Feeding biology of two brachionid rotifers: Brachionus quadridentatus and Brachionus plicatilis

Brachionus quadridentatus and Brachionus plicatilis were examined in laboratory cultures to investigate their (1) food requirements and (2) ability to select particles on the basis of size. Growth experiments showed that the Chlorophyceans Nannochloris sp. and Chlorella vulgaris possess good nutritional value for these rotifers. However, B. quadridentatus declined in cultures with Microcystis firma, detritus of Enteromorpha sp. or Pseudomonas sp. (bacteria) as a sole source of food, thus indicating that these foods were inadequate. Utilization of latex microspheres by these two species indicate that they respond to particle size in different ways: B. quadridentatus had a higher selectivity index for 3 and 5 µm beads, while B. plicatilis had a higher selectivity index for 2 µm beads.     

MUTATIONAL MELTDOWNS IN SEXUAL POPULATIONS

Although it is widely acknowledged that the gradual accumulation of mildly deleterious mutations is an important source of extinction for asexual populations, it is generally assumed that this process is of little relevance to sexual species. Here we present results, based on computer simulations and supported by analytical approximations, that indicate that mutation accumulation in small, random-mating monoecious populations can lead to mean extinction times less than a few hundred to a few thousand generations. Unlike the situation in obligate asexuals in which the mean time to extinction (t?_e) increases more slowly than linearly with the population carrying capacity (K), t?_e increases approximately exponentially with K in outcrossing sexual populations. The mean time to extinction for obligately selfing populations is shown to be equivalent to that for asexual populations of the same size, but with half the mutation rate and twice the mutational effect; this suggests that obligate selfing, like obligate asexuality, is inviable as a long-term reproductive strategy. Under all mating systems, the mean time to extinction increases relatively slowly with the logarithm of fecundity, and mutations with intermediate effects (similar to those observed empirically) cause the greatest risk of extinction. Because our analyses ignore sources of demographic and environmental stochasticity, which have synergistic effects that exacerbate the accumulation of deleterious mutations, our results should yield liberal upper bounds to the mean time to extinction caused by mutational degradation. Thus, deleterious mutation accumulation cannot be ruled out generally as a significant source of extinction vulnerability in small sexual populations or as a selective force influencing mating-system evolution.     

BBReader: A computer program for the combined use of the BioMagResBank and PDB databases

A computer program (BBReader) was developed which performs an inverse search in theBioMagResBank database. Given (cross) peak positions of a protein, the program searchesfor atoms with matching chemical shifts and suggests possible assignments for user-specifiedhomo- and heteronuclear one- to three-dimensional COSY- and NOESY-type experiments.It can handle 1H, 13C and 15N spectra. Distance information from PDB files can be utilizedfor filtering possible NOESY cross peak assignments.     

Cholinergic Control of Nerve Growth Factor in Adult Rats: Evidence from Cortical Cholinergic Deafferentation and Chronic Drug Treatment

Abstract: It is well documented that nerve growth factor (NGF) plays an important role in maintaining functions of cholinergic basal forebrain neurons. In the present study, we tested the hypothesis that cholinergic activity controls NGF levels in cholinoceptive neurons of the cerebral cortex and hippocampus. To address that question, we used both cholinergic deafferentation of cerebral cortex and hippocampus by cholinergic immunolesion with 192IgG-saporin and chronic pharmacological treatment of sham-treated and immunolesioned rats with the cholinergic agonist pilocarpine and the cholinergic antagonist scopolamine. We observed an increase in NGF protein levels in the cortex and hippocampus after cholinergic immunolesions and also after muscarinic receptor blockade by chronic intracerebroventricular scopolamine infusion in sham-treated rats after 2 weeks. There was no further increase in the accumulation of NGF after scopolamine treatment of immunolesioned rats. Chronic infusion of pilocarpine had no effect on cortical and hippocampal NGF protein levels in sham-treated rats. In rats with cholinergic immunolesions, however, pilocarpine did prevent the lesion-induced accumulation of NGF. There was no effect of cholinergic lesion and drug treatment on cortical or hippocampal NGF mRNA levels, consistent with the importance of NGF retrograde transport as opposed to its de novo synthesis. This study provides strong evidence for the hypothesis that there is cholinergic control of cortical and hippocampal NGF protein but not mRNA levels in adult rats.     

Larval Planktotrophy—A Primitive Trait in the Bilateria?

The concept of Gösta Jägersten of a primary biphasic metazoan life-cycle, consisting of a planktotrophic larva and a benthic adult, forms the basis for several theories on metazoan phylogeny. In this paper the assumed planktotrophic life-style of the larva is critically analyzed and reconsidered. It is shown, in particular for the Mollusca, that a biphasic life-cycle with a lecithotrophic larva is probably the plesiomorphic condition. Character distribution and structural data suggest a parallel evolution of the downstream collecting system used in planktotrophic larvae or filter-feeding adults of gastropods, bivalves and other spiralian or aschelminth taxa. In the basic metazoans (Parazoa, Placozoa, coelenterates) direct or lecithotrophic development dominates by far. For the acoelomate (Platyhelminthes, Gnathostomulida) and pseudocoelomate taxa direct development is probably the plesiomorphic condition. The structural similarities of the upstream collecting system in tentaculate and deuterostome phyla may also be explained by parallel events of heterochrony out of an ancestor with adult filter-feeding. The main conclusion of this survey is that larval planktotrophy is likely to be secondary and not a plesiomorphic condition among the Bilateria. Accordingly, theories which are based on the assumed plesiomorphy of larval planktotrophy of the Bilateria, need careful reevaluation.     

One of three nuclear localization signals of maize Activator (Ac) transposase overlaps the DNA-binding domain

The nuclear localization sequences (NLSs) of the Ac transposase (TPase) protein have been characterized by indirect immunofluorescence detection of TPase deletion derivatives and TPase/β-glucuronidase (GUS) fusion proteins in transiently transfected Petunia cells. The TPase contains three NLSs near its amino-terminal end, NLS(44–62), NLS(159–178) and NLS(174–206), each of which is sufficient to redirect GUS to the nucleus. Deletion of the N-terminal 102 TPase residues including NLS(44–62) results in strongly reduced nuclear import of the truncated TPase. NLS(44–62) and NLS(159–178) are bipartite NLSs, whereas the structure of NLS(174–206) does not allow a classification into one of the three major NLS categories. NLS(174–206) overlaps with the basic DNA-binding domain of TPase. A substitution of two amino acids in this segment (HiS₁₉₁→Arg and Arg₁₉₃→His) results in a total loss of DNA-binding activity, but retains reduced NLS activity. Accordingly, the two functions can be separated. In addition, we show that a NLS-deficient 71 kDa TPase derivative is co-imported into the nucleus in the presence of wildtype TPase.     

Histidine decarboxylase: Isolation and molecular characteristics

High levels of histidine decarboxylase activity were measured in rat basophilic leukemia cells grown in ascitic form in 4 week old WKY/N rats. The potent inhibition of this enzyme by brocresine and -methylhistidine but not by -methyl DOPA identified it as a specific histidine decarboxylase. Gel filtration and polyacrylamide gel electrophoresis revealed a molecular weight of 125,000 for the native enzyme, similar to that of fetal rat liver histidine decarboxylase. Using rat basophilic leukemia cells as starting material, histidine decarboxylase was purified extensively in a seven step procedure. Electrophoresis under denaturing conditions revealed that histidine decarboxylase is a dimeric protein consisting of two identical subunits with a molecular weight of 62,000. The results indicate that rat basophilic leukemia cells provide a new and rich source for the purification of histidine decarboxylase.     

Fine structure of degenerating abdominal motor neurons after eclosion in the sphingid moth,Manduca sexta

Summary Ultrastructural aspects of the natural degeneration of a group of six motor neurons in the fourth abdominal ganglion of Manduca sexta are described. These motor neurons innervate intersegmental muscles that degenerate and disappear immediately after adult eclosion. The first detectable changes in the cell bodies appear 12 h after eclosion and include disruption of the endoplasmic reticulum and an increase in the size and number of lamellar bodies. At 32 h the nuclear membranes rupture, and the membranous and granular cytoorganelles segregate in different parts of the cell. At that stage the surrounding glial cells participate in the digestion of material from the degenerating neurons. From 72 h onward the remaining neuronal structures become disrupted, and are finally transformed into a single, large lamellar body (residual body) within the glial profile. The degeneration pattern differs significantly from that of embryonic vertebrate neurons.     

Cuticle ultrastructure of Hesionid polychaetes (Annelida)

Summary The structure of the cuticle in the four species of the family Hesionidae(Microphthalmus cf.listensis, M. cf.similis, Hesionides arenaria, juv.Podarke spec.) investigated basically corresponds to that found in all annelids. It consists of an outer, electron dense layer, epicuticle, basal cuticle with a fibrous layer, and numerous microvilli which penetrate the layers and are covered by a more or less dense glycocalyx. However, a rough collagen grid is not developed, the fibers are much thinner and are arranged in a more irregular manner. This corresponds to structures found in archiannelids and polychaete larvae. We consider them here to be reductions of the typical polychaete cuticle and postulate a correlation to the small body size of the species investigated. The quantitative differences in cuticle dimensions in the various body regions and structures can also be explained on a purely functional basis, especially apparent in the comparison of prostomium and body trunk. The pharynx cuticle shows significant structural differences due to the development of an additional peripherical lamellar layer-known to this extent only in gastrotrichs—as well as differently shaped and unusually long microvilli. This character is discussed as a possible synapomorphy for the family Hesionidae.

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Zusammenfassung Der Aufbau der Kutikula der 4 untersuchten Species aus der Familie Hesionidae(Microphthalmus cf.listensis, M. cf.similis, Hesionides arenaria, juv.Podarke spec.) entspricht grundsätzlich den Verhältnissen bei allen Anneliden: äußere elektronendichte Schicht, Epikutikula, basale Kutikula mit Faserschicht und zahlreiche Mikrovilli, die diese Schichten durchbrechen und von einem mehr oder weniger dichten Glykokalyx bedeckt sind. Ein derbes Kollagengitter ist jedoch nicht ausgebildet; die Fibrillen der Faserschicht sind wesentlich feiner und unregelmäßiger angeordnet. Dies entspricht Strukturen, wie sie bei Archianneliden und bei Polychaetenlarven gefunden werden. Wir deuten sie hier als Reduktionen der typischen Poly chaetenkutikula und vermuten eine Beziehung zur geringen Körpergröße der untersuchten Arten. Rein funktionell lassen sich auch die quantitativen Unterschiede in den verschiedenen Bereichen der Körperoberfläche deuten, die besonders im Vergleich von Prostomium und Rumpf zum Ausdruck kommen. Die Pharynxkutikula zeigt starke strukturelle Abweichungen durch die Ausbildung einer zusätzlichen peripheren Lamellenschicht (in diesem Ausmaß nur von den Gastrotrichen bekannt) und abweichend geformter, besonders langer Mikrovilli. Dieses Merkmal wird als mögliche Synapomorphie für die Familie Hesionidae diskutiert.