Vergleichende Untersuchungen zum Kontaktverhalten verschiedener Arten der Gattung Tilapia (Cichlidae,Pisces) und ihrer Bastarde

• 1 Tilapia tholloni (Substratbrüter), T. nilotica (weiblicher Maulbrüter) und T. heudeloti macrocephala (männlicher Maulbrüter) wurden künstlich erbrütet und ihre angeborenen Kontaktreaktionen in standardisierten Attrappenversuchen untersucht.
• 2 Das Kontaktverhalten muß während einer kritischen Phase (bei T. nilotica unter den angegebenen Versuchsbedingungen bis ungefähr zum 21. Tag nach dem Ablaichen) aktiviert werden, wenn es längere Zeit andauern soll (= Reaktionsphase). Die Reaktionsphase kann bei T. nilotica mehrere Wochen dauern. In ihr nimmt die Reaktionsstärke (Anzahl und Dauer der Kontakte) zunächst rasch zu, erreicht ein Maximum und nimmt dann allmählich wieder ab. Anstieg, Maximum und Abnahme sind an bestimmte Entwicklungsabschnitte gebunden, weitgehend unabhängig davon, ob die Tiere zuvor schon Kontaktverhalten geäußert haben oder nicht. Die Kontaktreaktionen unterscheiden sich u. a. durch die Dauer der Kontakte: tholloni = 0,7 Sek., nilotica = 86,5 Sek., heudeloti m. = 1,5 Sek. je Tag und Tier (Maximalwerte bei bestimmten, für alle Arten gleichen Versuchsbedingungen).
• 3 Von der Aufzuchttemperatur hängt es ab, in welchem Entwicklungsabschnitt die Reaktionsphase liegt. Das Reaktionsmaximum junger T. nilotica lag bei 24° C am 9., bei 29° C am Tag nach der Eiablage.
• 4 Geblendete nilotica-Jungfische zeigten nur zu Beginn der Reaktionsphase schwaches Kontaktverhalten, normale Tiere äußerten gegenüber einer durchsichtigen Glasattrappe abgeschwächtes, nur kurze Zeit dauerndes Kontaktverhalten. Das Kontaktverhalten wird durch mechanische (Strömung) und optische Reize ausgelöter und gesteuert.
• 5 Junge Maulbrüter aus kleinen Eiern erreichten eine längere Kontaktdauer als solche aus größeren. Nach künstlicher Reduktion der Dottermenge um 10–20%) erhöhte sich die Kontaktdauer bei jungen nilotica um 23,1%, die Zahl der Kontakte nahm gleichzeitig um 7,6% ab. Die ♀♀ der substratbrütenden T. mariae legen große Eier, die Jungen zeigten gegenüber Attrappen intensive Kontaktreaktionen. Es wird die Frage diskutiert, ob das Erreichen einer bestimmten Eigröße eine Voraussetzung für das Entstehen des Kontaktverhaltens gewesen sein könnte.
• 6 Die Kurzkontakte junger T. tholloni werden aus ihrer Orientierungsreaktion abgeleitet und als Vorstufe des Kontaktverhaltens gedeutet.
• 7 7. Mehrere Tilapia-Arten wurden künstlich gekreuzt. Bei Verwendung von tholloni-Sperma wiesen die Bastarde eine erhöhte Sterblichkeit auf. Aus der Kreuzung T. tholloni ♀ ～ T. nilotica ♂ (Substratbrüter ～ weiblicher Maulbrüter) gingen nur ♀♀ hervor. Die Kreuzung T. heudeloti macrocephala ～ T. nilotica (männlicher ～ weiblicher Maulbrüter) erbrachte fertile F₁- und F₂-Generationen sowie alle vier möglichen Rückkreuzungen. Bei der Vererbung des Kontaktverhaltens (gemessen an der Dauer der Kontakte) scheinen relativ wenig Erbfaktoren mitzuwirken, T. heudeloti m. erwies sich gegenüber nilotica als praevalent. Ein Teil der Bastarde aus der Kreuzung T. tholloni ♀ ～ T. nilotica ♂ (F₁) (Substratbrüter ～ weiblicher Maulbrüter) lag auf der Merkmalsskala zwischen den Ausgangsarten, der Rest verteilte sich sowohl auf den Bereich von tholloni als auch auf den Bereich von nilotica.

     

Ionic dependence of the extracellular ATP-induced permeabilization of transformed mouse fibroblasts: role of plasma membrane activities that regulate cell volume

Extracellular ATP rendered the plasma membrane of transformed mouse fibroblasts permeable to normally impermeant molecules. This permeability change was prevented by increasing the ionic strength of the isotonic medium with NaCl. Conversely, the cells exhibited increased sensitivity to ATP when the NaCl concentration was decreased below isotonicity, when the KCl concentration was increased above 5 mM while maintaining isotonicity, and when the pH of the medium was raised above 7.0. These conditions as well as the addition of ATP itself caused cell swelling. However, the effect of ATP was independent of cell volume and dependent upon the ionic strength and not the osmolarity of the medium since 1) addition of sucrose to isotonic medium did not prevent permeabilization although media made hypertonic with either sucrose or NaCl caused a decrease in cell volume; and 2) addition of sucrose or NaCl to hypotonic media caused a decrease in cell volume, but only NaCl addition decreased the response to ATP. Conditions that have been shown to inhibit plasma membrane proteins that play a reciprocal role in cell volume regulation had reciprocal effects on the permeabilization process, even though the effect of ATP was independent of cell volume. For example, inhibition of the Na+,K+-ATPase by ouabain increased sensitivity of cells to ATP while conditions which inhibit Na+,K+,Cl- -cotransporter activity, such as treatment of the cells with the diuretics furosemide or bumetanide or replacement of sodium chloride in the medium with sodium nitrate or thiocyanate, inhibited permeabilization. The furosemide concentration that inhibited permeabilization was greater than the concentration that inhibited Na+,K+,Cl- -cotransporter-mediated 86Rb+ (K+) uptake, suggesting that the effect of furosemide on the permeabilization process may not be specific for the Na+,K+,Cl- -cotransporter.     

The genetic basis of adaptation to selection for longevity inDrosophila melanogaster

Summary Analysis of electrophoretic loci shows that at least four differences exist in isozymes of long- and short-lived populations ofD. melanogaster, descended by selection from a common ancestral stock. Adults of longlived populations differ in gene dosage of phosphoglucomutase (PGM), NAD malate dehydrogenase (MHD), NADP malic enzyme (ME) and by additional mobility variants of glucose-6-phosphate dehydrogenase (G6PD). Larvae, however, differ only by variants of G6PD. The differences in these enzymes, considered together with the greater flight endurance that long-lived populations have shown elsewhere, suggest that increased glycogen synthesis plays a significant role in the improved life span of selected populations. Adaptation to selection for increased life span may, therefore, derive from an improved ability to use dietary sucrose in the media provided. The distribution of electrophoretic loci agrees with the results of a study indicating the position of genetic elements contributing to life span.     

Using functional groups to investigate community response to environmental changes: two grassland case studies

Functional groups (FG) are an useful generalization to investigate environmental change effects on biotic communities. Assigning species to FGs is a contextual task and carries an arbitrary element, regardless of whether the grouping is obtained a priori or by sophisticated numerical methods. Using two grassland community case studies, we show that even simple FG allocation based on growth form, architecture and longevity (plants and mosses), or foraging characteristics (above-ground invertebrates) can be useful to increase our understanding of community processes. For example, the sensitivity of organisms to climate change increases with trophic rank and is higher in disturbed than in undisturbed communities. Complexity of interaction webs (in terms of web connectance), however, is larger in undisturbed than in disturbed communities. A significant and important relationship is likely to exist between anthropogenic disturbances, community complexity and the ecosystem effects of climate change. Trophic interactions may be disrupted much easier by climate changes in disturbed than in undisturbed communities where complexity may be buffering these effects.     

Developmental changes in responsiveness to vitamin D metabolites

We have demonstrated that epiphyseal chondroblasts contain specific receptors for 24R,25-dihydroxy vitamin D3(24,25(OH)2D3) while diaphyseal osteoblasts contain specific receptors for 1 alpha 25-dihydroxy vitamin D3(1,25(OH)2D3). Both metabolites induce DNA synthesis and creatine kinase (CKBB) activity. We have also found that the responsiveness of rat kidney to these metabolites changes during development. In embryonic and early postnatal stages, the kidney responds to 24,25(OH)2D3, later to both 24,25(OH)2D3 and 1,25(OH)2D3, and the mature kidney only to 1,25(OH)2D3. These responses correlate with changes in the specific receptors present in the kidney. Furthermore, we have compared developmental changes in skeletal (epiphysis, diaphysis and mandibular condyle) and non-skeletal (kidney, cerebellum, cerebrum, liver and pituitary) tissue in both rat (a postnatal developer) and rabbit (a perinatal developer). Epiphyseal or diaphyseal chondroblasts at any stage of development were predominantly responsive to 24,25(OH)2D3, whereas osteoblasts were responsive to 1,25(OH)2D3. In contrast, condylar chondroblasts, kidney, cerebellum and pituitary responded to 24,25(OH)2D3 during early development and subsequently developed responsiveness to 1,25(OH)2D3. Using primary cell cultures from kidneys at different stages of maturation, we showed the same developmental pattern as in vivo. Chronic treatment of the cells with 24,25(OH)2D3, but not 1,25(OH)2D3, caused precocious development of responsiveness to 1,25(OH)2D3 in culture. We suggest that 24,25(OH)2D3 acts as a maturation factor, during early development in kidney, and probably in other tissues, possibly by induction of receptor to 1,25(OH)2D3, accompanied by down-regulation of its own receptor.     

Variations among cell lines in the synthesis of sphingolipids in de novo and recycling pathways

There are several pathways for the incorporation of sugars into glycosphingolipids (GSL). Sugars can be added to ceramide that contains sphinganine (dihydrosphingosine) synthesized de novo (pathway 1), to ceramide synthesized from sphingoid bases produced by hydrolysis of sphingolipids (pathway 2), and into GSL recycling from the endosomal pathway through the Golgi (pathway 3). We reported previously the surprising observation that SW13 cells, a human adrenal carcinoma cell line, synthesize most of their GSL in pathway 2. We now present data on the synthesis of GSL in four additional cell lines. Approximately 90% of sugar incorporation took place in pathway 2, and 10% or less in pathway 1, in human foreskin fibroblasts and NB41A3 neuroblastoma cells. In contrast, approximately 50-90% of sugar incorporation took place in pathway 1 in C2C12 myoblasts. The C2C12 cells divide more rapidly and synthesize 10-14 times as much GSL as the other three cell lines. In C6 glioma cells, approximately 30% of sugar incorporation occurred in pathway 1 and 60% in pathway 2. There was no relation between the utilization of pathways for GSL and sphingomyelin synthesis in foreskin fibroblasts and C2C12 cells. In both cells pathways 1 and 2 each accounted for 50% of incorporation of choline into sphingomyelin. In five of the six cell lines that we have studied, most GSL synthesis takes place in pathway 2. We suggest that when the need for synthesis is relatively low, as in slowly dividing cells, GSL are synthesized predominantly from sphingoid bases salvaged from the hydrolytic pathway. When cells are dividing more rapidly, the need for increased synthesis is met by upregulating the de novo pathway.      

Maternal-perinatal interrelationships of vitamins D metabolism in rats

In pregnant rats it has been possible to show that the distribution of cholecalciferol metabolites in their fetuses reflects the distribution of these metabolites in the blood. In these experiments, pregnant rats were maintained on a vitamin D deficient diet but were supplemented with radiolabelled cholecalciferol. The metabolites found were 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol and, to a lesser extent, cholecalciferol. 1,25-Dihydroxycholecalciferol was not detected in fetal tissues, despite that ability of fetal kidney homogenates to hydroxylate 25-hydroxycholecalciferol in C-1.Kidney homogenates of newborn pups were found to possess marked activity of 25-hydroxycholecalciferol-24-hydroxylase, which was retained even in hypocalcemic pups born to pregnant rats that were fed a low-calcium diet.Injection of radiolabeled cholecalciferol to newborn pups resulted in the formation of 5/25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol. 1,25-Dihydroxycholecalciferol was not detected.Tissues thought of as target organs for vitamin D (in pregnant rats), namely, intestine, kidney and bone, were found to contain none or very little 1,25-dihydroxycholecalciferol.Mammary glands obtained from lactating rats were found to contain mainly the unchanged vitamin.     

Disruption of miR-29 Leads to Aberrant Differentiation of Smooth Muscle Cells Selectively Associated with Distal Lung Vasculature

Differentiation of lung vascular smooth muscle cells (vSMCs) is tightly regulated during development or in response to challenges in a vessel specific manner. Aberrant vSMCs specifically associated with distal pulmonary arteries have been implicated in the pathogenesis of respiratory diseases, such as pulmonary arterial hypertension (PAH), a progressive and fatal disease, with no effective treatment. Therefore, it is highly relevant to understand the underlying mechanisms of lung vSMC differentiation. miRNAs are known to play critical roles in vSMC maturation and function of systemic vessels; however, little is known regarding the role of miRNAs in lung vSMCs. Here, we report that miR-29 family members are the most abundant miRNAs in adult mouse lungs. Moreover, high levels of miR-29 expression are selectively associated with vSMCs of distal vessels in both mouse and human lungs. Furthermore, we have shown that disruption of miR-29 in vivo leads to immature/synthetic vSMC phenotype specifically associated with distal lung vasculature, at least partially due to the derepression of KLF4, components of the PDGF pathway and ECM-related genes associated with synthetic phenotype. Moreover, we found that expression of FBXO32 in vSMCs is significantly upregulated in the distal vasculature of miR-29 null lungs. This indicates a potential important role of miR-29 in smooth muscle cell function by regulating FBXO32 and SMC protein degradation. These results are strongly supported by findings of a cell autonomous role of endogenous miR-29 in promoting SMC differentiation in vitro. Together, our findings suggested a vessel specific role of miR-29 in vSMC differentiation and function by targeting several key negative regulators.