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Like many other social insect societies, honeybees collectively share the resources they gather by feeding each other. These feeding contacts, known as trophallaxis, are regarded as the fundamental basis for social behavior in honeybees and other social insects for assuring the survival of the individual and the welfare of the group. In honeybees, where most of the trophallactic contacts are formed in the total darkness of the hive, the antennae play a decisive role in initiation and maintenance of the feeding contact, because they are sensitive to gustatory stimuli. The sequences of behaviors performed by the receiver bees at the beginning of a feeding contact includes the contact of one antenna with the mouthparts of a donor bee where the regurgitated food is located. The antennal motor action is characterized by behavioral asymmetry, which is novel among communicative motor actions in invertebrates. This preference of right over left antenna is without exception even after removal of the antennal flagellum. This case of laterality in basic social interaction might have its reason in the gustatory asymmetry in the antennae, because the right antenna turns out to be significantly more sensitive to stimulation with sugar water of various concentrations than the left one. Trophallactic contacts which guarantee a constant access to food for every individual in the hive are vitally important to the honeybee society, because honeybees are heterothermic insects which actively regulate their thoracic temperature. Even though the individual can regulate its body temperature, its heating performance is strictly limited by the amount of sugar ingested. The reason for this is that honeybees use mostly the glucose in their hemolymph as the energy substrate for muscular activity, and the heat producing flight muscles are among the metabolically most active tissues known. The fuel for their activity is honey; processed nectar with a sugar content of ~80% stored in the honeycomb. The results show that the sugar content of the ingested food correlates positively with the thoracic temperature of the honeybees even if they are caged and show no actual heating-related behavior as in brood warming or heating in the centre of the winter cluster. Honeybees actively regulate their brood temperature by heating to keep the temperature between 33 °C to 36 °C if ambient temperatures are lower. Heating rapidly depletes the worker’s internal energy; therefore the heating performance is limited by the honey that is ingested before the heating process. This study focused on the behavior and the thoracic temperature of the participants in trophallactic food exchanges on the brood comb. The brood area is the centre of heating activity in the hive, and therefore the region of highest energy demand. The results show that the recipients in a trophallactic food exchange have a higher thoracic temperature during feeding contacts than donors, and after the feeding contact the former engage in brood heating more often. The donor bees have lower thoracic temperature and shuttle constantly between honey stores and the brood comb, where they transfer the stored honey to heating bees. In addition, the results show a heat-triggered mechanism that enables donor and recipient to accomplish trophallactic contacts without delay in the total darkness of the hive in the brood area as the most energy consuming part of the hive. Providing heat-emitting workers with small doses of high performance fuel contributes to an economic distribution of resources consistent with the physiological conditions of the bees and the ecological requirements of the hive, resulting in a highly economical resource management system which might be one of the factors favouring the evolution of perennial bee colonies in temperate regions. The conclusion of these findings suggests a resource management strategy that has evolved from submissive placation behavior as it is seen in honeybees, bumblebees and other hymenopterans. The heat-triggered feedback mechanism behind the resource management of the honeybee´s thermoregulatory behavior reveals a new aspect of the division of labor and a new aspect of communication, and sheds new light on sociality in honeybees.
Around 10.000 – 150.000 endogenous DNA damage-induced lesions occur in a human body per day and cell. Accumulation of unrepaired lesions can lead to aneuploidy and the loss of genomic integrity which in turn contributes to tumor formation. Therefore, an efficient DNA damage response has to be initiated, in the end leading to cell cycle inhibition and induction of repair. Since it is known that a recently characterized human multiprotein complex named LINC (or human dREAM) together with B-MYB is involved in the regulation of G2/M gene expression (Plk1, cyclin B1, cdc2 etc.), its function in the DNA damage response was analyzed in this study. In growing cells B-MYB is associated to the LIN core complex which consists of 5 different proteins named LIN-9, LIN-54, LIN-52, LIN-37 and RbAp48. After induction of DNA damage B-MYB leaves the complex and binding of E2F4 and p130 to LINC is induced. Importantly, the upstream pathway leading to LINC rearrangement is dependent on the activation of p53 and p21. Interestingly, p53 -/- cells solely have the potential to block in the G2 phase of the cell cycle, thereby making them vulnerable for errors during G2 arrest induction or maintenance. Here I demonstrate that LINC rearrangement is absent in p53 -/- cells and that B-MYB/LINC binding to target gene promoters is increased. This in turn leads to an increased G2/M gene expression after DNA damage induction and triggers premature cell cycle re-entry (checkpoint adaptation). Significantly, B-MYB expression is increased in p53 mutated primary breast cancer tumors and correlates with poor prognosis and reoccurrence probably due to its function in checkpoint adaptation. This study gives evidence that inhibition of B-MYB gene expression or B-MYB function in p53 mutant tumors could be a good choice for adjuvant therapy.
1 n order to review the contradictory statements on the ultrast ructure of the nuclear envelope, a study was undertaken combining section and negat ive stai ning electron microscopy on manually isolated oocyte nuclei and nuclear envelopes from six amphibian species including Anura as well as Urodela. The a ppeara nce of the negatively stained iso lated nuclear envelopes is described in deta il and the dependence on the preparation co nditions used is emphas ized . Pore complex structures such as pore perimeter, central granule, an nul ar components, interna l fibrils, and annu lus-attached fibrils could be identified by both techniques, negat ive staining and sect ions. Comparative studies show that no marked diffe rences ex ist in the structural data of the nuclear envelope among the investigated amphibians and the significance of the structural components is discussed. A model of the nuclea r pore complex based on the findings of the present investigation is prese nted.
Regulated progression through the cell cycle is essential for ordered cell proliferation. One of the best characterized tumor suppressors is the retinoblastoma protein pRB, which together with the E2F transcription factors regulates cell cycle progression. In the model organisms Drosophila melanogaster and Caenorhabditis elegans, RB/E2F containing multiprotein complexes have been described as transcriptional regulators of gene expression. This work first describes a homologous complex in human cells named LINC (for LIN complex). It consists of a stable core complex containing LIN-9, LIN-37, LIN-52, LIN-54 and RbAp48. This core complex interacts cell cycle-dependently with different pocket proteins and transcription factors. In quiescent cells, LINC associates with p130 and E2F4. In S-phase cells these interactions are lost and LINC binds to B-MYB and p107. The transient knock-down of LIN-54 in primary fibroblasts, as the depletion of LIN-9, leads to cell cycle defects. The cells are delayed before the entry into mitosis. This effect is due to the fact that the knock-down of LINC components leads to the downregulation of cell cycle genes responsible for the entry into and exit from mitosis as well as for checkpoints during mitosis. These LINC target genes are known E2F G2/M target genes, which are expressed later than the classical G1/S E2F target genes. The transcriptional regulation by LINC is a direct effect as LINC binds to the promoters of its target genes throughout the cell cycle. LINC contains three DNA-binding proteins. E2F4 and B-MYB, which cell cycle-dependently bind to LINC, are known DNA-binding transcription factors. Additionally, it is show here that the LINC core complex member LIN-54 also directly binds to the promoter of a LINC target gene. Although the exact molecular mechanism of LINC function needs to be analyzed further, data in this work provide a model for the delayed activation of G2/M target genes. B-MYB, a G1/S E2F target gene, binds to LINC upon its expression in S-phase. Then only LINC is a transcriptional activator that induces the expression of the G2/M genes. This provides an explanation for the delayed expression of these E2F G2/M target genes.
Eine der größten Herausforderungen in der Neurobiologie ist es, die neuronalen Prozesse zu verstehen, die Lernen und Gedächtnis zugrundeliegen. Welche biochemischen Pfade liegen z.B. der Koinzidenzdetektion von Reizen (klassische Konditionierung) oder einer Handlung und ihren Konsequenzen (operante Konditionierung) zugrunde? In welchen neuronalen Unterstrukturen werden diese Informationen gespeichert? Wie ähnlich sind die Stoffwechselwege, die diese beiden Arten des assoziativen Lernens vermitteln und auf welchem Niveau divergieren sie? Drosophila melanogaster ist wegen der Verfügbarkeit von Lern-Paradigmen und neurogenetischen Werkzeugen ein geeigneter Modell-Organismus, zum diese Fragen zu adressieren. Er ermöglicht eine umfangreiche Studie der Funktion des Gens S6KII, das in der Taufliege in klassischer und operanter Konditionierung unterschiedlich involviert ist (Bertolucci, 2002; Putz et al., 2004). Rettungsexperimenten zeigen, dass die olfaktorische Konditionierung in der Tully Maschine (ein klassisches, Pawlow’sches Konditionierungsparadigma) von dem Vorhandensein eines intakten S6KII Gens abhängt. Die Rettung war sowohl mit einer vollständigen, als auch einer partiellen Deletion erfolgreich und dies zeigt, dass der Verlust der phosphorylierenden Untereinheit der Kinase die Hauptursache des Funktionsdefektes war. Das GAL4/UAS System wurde benutzt, um die S6KII Expression zeitlich und räumlich zu steuern. Es wurde gezeigt, dass die Expression der Kinase während des adulten Stadiums für die Rettung hinreichend war. Dieser Befund schließt eine Entwicklungsstörung als Ursache für den mutanten Phänotyp aus. Außerdem zeigte die gezielte räumliche Rettung von S6KII die Notwendigkeit der Pilzkörper und schloss Strukturen wie das mediane Bündel, die Antennalloben und den Zentralkomplex aus. Dieses Muster ist dem vorher mit der rutabaga Mutation identifizierten sehr ähnlich (Zars et al., 2000). Experimente mit der Doppelmutante rut, ign58-1 deuten an, dass rutabaga und S6KII im gleichen Signalweg aktiv sind. Vorhergehende Studien hatten bereits gezeigt, dass die unterschiedlichen Ergebnisse bei operanter und klassischer Konditionierung auf verschiedenen Rollen für S6KII in den zwei Arten des Lernens hindeuten (Bertolucci, 2002; Putz, 2002). Diese Schlussfolgerung wurde durch den mutanten Phänotyp der transgenen Linien in der Positionskonditionierung und ihr wildtypisches Verhalten in der klassischen Konditionierung zusätzlich bekräftigt. Eine neue Art von Lern-Experiment, genannt „Idle Experiment“, wurde entworfen. Es basiert auf der Konditionierung der Laufaktivität, stellt eine operante Aufgabenstellung dar und überwindet einige der Limitationen des „Standard“ Heat-Box Experimentes. Die neue Art des Idle Experimentes erlaubt es, „gelernte Hilflosigkeit“ in Fliegen zu erforschen, dabei zeigte sich eine erstaunliche Ähnlichkeit zu den Vorgängen in komplizierteren Organismen wie Ratten, Mäusen oder Menschen. Gelernte Hilflosigkeit in der Taufliege wurde nur in den Weibchen beobachtet und wird von Antidepressiva beeinflusst.
Certain autoimmune sera contain antibodies against a nucleolar ribonucleoprotein particle associated with 7-2-RNA (R. Reddy et al. (1983) J. Bioi. Chem . 258, 1383; C. Hashimoto and J. A. Steitz (1983) J. Bioi. Chem. 258, 1379). In this study, we showed by immunofluorescence microscopy that antibodies reactive with 7-2-ribonucleoprotein immunolocalized in the granular regions of actinomycin D and 5,6-dichloro-I-j3-D-ribofuranosylbenzimidazole (DRB)-segregated nucleoli from Vero cells. By electron microscopic immunocytochemistry, antigen-antibody complexes were located in the granular component of transcriptionally active nucleoli from rat liver hepatocytes and HeLa cells. Anti-7- 2-RNP antibodies from two autoimmune sera immunoprecipitated a major protein of Mr 40,000 from e5S] methionine-Iabeled HeLa cell extract. The immunolocalization data suggest that 7-2-ribonucleoprotein may be involved in stages of ribosome biogenesis which take place in the granular component of the nucleolus, i.e., assembly, maturation, and/or transport of preribosomes
Repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. In the hnRNA population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. The structure and formation of duplex regions have been studied in the hnRNA of Xenopus laevis, Triturus cristatus, Amphiuma means and Necturus maculosus, a series of amphibians of increasing genome size (C-value). In T. cristatus, the duplex structures are mostly 600- 1200 bp in length, whereas in X. laevis they are shorter and in N. maculosus they tend to be longer. Although the proportion of RNA sequence capable of rapidly forming duplex structures is different in different organisms, this property bears no relationship to C-value. However the sequence complexity of complementary repeats, as estimated from the rate of duplex formation, does show an increasing trend with C-value. The complementary repeats found in oocyte hnRNA are transcribed from families of DNA sequence that are each represented in the genome by thousands of copies. The extent of cross-species hybridization is low, indicating that the repeat sequences transcribed in different amphibian genera are not the same. In situ hybridization experiments indicate that the repeat sequences are spread throughout the genome. The evolution and possible function of complementary repeats are considered.
The formation of daughter nuclei and the reformation of nucleolar structures was studied after microinjection of antibodies to RNA polymerase I into dividing cultured cells (PtK2). The fate of several nucleolar proteins representing the three main structural subcomponents of the nucleolus was examined by immunofluorescence and electron microscopy. The results show that the RNA polymerase I antibodies do not interfere with normal mitotic progression or the early steps of nucleologenesis, i.e. , the aggregation of nucleolar material into prenucleolar bodies. However,they inhibit the telophasic coalescence of the prenucleolar bodies into the chromosomal nucleolar organizer regions, thus preventing the formation of new nucleoli. These prenucleolar bodies show a fibrillar organization that also compositionally resembles the dense fibrillar component of interphase nucleoli . We conclude that during normal nucleologenesis the dense fibrillar component forms from preformed entities around nucleolar organizer regions, and that this association seems to be dependent on the presence of an active form of RNA polymerase I.
The ultrastructure of th e growin g and ma turing primary nucleus of Acetabularia medite rranea and Acetabularia major has been studied with the use of various fi xation procedures. Particular interest has been focused on the deta ils of the nuclear periphery and the perinuclear region. It is demonstrated that early in nuclear grow th a characteristic perinucl ear structura l complex is formed which is, among the eukaryotic cells, unique to Acetabularia and re lated genera. This perinuclear system consists essentially of a) the nuclear envelope with a very hi gh pore frequency and various pore complex assoc iat ion s w ith granular and/or threadlike structures some of which are continuous with the nucleolus; b) an approx imate ly 100 nm thick intermediate zone densely filled with a filam entOus material and occasional sma ll membraneous structures from which the typical cytOplasmic and nuclear organe lles and particles are excl ud ed ; c) an adjacent Iacunar labyrinthum which is interrupted by many plasmatic junction channels between the intermed iate zone and the free cytOplasm; d) numerous dense perinuclear bodies in the juxtanuclear cytOplasm which a re especia lly frequent at the junction channels and reveal a composition of aggregated fibrillar and granul ar structures; e) very dense exclusively fibrill ar agg regates which occur either in assoc iation with t he perinuclear region of the lacunar labyrinthum or, somewhat further out, in the cytOplasmic strands between the bra nches of the lacun ar labyrinthum in the form of slender, characteristic rods or "sausages".
The number of ribosomal RNA molecules which are transferred through an average nuclear pore complex per minute into the cytoplasm (nuclear pore flow rate, NPFR) during oocyte growth of Xenopus laevis is estimated. The NPFR calculations are based on determinations of the increase of cytoplasmic rRNA content during defined time intervals and of the total number of pore complexes in the respective oogenesis stages. In the mid-la mpbrush stage (500:"700 I'm oocyte diameter) the NPFR is maximal with 2.62 rRNA molecules/ pore/ minute. Then it decreases to zero at the end of oogenesis. The nucleocytoplasmic RNA f10w rates determined are compared with corresponding values of other cell types. The molecular weight of the rRNA precursor transcribed in the extrachromosomal nucleoli of Xenopus lampbrush stage oocytes is determined by acrylamide gel electrophoresis to be 2.5 x 10· daltons. From the temporal increase of cytoplasmic rRNA (3.8 I'g per oocyte in 38 days) and the known number of simultaneously growing precursor molecules in the nucleus the chain growth rate of the 40 S precursor RNA is estimated to be 34 nucleotides per second.