlids of Lake Tanganyika show clear trophic differences that are correlated to their morphology, physiology and foraging behaviour. The species are grouped into three categories of relative intestinal length according to their feeding habits. A correlation between the intestinal length and the diet could be demonstrated, ranging from around 2.5 for species ingesting more animal food, to 7.8 for detritivorous and microalgivorous species. The relative intestinal length of domesticTropheus moorii, raised in aquaria was significantly lower than that of wild individuals by a factor of 1.7, demonstrating a wide range of phenotypic adaptability. The activities of trypsin and amylase were at an equal level in four Aufwuchseating species, but the activity of laminarinase of a detritivorous-microalgivorous species (Petrochromis orthognathus) was 2.6 times higher than that of an algivorous species (Tropheus moorii). The laminarinase seems to be an excellent marker enzyme for detritivorous or microalgivorous feeding.     

Sensory modulation and behavioral choice during feeding in the Australian frog, Cyclorana novaehollandiae

This study investigates how visual and tactile sensory information, as well as biomechanical effects due to differences in physical characteristics of the prey, influence feeding behavior in the frog Cyclorana novaehollandiae. Video motion analysis was used to quantify movement patterns produced when feeding on five prey types (termites, waxworms, crickets, mice and earthworms). Twelve kinematic variables differed significantly among prey types, and twelve variables were correlated with prey characteristics (including mass, length, height and velocity of movement). Results indicate that C.␣novaehollandiae uses a different strategy to capture each prey type. Visual assessment of prey characteristics appeared to be more important in modulating feeding behavior than tactile cues or biomechanical effects. We propose a hierarchical hypothesis of behavioral choice, in which decisions are based primarily on visual analysis of prey characteristics. In this model, the frogs first choose between jaw prehension and tongue prehension based on prey size. If they have chosen jaw prehension, they next choose between upward or downward head rotation based on length and height of the prey. If they have chosen tongue prehension, they next choose between behavior for fast and slow prey. Final decisions may be the result of behavioral fine tuning based on tactile feedback. Accepted: 5 August 1996     

Primary Structure of Myostracal Prism Soluble Protein (MPSP) in Oyster Shell, Crassostrea gigas

Soluble protein (MPSP, myostracal prism soluble protein) obtained from myostracum in oyster shell (Crassostrea gigas) was characterized using biochemical and molecular biological techniques. From an analysis of secondary protein structure, it was shown that β-structure was predominant in MPSP. And via in vitro assays, the relation of MPSP to biomineral phase and morphology was studied. SDS-PAGE revealed one major protein band of 20 kDa. An amino acid sequence of 160 amino acids was deduced for myostracum by characterization of the complementary DNA encoding the protein. The deduced protein was composed of a high proportion of Gly and Asp, typifying a calcium-binding protein for shell formation, and a relatively high proportion of Val, Ala and Ile, typifying an adhesive protein. In contrast to prevailing expectations, (Gly–Asp)n-type sequence motifs exist in MPSP, demanding a revision of previous theories of protein–mineral interactions. The cDNA sequence of myostracum is elucidated for the first time.     

Ribosome stacking defines CGS1 mRNA degradation sites during nascent peptide-mediated translation arrest

Expression of the Arabidopsis CGS1 gene that codes for cystathionine gamma-synthase is feedback-regulated at the step of mRNA degradation in response to S-adenosyl-L-methionine (AdoMet). This regulation occurs during translation and involves AdoMet-induced temporal translation arrest prior to the mRNA degradation. Here, we have identified multiple intermediates of CGS1 mRNA degradation with different 5' ends that are separated by approximately 30 nucleotides. Longer intermediates were found to be produced as the number of ribosomes loaded on mRNA was increased. Sucrose density gradient centrifugation experiments showed that the shortest mRNA degradation intermediate was associated with monosomes, whereas longer degradation intermediates were associated with multiple ribosomes. Immunoblot analyses revealed a ladder of premature polypeptides whose molecular weights corresponded to products of ribosomes in a stalled stack. An increase in smaller premature polypeptides was observed as the number of ribosomes loaded on mRNA increased. These results show that AdoMet induces the stacking of ribosomes on CGS1 mRNA and that multiple mRNA degradation sites probably correspond to each stacked ribosome.     

Chromosome mapping of low-temperature induced Wcs120 family genes and regulation of cold-tolerance expression in wheat

 Low-temperature (LT) induced genes of the Wcs120 family in wheat (Triticum aestivum) were mapped to specific chromosome arms using Western and Southern blot analysis on the ditelocentric series in the cultivar Chinese Spring (CS). Identified genes were located on the long arms of the homoeologous group 6 chromosomes of all 3 genomes (A, B, and D) of hexaploid wheat. Related species carrying either the A, D, or AB genomes were also examined using Southern and Western analysis with the Wcs120 probe and the WCS120 antibody. All closely related species carrying one or more of the genomes of hexaploid wheat produced a 50 kDa protein that was identified by the antibody, and a Wcs120 homoeologue was detected by Southern analysis in all species. In the absence of chromosome arm 6DL in hexaploid CS wheat no 50 kDa protein was produced and the high-intensity Wcs120 band was missing, indicating 6DL as the location of Wcs120 but suggesting silencing of the Wcs120 homoeologue in the A genome. Levels of proteins that cross-reacted with the Wcs120 antibody and degrees of cold tolerance were also investigated in the Chinese Spring/Cheyenne (CS/CNN) chromosome substitution series. CNN chromosome 5A increased the cold tolerance of CS wheat. Densitometry scanning of Western blots to determine protein levels showed that the group 5 chromosome 5A had a regulatory effect on the expression of the Wcs120 gene family located on the group 6 chromosomes of all three hexaploid wheat genomes. Received: 10 July 1996 / Accepted: 30 September 1996     

Differential expression of annexin V during spermatogenesis in the newt Cynops pyrrhogaster

 In order to isolate genes whose expression is up-regulated after the initiation of meiosis, we screened a cDNA expression library of newt testes with antiserum against homogenates of testes derived from the spermatogonial and spermatocyte stages. We report the isolation of spermatocyte-specific cDNA clones encoding a newt homologue of the calcium-dependent phospholipid-binding protein, annexin V. Northern blot analysis showed that newt annexin V mRNA was 1.7 kb in length and was expressed strongly in testes, but weakly in other organs. In situ hybridization revealed that the expression of newt annexin mRNA was barely observed in spermatogonia, but increased significantly in leptotene-zygotene primary spermatocytes and reached a maximum level in pachytene spermatocytes and round spermatids. The newt annexin V cDNA predicted a 323-amino acid protein and had a 68% homology to human annexin V. The predicted amino acid sequence contained a conserved 4-fold internal repeat of approximately 70 residues like other annexin proteins. Immunoblot analysis using the monoclonal antibody against newt annexin V showed that the protein was expressed scarcely in spermatogonia but was abundantly expressed in stages from primary spermatocytes to spermatids; this pattern was consistent to that of the mRNA. Immunohistochemical analysis revealed that newt annexin V was localized in the cytoplasm of the spermatogenic cells, but not in somatic cells such as Sertoli cells or pericystic cells. These results indicate that the expression of newt annexin V is up-regulated in the spermatogenic cells after the initiation of meiosis and suggest that newt annexin V plays an important role in spermatogenesis. Received: 8 December 1995 / Accepted: 12 February 1996 Edited by H. Shimada/D. Tautz     

Hox C6 expression during development and regeneration of forelimbs in larval Notophthalmus viridescens

 A central theme concerning the epimorphic regenerative potential of urodele amphibian appendages is that limb regeneration in the adult parallels larval limb development. Results of previous research have led to the suggestion that homeobox containing genes are ”re-expressed” during the epimorphic regeneration of forelimbs of adult Notophthalmus viridescens in patterns which retrace larval limb development. However, to date no literature exists concerning expression patterns of any homeobox containing genes during larval development of this species. The lack of such information has been a hindrance in exploring the similarities as well as differences which exist between limb regeneration in adults and limb development in larvae. Here we report the first such results of the localization of Hox C6 (formerly, NvHBox-1) in developing and regenerating forelimbs of N. viridescens larvae as demonstrated by whole-mount in situ hybridization. Inasmuch as the pattern of Hox C6 expression is similar in developing forelimb buds of larvae and epimorphically regenerating forelimb blastemata of both adults and larvae, our results support the paradigm that epimorphic regeneration in adult newts parallels larval forelimb development. However, in contrast with observations which document the presence of Hox C6 in both intact, as well as regenerating hindlimbs and tails of adult newts, our results reveal no such Hox C6 expression during larval development of hindlimbs or the tail. As such, our findings indicate that critical differences in larval hindlimb and tail development versus adult expression patterns of this gene in these two appendages may be due primarily to differences in gene regulation as opposed to gene function. Thus, the apparent ability of urodeles to regulate genes in such a highly co-ordinated fashion so as to replace lost, differentiated, appendicular structures in adult animals may assist, at least in part, in better elucidating the phenomenon of epimorphic regeneration. Received: 6 November 1998 / Accepted: 12 December 1998     

Inducible ternary control of transgene expression and cell ablation in Drosophila

 In Drosophila, P-GAL4 enhancer trap lines can target expression of a cloned gene, under control of a UAS_GAL element, to any cells of interest. However, additional expression of GAL4 in other cells can produce unwanted lethality or side-effects, particularly when it drives expression of a toxic gene product. To target the toxic gene product ricin A chain specifically to adult neurons, we have superimposed a second layer of regulation on the GAL4 control. We have constructed flies in which an effector gene is separated from UAS_GAL by a polyadenylation site flanked by two FRT sites in the same orientation. A recombination event between the two FRT sites, catalysed by yeast FLP recombinase, brings the effector gene under control of UAS_GAL. Consequently, expression of the effector gene is turned on in that cell and its descendants, if they also express GAL4. Recombinase is supplied by heat shock induction of a FLP transgene, allowing both timing and frequency of recombination events to be regulated. Using a lacZ effector (reporter) to test the system, we have generated labelled clones in the embryonic mesoderm and shown that most recombination events occur soon after FLP recombinase is supplied. By substituting the ricin A chain gene for lacZ, we have performed mosaic cell ablations in one GAL4 line that marks the adult giant descending neurons, and in a second which marks mushroom body neurons. In a number of cases we observed loss of one or both the adult giant descending neurons, or of subsets of mushroom body neurons. In association with the mushroom body ablations, we also observed misrouting of surviving axons. Received: 17 December 1995 / Accepted: 6 March 1996 Edited by M. Akam     

Biochemical and immunological changes on oral glutamate feeding in male albino rats

 High altitude stress leads to lipid peroxidation and free radical formation which results in cell membrane damage in organs and tissues, and associated mountain diseases. This paper discusses the changes in biochemical parameters and antibody response on feeding glutamate to male albino Sprague Dawley rats under hypoxic stress. Exposure of rats to simulated hypoxia at 7576 m, for 6 h daily for 5 consecutive days, in an animal decompression chamber at 32±2° C resulted in an increase in plasma malondialdehyde level with a concomitant decrease in blood glutathione (reduced) level. Supplementation of glutamate orally at an optimal dose (27 mg/kg body weight) in male albino rats under hypoxia enhanced glutathione level and decreased malondialdehyde concentration significantly. Glutamate feeding improved total plasma protein and glucose levels under hypoxia. The activities of serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) and the urea level remained elevated on glutamate supplementation under hypoxia. Glutamate supplementation increased the humoral response against sheep red blood cells (antibody titre). These results indicate a possible utility of glutamate in the amelioration of hypoxia-induced oxidative stress. Received: 23 March 1998 / Accepted: 19 October 1998     

Segment-specific expression of the gap junction gene connexin31 during hindbrain development

 During segmentation of the mouse hindbrain (d8.0–8.5 pc), expression of the gap junction gene connexin31 (cx31) is precisely restricted to rhombomeres (r) 3 and 5. Shortly afterwards, during the turning process, cx31 expression in rhombomere 3 decreases and is no longer detectable at d9.5 pc, whereas expression in rhombomere 5 is maintained until about d10.0 pc. So far, cx31 is the first gap junction gene found to be expressed in rhombomeres. Its precise segmental and temporal expression pattern may reflect a critical requirement of cx31 channels for these odd numbered rhombomeres to acquire distinct cell identities. Received: 9 June 1997 / Accepted: 30 July 1997     

The molybdenum site in the xanthine oxidase-related aldehyde oxidoreductase from Desulfovibrio gigas and a catalytic mechanism for this class of enzymes

 The crystal structure analysis of the aldehyde oxidoreductase from Desulfovibrio gigas was exceptionally revealing with regard to the ligands and structure of the molybdenum site and the mechanism of the hydroxylation reaction catalyzed. The metal is pentacoordinated by two sulfurs of the cis–dithiolene group of the molybdopterin cofactor and by facially arranged sulfido, oxo and water ligands. The latter is in hydrogen-bonding contact with the carboxylate group of Glu 869 and the hydroxyl group of an isopropanol molecule, a substrate analogue inhibitor. This steric arrangement strongly suggests a mechanism for the reductive half-cycle of the reaction with Glu 869 as the base, the metal-bound water as the source of the transferred hydroxyl group, and the sulfido group as the hydride acceptor. The geometry and the proposed mechanism are in agreement with density functional calculations on a model of the molybdenum site. In the oxidative half-reaction, electrons are withdrawn from Mo^rv through the rigidly held pterin ring system, via the iron-sulfur clusters, to the protein surface. Received: 25 June 1997 / Accepted: 20 August 1997